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Chapter 11
Climate Change, Ozone, and Ultraviolet Radiation
Contents
11.5.1.2. UV effects on terrestrial ecosystems . . . . . . . . 751
11.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717
11.5.1.2.1. Dwarf shrubs, mosses, and lichens 751
11.5.1.2.2. Decomposition . . . . . . . . . . . . . . . 751
11.2. Climate change. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
11.5.1.2.3. Animals. . . . . . . . . . . . . . . . . . . . . 752
11.2.1. Dynamic interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 718
11.5.2. Aquatic ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752
11.2.1.1. Energy balance . . . . . . . . . . . . . . . . . . . . . . . . 718
11.5.2.1. Climate change and marine ecosystems. . . . . . 752
11.2.1.2. Trace gas balance . . . . . . . . . . . . . . . . . . . . . . 719
11.5.2.1.1. Marine fish . . . . . . . . . . . . . . . . . . 752
11.2.1.3. Hydrological cycle . . . . . . . . . . . . . . . . . . . . . 719
11.5.2.1.2. Larger animals . . . . . . . . . . . . . . . 752
11.2.2. Climate change: Methods of assessment and recent trends 720
11.5.2.2. Photochemical effects of UV
11.2.2.1. Temperature records . . . . . . . . . . . . . . . . . . . . 720
Dissolved organic matter. . . . . . . . . . . . . . . . . 752
11.2.2.2. Radiatively important trace substances . . . . . . 723
11.5.2.3. UV and marine ecosystem . . . . . . . . . . . . . . . . 753
11.2.2.3. Water vapor . . . . . . . . . . . . . . . . . . . . . . . . . . 723
11.5.2.3.1. Primary producers . . . . . . . . . . . . 754
11.2.2.4. Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . 723
11.5.2.3.2. Bacteria . . . . . . . . . . . . . . . . . . . . 755
11.2.2.5. Hydroclimatology . . . . . . . . . . . . . . . . . . . . . 725
11.5.2.3.3. Zooplankton. . . . . . . . . . . . . . . . . 755
11.2.2.6. Sea ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
11.5.2.3.4. Invertebrates . . . . . . . . . . . . . . . . . 755
11.2.2.7. Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . 725
11.5.2.3.5. Fish populations . . . . . . . . . . . . . . 755
11.2.2.8. Soils and permafrost . . . . . . . . . . . . . . . . . . . . 726
11.5.2.3.6. Larger animals . . . . . . . . . . . . . . . 755
11.2.2.9. Glaciers and ice sheets. . . . . . . . . . . . . . . . . . . 726
11.5.2.4. Climate change and Arctic freshwater. . . . . . . 755
11.2.2.10. Ice and sediment cores . . . . . . . . . . . . . . . . . 726
11.5.2.4.1. Climate change and Arctic lakes
11.2.2.10.1. Ice cores . . . . . . . . . . . . . . . . . . . 726
and ponds . . . . . . . . . . . . . . . . . . . 755
11.2.2.10.2. Paleoecological records . . . . . . . . 727
11.5.2.4.2. Climate change and rivers and streams 756
11.2.2.11. Historical and archaeological evidence . . . . . 728
11.5.2.5. UV and Arctic freshwater . . . . . . . . . . . . . . . . 756
11.2.3. Ability to predict . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728
11.2.4. Components of the Arctic . . . . . . . . . . . . . . . . . . . . . . . 729
11.6. Effects of climate change and UV radiation on Arctic peoples 757
11.2.4.1. Oceanic regime . . . . . . . . . . . . . . . . . . . . . . . . 729
11.6.1. Pre-historical and historical effects of climate change . . 757
11.2.4.1.1. Ocean stratification and water
11.6.2. Settlement and resource use . . . . . . . . . . . . . . . . . . . . . . 757
circulation. . . . . . . . . . . . . . . . . . . 729
11.6.3. Economic activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
11.2.4.1.2. Sea ice . . . . . . . . . . . . . . . . . . . . . . 730
11.6.3.1. Commercial fisheries . . . . . . . . . . . . . . . . . . . . 758
Leads and polynyas . . . . . . . . 730
11.6.3.2. Reindeer herding. . . . . . . . . . . . . . . . . . . . . . . 758
Snow cover . . . . . . . . . . . . . . . 731
11.6.3.3. Transportation . . . . . . . . . . . . . . . . . . . . . . . . 758
Melt ponds . . . . . . . . . . . . . . . 731
11.6.3.4. Forestry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758
11.2.4.2. Terrestrial regime . . . . . . . . . . . . . . . . . . . . . . 731
11.6.3.5. Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
11.2.4.2.1. Soil . . . . . . . . . . . . . . . . . . . . . . . . 731
11.6.4. Effects of UV radiation on human health. . . . . . . . . . . . 759
11.2.4.2.2. Permafrost . . . . . . . . . . . . . . . . . . 731
11.7. International efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
11.2.4.2.3. Runoff . . . . . . . . . . . . . . . . . . . . . 732
11.7.1. Agreements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
11.2.4.2.4. Snow . . . . . . . . . . . . . . . . . . . . . . 732
11.7.2. Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
11.2.4.2.5. Terrestrial ecosystems Physical
11.7.3. Assessments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760
properties . . . . . . . . . . . . . . . . . . . 733
11.7.3.1. Climate change . . . . . . . . . . . . . . . . . . . . . . . . 760
11.2.4.2.6. Arctic glaciers and ice sheets . . . . . 733
11.7.3.2. Ozone and UV . . . . . . . . . . . . . . . . . . . . . . . . 760
11.2.4.3. Atmospheric regime . . . . . . . . . . . . . . . . . . . . 734
11.8. Conclusions and recommendations . . . . . . . . . . . . . . . . . . 761
11.2.4.3.1. Atmospheric structure and components 734
11.8.1. Climate change: Conclusions . . . . . . . . . . . . . . . . . . . . . 761
Temperature . . . . . . . . . . . . . . 734
11.8.2. Climate change: Recommendations . . . . . . . . . . . . . . . . 761
Surface winds . . . . . . . . . . . . . 734
11.8.3. Ozone: Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761
Clouds . . . . . . . . . . . . . . . . . . 735
11.8.4. Ozone: Recommendations . . . . . . . . . . . . . . . . . . . . . . . 761
11.2.4.3.2. Radiatively important trace substances 735
11.8.5. UV: Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761
Carbon dioxide . . . . . . . . . . . 736
11.8.6. UV: Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . 762
Methane (CH4) . . . . . . . . . . . 736
11.8.7. Climate change and UV effects on ecosystems: Conclusions 762
Carbon monoxide . . . . . . . . . 736
11.8.8. Climate change and UV effects on ecosystems:
Nitrous oxide (N2O) . . . . . . . 736
Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
Chloroflourocarbons (CFCs) . 737
11.8.9. Climate change and UV effects on humans: Conclusions 762
Water vapor . . . . . . . . . . . . . . 737
11.8.10. Climate change and UV effects on humans:
Aerosols . . . . . . . . . . . . . . . . . 737
Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
Tropospheric ozone . . . . . . . . 738
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
11.3. Arctic stratospheric ozone . . . . . . . . . . . . . . . . . . . . . . . . . . 739
11.3.1. Arctic stratospheric ozone . . . . . . . . . . . . . . . . . . . . . . . 739
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763
11.3.2. Chemistry of ozone depletion Polar vortex dynamics . 739
11.3.3. Measurements of stratospheric ozone . . . . . . . . . . . . . . 740
11.3.4. Results of measurements . . . . . . . . . . . . . . . . . . . . . . . . 740
11.3.5. Arctic ozone anomalies . . . . . . . . . . . . . . . . . . . . . . . . . 742
11.1. Introduction
11.3.5.1. Type 1 Arctic ozone anomaly . . . . . . . . . . . . . 742
11.3.5.2. Type 2 Arctic ozone anomaly . . . . . . . . . . . . . 744
Global climate change is a growing concern, especially in
11.4. UV radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744
Arctic regions where increases in temperature from anthro-
11.4.1. Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745
pogenic influences could be considerably higher than the
11.4.2. Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 746
global average. Climatic changes are not new to the Arctic
11.4.3. Biologically relevant UV. . . . . . . . . . . . . . . . . . . . . . . . . 746
11.4.3.1. Spectral considerations . . . . . . . . . . . . . . . . . . 746
or its peoples. Indigenous peoples of the far north have
11.4.3.2. Geometrical considerations . . . . . . . . . . . . . . . 746
adapted to the austere climate; different groups have found
11.4.4. UV on land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 747
their own unique ways to harvest food and provide clothing,
11.4.5. UV penetration in aquatic systems . . . . . . . . . . . . . . . . . 748
tools, and shelter. At times the climate has warmed or cooled
11.5. Effects of climate change and UV radiation on the biosphere 749
11.5.1. Terrestrial ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . 749
relatively suddenly and people have either adapted, moved,
11.5.1.1. Climate change effects on terrestrial ecosystems 749
or died off. The paleo-archaeological record, indigenous
11.5.1.1.1. Vegetation. . . . . . . . . . . . . . . . . . . 749
peoples' oral history, and historical documents provide evi-
Plant communities . . . . . . . . . 749
Nutrient availability . . . . . . . . 750
dence of climatic changes for thousands of years. Today,
Permafrost and vegetation . . . 750
people of the Arctic, whether they continue to live close to
Water stress . . . . . . . . . . . . . . 750
11.5.1.1.2. Invertebrates . . . . . . . . . . . . . . . . . 750
the land or live in urban centers, must again confront rapid
11.5.1.1.3. Vertebrates . . . . . . . . . . . . . . . . . . 750
changes in climate. Various records over the last 40 years
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AMAP Assessment Report
confirm that the rate of global warming has been greatest
dressed. Little effort has been expended to study the effects
over Eurasia and North America between 40°N and 70°N
of UV on the Arctic biosphere, including human health, al-
(IPCC 1996a). Arctic research substantiates these observa-
though the International Arctic Science Committee con-
tions through direct and indirect indicators of climate change.
cluded in 1995 that `There is a pressing need to quantify
Sea ice, snow cover, glaciers, tundra, permafrost, boreal for-
ozone-dependent UV-B effects on diverse Arctic ecosystems
ests, and peatlands are all responsive to subtle variations in
under their current conditions.'
sunlight, surface temperature, ocean heat transport, air and
This chapter provides an overview of current research
ocean chemistry, and aerosols in the atmosphere. Compared
and knowledge on climate change, ozone depletion, and
with the rest of the globe, the Arctic climate is very sensitive
UV-B radiation in the Arctic. After this brief introduction,
to change because of a complex series of interactions and
the second section gives an overview of climate change, in-
positive feedback processes among the region's oceanic and
cluding evidence and measurements of climate change as
atmospheric circulation patterns, temperature regime, hy-
well as what is known about the various components of the
drologic cycle, and sea ice formation (Barry et al. 1993a,
climate change system in the Arctic. Section three addresses
Kellogg 1983, Mysak 1995).
stratospheric ozone, and section four covers UV radiation in
Present models of the Arctic climate system suggest that
the Arctic. The general effects of climate change and UV ra-
positive feedbacks in high-latitude systems amplify anthro-
diation on aquatic and terrestrial ecosystems are examined
pogenically-induced atmospheric changes and that distur-
in section five, and section six examines their effects on Arc-
bances in the circumpolar Arctic climate may substantially
tic peoples and their communities. Section seven provides an
influence global climate (IPCC 1990a, 1992a, 1996a). The
overview of major international programs involving research
extreme sensitivity of the Arctic's climatic and ecological
and assessments. Recommendations for further international
systems implies that the Arctic will be profoundly affected
efforts are made in section eight.
by anthropogenic climate change (Quadfasel et al. 1991,
Walsh 1991). Both positive and negative feedbacks compli-
cate Arctic climate change, making it difficult to model or
11.2. Climate change
predict. A number of different positive feedbacks have been
11.2.1. Dynamic interactions
identified for the Arctic. For example, sea ice and snow re-
flect a much larger fraction of incident sunlight than water
The complexity of climate change in the Arctic can be ob-
and soil, so that a reduction of sea ice and snow causes a
served through the strong and dynamic changes in the en-
perturbation in the energy budget, amplifying warming in
ergy, trace gas and hydrological balances of the Arctic. Solar
the Arctic. This warming is transferred globally and, at the
radiation inside the Arctic Circle varies seasonally from con-
same time, feeds back regionally to further reduce snow and
tinuous sunlight to no sunlight. Depending on ambient con-
ice extent. Concurrently, as temperature rises the air is able
ditions, the Arctic can be either a source or a sink of particu-
to hold more moisture which increases the greenhouse ef-
lar trace gases. The water balance of the Arctic is highly dy-
fect, adding to the temperature increase. Of course, actual
namic in its exchange between ice, water, and water vapor.
processes of climate change are not so simple and data
Virtually all components and aspects of the Arctic climate
analyses reveal conflicting trends in climate and tempera-
system, from sea ice to surface temperature, are determined
ture. Other subtle systemic feedback mechanisms which
integrally by the energy, trace gas, and hydrological cycles.
could offset the primary feedbacks may be present. In sum-
The balance of these three systems will be discussed first to
mary, while strong positive feedback mechanisms have been
allow an overview before the individual components of the
identified and are expected to play major roles in climate
Arctic climate system are covered in more detail.
change in the future, the complex interactions of these and
other environmental feedbacks, both positive and negative,
11.2.1.1. Energy balance
are not fully understood.
Another major factor affecting climate is stratospheric
Alteration of the Earth's radiation balance is the most direct
ozone. Stratospheric ozone is an important indicator, as
way to affect climate. The Earth's surface temperature is a
well as an agent, of climate change. Stratospheric cooling,
result of the balance between the energy fluxes in a small
a direct result of what is generally referred to as global
layer near the surface. The amount of solar radiation ab-
warming, allows for increased ozone destruction in the Arc-
sorbed by the surface is determined by many factors. Apart
tic. As an absorber of solar radiation, ozone partly controls
from solar elevation angle and day length, the most impor-
the temperature structure of the atmosphere, influencing
tant factors are atmospheric scattering and absorption by
dynamical as well as thermal properties of the atmosphere.
clouds, haze, atmospheric chemistry, and surface albedo.
Ozone depletion is an increasing concern in the Arctic as
Net radiation (the balance between longwave and shortwave
anomalously low levels of ozone have been recorded in re-
fluxes) in the Arctic is strongly positive in the summer and
cent years. The Scientific Assessment of Ozone Depletion:
negative in the winter. The interactions and feedbacks be-
1994 concluded that `Chlorine- and bromine-catalyzed
tween cloud cover, albedo (percentage of incoming radiation
ozone loss has been confirmed in the Arctic Winter' (WMO
reflected), radiation, sea ice, and snow cover are important
1995). The destruction of ozone increases UV radiation at
modulators of the radiation balance and represent key un-
the earth's surface, making ozone critically important to the
certainties in evaluating the role of the Arctic in the global
well-being of the biosphere and human health.
climate system. The latent heat flux is near zero in the win-
The increase in UV has become more significant since
ter, when there is very little capacity for the air to hold mois-
evidence shows that changes in UV levels due to ozone de-
ture; in the summer it is usually negative, indicating evapo-
pletion can be large, particularly in spring-time. Elevated UV
ration. The sensible heat flux is a principal component of
levels adversely affect aquatic and terrestrial ecosystems, as
the surface energy balance in the winter over continents as
well as humans. A combination of high early-summer bio-
is the conductive flux over the oceans. The conductive flux
logical activity and changes in UV levels makes the Arctic an
depends on the ice thickness and snow cover and is the
area where ozone depletion may have notable effects in the
cause of the relatively warm temperatures observed over
near future. Many questions remain which need to be ad-
the frozen oceans.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
719
Sea ice cover
11.2.1.2. Trace gas balance
melts and
shrinks
The greenhouse effect, i.e. the warming of the troposphere
and the Earth's surface from the absorption of infrared radi-
Temperatures
warm
ation by certain gases, is one of the important forcing mech-
anisms of climate. Carbon dioxide (CO2), methane (CH4),
A change:
temperatures
nitrous oxide (N2O), tropospheric ozone (O3), and chloro-
warm
Temperatures
fluorocarbons (CFCs) are the most important ones, and their
warm
atmospheric abundances have all increased since the last cen-
tury. The calculated direct global mean change in the surface
radiative heat balance is +2.5 W/m2 due to the addition of
Ocean waters
Sea ice cover
the above gases (O3 not included), without taking any poten-
absorb more solar
radiation than
melts and
tial feedbacks into consideration (IPCC 1996a). This amount
highly reflective
shrinks
sea ice
is equal to one percent of the global mean solar radiative
forcing at the surface.
Greenhouse gases are emitted, stored, and absorbed by
ecosystems on the land and in the oceans as a result of nat-
Figure 11·1. An example of a positive feedback loop. Warming leads to a de-
ural processes. The concentrations of these gases can be
crease in sea ice cover which in turn leads to a decrease in albedo over the
altered as a result of industrial development. Long-lived
ocean, the result of which is further warming and further decreases in the
trace gases (>1 year) have global influences because they are
sea ice cover. In the reverse situation, if sea ice cover, and hence albedo, were
to increase, the feedback would lead to cooler air temperatures, thus promot-
redistributed by transport in the atmosphere. A shorter-lived
ing greater sea ice cover. In either case, the feedback loops are positive, i.e.
gas such as ozone has a more regional influence. Because of
the change is amplified by the system feeding-back onto itself. Negative feed-
greater atmospheric stability, the concentrations of many
backs help regulate a system causing changes to be moderated or diminished.
trace gases in the Arctic tend to be somewhat higher in the
Changes in sea ice extent have a major bearing on the en-
cold season.
ergy related processes between ocean and atmosphere. This
Perturbations to climate in the Arctic may increase the
dependence has been described as sea ice-albedo feedback,
emissions of CO2, CH4, and N2O, which will feed back into
i.e. the chain of events following an initial warming of the
the global forcing of climate. The emissions are influenced
near-surface temperatures, a reduction in sea ice, and a sub-
by a host of factors, such as soil temperature and moisture,
sequently enhanced energy transfer from atmosphere to ocean,
nutrient deposition/loss, snow cover, cloud cover, and sea ice
which leads to further reductions in sea ice. This dependence
extent. Acting slowly over decades, but no less important to
is shown in Figure 11·1. A similar process operates over
the trace gas balance, are changes in the species composition
snow-covered land.
of Arctic ecosystems that are likely to result from climate
Cloud cover, extent of sea ice, and snow cover can influ-
change. All of these processes are poorly or incompletely un-
ence the planetary albedo and large-scale albedo gradients,
derstood. Understanding the complex systems governing
with consequent impacts on atmospheric circulation. As sur-
trace gases is crucial to predicting future climate changes.
face fluxes of solar and long-wave radiation are strongly in-
fluenced by cloud cover, variations in cloudiness affect polar
11.2.1.3. Hydrological cycle
sea ice and snow cover. Along with a direct effect on the ra-
diation balance, clouds have an indirect bearing on the sta-
The hydrological cycle of the Arctic encompasses a variety
bility of the atmospheric boundary layer and thus on the
of components (Figure 11·2) including precipitation, sea ice,
sensible and latent heat fluxes.
river run-off, glaciers, icebergs, clouds, and humidity. Water
Sun
R
S
L cloud
T
T
P
P
L cloud
R
L ice
L air
R
R
FL
FL
Fc
I
Ice
I
Ice
Ocean
F: Turbulent heat flux in water ( FL - Latent heat flux due to evaporation and condensation, Fc - Convective flux) I: Absorbed radiation L: Thermal infrared radiation
fluxes P: Precipitation R: Albedo (Reflection) S: Solar infrared radiation fluxes T: Net advection of moist static energy.
Figure 11·2. The hydrologic balance in the Arctic is highly dynamic on the seasonal time scale with large and rapid ice melts in the spring. On land, this
ice and snow melting results in large rapid floods and surges in rivers. In the oceans, the ice melt results in large areas of the Arctic becoming available
for biological growth and activity. On longer time scales, climate change in the Arctic could release glacial waters increasing the present sea level globally.
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AMAP Assessment Report
transport and storage in the Arctic are fundamentally differ-
ent than in other parts of the world. Much of the water in
the Arctic is frozen most of the time. Seasonal freeze/thaw cy-
cles of sea ice, snow, and permafrost, and perennial freezing
of the polar ice cap, glaciers, and below-ground ice control
the exchange of water, trace gases, and water-borne materials.
Water vapor and temperature are closely related to the hy-
drological cycle in both the oceanic and terrestrial regions.
Leads and polynyas in sea ice release a large flux of water
vapor into the atmosphere. Similarly, warmer air tempera-
tures and open water in lakes and drainage systems and melt-
ing of permafrost allow water vapor to be released into the
atmosphere. This water vapor is then available for cloud for-
mation and potential precipitation release elsewhere.
The Arctic region's oceans include 25% of the world's
continental shelf areas. Of all of the world's coastal waters,
the near-shore Arctic Ocean is the region most affected by
the delivery of freshwater from the adjoining drainage system
(Aagaard and Carmack 1989). These discharges may in turn
exert important controls on the formation of Arctic sea ice
Period of record, years
and hence the albedo and radiation balance of the planet;
less than 5
changes in delivery of freshwater from a warming climate
5 to 10
20 to 30
would thus affect the global energy balance (Semtner 1987,
10 to 20
more than 30
Rowntree 1989, Allard et al. 1995, cf. Hakkinen 1990).
Figure 11·3. Locations of upper-air meteorological monitoring stations in
the Arctic (from Kahl et al. 1992). Meteorological station density for sur-
11.2.2. Climate change: Methods of assessment
face observations is greater for inland areas of the Arctic, while observa-
and recent trends
tions of any kind are sparse over the Arctic Ocean.
A variety of direct and indirect methods are available to assess
peratures is limited because of large areas that have never
climatic and environmental changes over a range of spatial
been monitored or have been monitored only sporadically in
and temporal scales. It is clear that examination of both direct
space and time (Figure 11·3). Few stations north of 70°N
and indirect indicators of climate change on short and long
are available either on land or on sea ice, and data from
time scales is necessary to understand the Arctic's climate his-
them must be augmented with drifting-buoy data (Colony
tory, to make policy decisions about anthropogenic effects on
and Thorndike 1984) and remotely-sensed information
climate, and to make valid predictions about the future.
(Maslanik et al. 1996). Multi-decadal trends have been de-
Sources of climate information are of varied quantity and
termined for available surface and upper-air temperatures.
quality and can be difficult to interpret. Recent trends of en-
Trend analyses of surface temperatures typically rely on
vironmental change frequently conflict with one another and
gridded surface temperature datasets representing an assimi-
existing data are often insufficient to provide a clear picture.
lation of raw station observations (Chapman and Walsh
Surface air temperature is the most obvious direct indicator
1993, IPCC 1990a, 1992a). Upper-air analyses are based on
of climate change, yet circum-Arctic temperature records are
rawinsonde or dropsonde temperature profiles (Kahl et al.
not long and are particularly sparse over the Arctic Ocean.
1993a, 1993b) and satellite monitoring platforms (Christy
Indirect indicators such as borehole temperatures, snow
1995). The determination of long-term trends is hampered
cover extent, glacier recession, precipitation, and vegetation
by non-climatic factors which can obscure real trends or
changes yield data that so far support direct indicators of
produce artificial ones. These factors include changes in in-
warming (IPCC 1996a). While meteorological measurements
strument response characteristics, balloon ascent rates, data
provide temperature and precipitation records on short time
reporting, and correction procedures (Gaffen 1994, Parker
scales, paleoecological studies and historical records provide
and Cox 1995, Skony et al. 1994).
evidence of past changes in climate. Early records of plant
Surface temperatures in the Arctic vary widely over land
and animal life contained in ice, fossils, and sediment cores
and sea. Analyses of surface observations indicate that warm-
reveal long-term changes in the environment, while ice cores
ing has occurred over the northern land masses during the
can provide evidence of mean or extreme temperatures and
past century (Jones 1994, Parker et al. 1995, IPCC 1996a).
atmospheric gas composition over 200 000 years or more
Inland Arctic areas of central Siberia and North America
(Alley et al. 1996). Glacier mass has been used to derive esti-
have warmed by 1.5°C per decade (Jones and Briffa 1992).
mates of warming since the end of the Last Ice Age.
This warming trend is particularly evident in winter and
Indigenous peoples and historical records provide informa-
spring (Chapman and Walsh 1993) (Figure 11·4). Cooling
tion about a variety of climate change indicators such as
trends of 1.5°C per decade have been observed over eastern
changes in animal populations, plant distribution, water lev-
North America and through the North Atlantic. Surface
els, sea ice thickness and extent, and temperature and precip-
temperature trends over Fennoscandia and the subarctic seas
itation, while archaeological research can help reveal local
are smaller and even negative in the southern Greenland re-
and regional climatic changes.
gion (Jones et al. 1986).
For upper air temperatures, systematic balloon measure-
ments (radiosondes) have been made since the 1950s for
11.2.2.1. Temperature records
approximately 50 locations in the Arctic region (Parker
Surface and atmospheric temperatures in the Arctic have
and Cox 1995, Kahl et al. 1992). Since 1979, satellites
changed in complex and variable ways over the past several
have been able to monitor nearly all of the polar region,
decades. Knowledge of long-term variations in Arctic tem-
both for the lower troposphere and lower stratosphere
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
721
Spring
Summer
Autumn
Winter
°C per decade
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
Figure 11·4. Seasonal and annual average surface temperature trends (°C
per decade) over the northern hemisphere.
(Christy 1995). Analyses of radiosonde measurements for
coastal and inland Arctic stations (Figure 11·3) from 1958-
1986 indicate regions of warming and cooling, but there is
no general circumpolar trend and trends at most stations are
not statistically significant (Kahl et al. 1993b, Michaels et al.
1995). Tropospheric temperature profiles over the Arctic
Ocean similarly fail to reveal widespread significant trends
since 1950, although surface cooling has been detected in
winter and autumn (Kahl et al. 1993a). Further analysis of
lower tropospheric temperatures over the Arctic Ocean has
revealed a strengthening of the thermal stability of the Arctic
inversion layer (Kahl et al. 1996), which exerts a strong in-
fluence on Arctic pollution as well as on fluxes of mass and
momentum between the atmosphere, ice, and ocean.
Satellite monitoring of lower tropospheric temperatures
since 1979 (Christy 1995) suggests an Arctic warming trend
Annual
of 0.05°C per decade, somewhat greater than that of the Earth
722
AMAP Assessment Report
Degrees (°C) from the long term mean
Global average
1.0
Trend = -0.038 °C per decade
0.0
-1.0
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
Degrees (°C) from the long term mean
Arctic
Trend = +0.052 °C per decade
3.0
0.0
-3.0
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
Figure 11·5. Lower tropospheric temperatures since 1979, from satellite monitoring (Christy 1995). High variability is characteristic of the Arctic region
due to its isolation from the moderating influences of warm, lower latitude, ocean currents.
as a whole (Figure 11·5). However, trend values over short
temperatures fell to lower levels than pre-eruption values
periods are very sensitive to natural fluctuations occurring
in both episodes.
at the beginning and end of the time series. In the Arctic,
The Arctic stratospheric cooling trend of -1.01°C per de-
temperature comparisons of the lower troposphere with
cade (Figures 11·6 and 11·7) is the largest decrease seen on
the surface indicate that the surface is warming more rap-
the globe. Loss of stratospheric ozone is related to the de-
idly. The lower stratospheric temperature record reveals
creasing temperature since ozone maintains the temperature
large fluctuations since 1979 (Christy 1995). The global
in the stratosphere by absorbing heat. The geographic pat-
record shows two episodes of remarkably sudden stratos-
tern of the stratospheric trends (Figure 11·7) is more uni-
pheric warming caused by infrared-absorbing aerosols
form than in the troposphere (Figure 11·8), suggesting that
from volcanic eruptions: the combination of Nyamuragria
the physical forcing mechanisms for tropospheric climate
and El Chichon in 1981 and 1982, and then Mount Pina-
change are more strongly dependent upon regionally varying
tubo in 1991 (Figure 11·6). Globally, post-eruption surface
surface processes.
Degrees (°C) from the long term mean
Global average
2.0
Trend = -0.410 °C per decade
0.0
-2.0
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
Degrees (°C) from the long term mean
Arctic
15.0
Trend = -1.010 °C per decade
0.0
-15.0
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
Figure 11·6. Lower stratospheric temperature record since 1979 (Christy 1995). Large variations in stratospheric temperatures are due to sudden
stratospheric warming and cooling (SSWC) events which occur in Nother winter (and are related to tropospheric planetary waves), and the impact of
volcanic aerosols. The north polar regions exhibit the most dramatic cooling trend of the planet, which is consistent with Arctic ozone depletion.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
723
Currently the Arctic tundra as a whole is a sink for CO2,
yet changes in vegetation could reverse the net CO2 flux and
-1.50
increase global warming. Already, results of studies of CO2
on two tundra ecosystems (Oechel et al. 1993, 1994, Mal-
mer and Wallen 1996) indicate they have switched from
-1.50
being sinks to being sources of atmospheric carbon due to
recent warming. It is estimated that between 10 and 25% of
-1.25
-1.25
global wetland emissions of CH4 are from north of 60º
(Matthews 1993). Whalen and Reeburgh (1992) showed
that CH4 emission in a very wet year could be four times
-1.00
-1.00
that in a dry year, suggesting that increased precipitation
and thawing permafrost could release a globally significant
-0.75
amount of CH4 into the atmosphere.
Recent studies show that air from lower latitudes, con-
taining high mixing ratios of N2O, can be transported north-
-0.50
-0.75
ward and entrained into the polar vortex while air masses
containing low mixing ratios of N2O can be stripped off of
-0.50
the polar vortex and transported to mid-latitudes (Kumer et
al. 1993, Manney et al. 1994b, 1995b, Ruth et al. 1994, Sut-
-0.25
ton et al. 1994, Waugh et al. 1994). The extent to which this
happens and the degree to which springtime mid-latitude
ozone depletions are linked to these polar processes is still a
Figure 11·7. Lower stratospheric (ca. 120-40 hPa) Arctic temperature
matter of debate and needs further investigation. Vertical
trends (°C per decade, January 1979 to February 1996), as monitored by
profile measurements (ozonesondes) over the Canadian
MSUs on polar orbiting satellites. The entire Arctic stratosphere has expe-
Arctic show significant declines in ozone at all altitudes and
rienced a cooling trend which is maximised over Siberia.
at all locations since the mid-1980s (Tarasick et al. 1995,
Logan 1994, Oltmans 1993) (see Figure 11·14, section
0.50
11.2.4.3.2). Of relevance to radiative forcing, ozone concen-
0.25
0
trations in the upper troposphere affect the energy budget,
0
0.25
and a recent declining trend in tropospheric ozone may
counteract warming caused by other substances.
-0.25
11.2.2.3. Water vapor
0.25
Water vapor in the atmosphere is an integral part of the cli-
0
mate system. In the Arctic, water vapor is an important part
of the energy and hydrological cycles, particularly near leads
0
0.50
and polynyas. Water vapor is also a radiatively active gas;
-0.25
0
and changes in its concentration affect the Arctic climate.
Globally, there are no available observations with which to
0.25
judge long-term changes in water vapor (IPCC 1994). How-
0.25
ever, increases in methane are expected to be accompanied
0
by increases in stratospheric water vapor.
-0.25
0.25
11.2.2.4. Precipitation
-0.50
0
Precipitation is a valuable and sensitive indicator of climate
change because it is tied to temperature, the hydrological
cycle, and the surface energy balance. Some regional studies
Figure 11·8. Lower tropospheric Arctic temperature trends (°C per decade,
January 1979 to February 1996), as monitored by MSUs on polar orbit-
have found evidence that a portion, but not all, of observed
ing satellites.
inter-annual snow cover fluctuations can be explained by
large scale (i.e., continental to hemispheric) forcing. Preci-
pitation has increased in high latitudes by up to 15% over
11.2.2.2. Radiatively important trace substances
the last 100 years, most of which has occurred in the winter
Certain trace substances alter atmospheric radiative forcing
in northern latitudes within the last 40 years (Bradley et al.
through enhancement of the greenhouse effect or through
1987, Groisman 1991, Karl et al. 1993, Groisman and East-
scattering and absorption of solar radiation (e.g. aerosols
erling 1994, Dahlstrøm 1994, Hanssen-Bauer and Førland
and clouds). Records of these substances give an indirect
1994).
method of assessing climate change. Because of the rapid
Between 1988 and 1996, annual average snow cover
increase in its levels globally over the last two centuries,
extent was 24.4 million km2, significantly lower than the
carbon dioxide (CO2) has been the major focus of research
1972-1985 average of 25.9 million km2 (Figures 11·9 and
on effects of greenhouse gases on temperature. However,
11·10). The late 1980s and early 1990s saw a decrease in
CH4, N2O, H2O, O3, and CFC's, whether their sources are
spring northern hemisphere snow cover compared with the
in the Arctic or in the mid-latitudes, also contribute to the
previous 15 years, concurrent with warmer temperatures
greenhouse effect (Wang 1986). The question of long-term
(Groisman et al. 1994b). However, no trends in snow extent
changes in the composition of the Arctic atmosphere can
are evident, and spring snow covers during 1995 and 1996
only be addressed by continued monitoring of trace gases.
were as extensive as those observed in the earlier period
724
AMAP Assessment Report
Million km2
Million km2
10
35
34
9
33
8
32
31
7
30
6
29
5
28
27
4
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990 1992
1994
1996
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990 1992
1994
1996
Spring (northern hemisphere)
Summer (northern hemisphere)
Million km2
Million km2
23
49
22
48
47
21
46
20
45
19
44
43
18
42
17
41
16
40
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990 1992
1994
1996
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990 1992
1994
1996
Fall (northern hemisphere)
Winter (northern hemisphere)
Figure 11·9. Snow cover over northern hemisphere lands between 1972 and 1996 for different seasons. Values are determined from analyses of NOAA
snow charts created using visible satellite imagery. (D. Robinson, Rutgers University).
(Figures 11·9 and 11·10). Recently, several datasets com-
Million km2
prised of in situ station observations of snow cover have
10
been examined (Foster 1989, Cao 1993, Brown et al. 1995,
Hughes and Robinson 1996, Barry et al. 1995). Foster
8
(1989) noticed a trend toward earlier spring melt since the
late 1960s for much of the North American Arctic tundra.
6
Data on precipitation are difficult to collect due to the
high degree of spatial variability in precipitation (Willmott
et al. 1994, Willmott and Legates 1991). Gauges are sparse
4
and records are generally biased, underestimating precipita-
tion by over 50%. Satellite data, notably passive microwave,
2
when calibrated by snow survey information, may offer an
instrument for regional surveillance of the Arctic snow cover
(Ferraro et al. 1994, Robinson et al. 1993, Woo et al. 1995,
0
Grody and Basist 1996). However, the introduction of new
instrumentation for measuring precipitation may inadver-
- 2
tently affect monitoring efforts and obscure subtle changes.
Snow cover water equivalent measurements from satellite
are as yet unreliable (Armstrong and Brodzik 1995), but air-
- 4
borne gamma-measurements are promising (Carroll and
Carroll 1993, Carroll 1995).
- 6
Direct measurements of snow atop Arctic sea ice are rela-
1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996
tively scarce (Barry et al. 1993a). No reliable means are yet
Figure 11·10. Monthly snow cover anomalies over northern hemispheric
available for remote sensing of snow depth or snow liquid-
lands (including Greenland) between January 1972 and August 1995.
water-equivalent over sea ice. However, snow extent can be
Also shown are the 12-month running anomalies of hemispheric snow
inferred from changes in surface albedo. Snow retreats
extent, plotted on the seventh month of a given interval. Anomalies are
northward over the pack ice during June and July, and the
calculated from a mean hemispheric snow extent of 24.5 million km2 for
the full period of record.
ice is essentially snow-free by mid summer (Robinson et al.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
725
1992). Substantial inter-annual variability in rates of snow
ing used alone or in combination with longer records of ice
melt has been observed (Scharfen et al. 1987). Direct obser-
extent obtained from surface observations to detect and in-
vations of snow cover are too limited in space and time to
terpret possible trends or lack of trends (Parkinson and Ca-
document natural variability and trends.
valieri 1989, Mysak and Manak 1989, Gloersen and Camp-
Current general circulation models (GCM's) predict a
bell 1991, Parkinson 1992, Zwally 1995) and to identify
warming of 2-5°C and increased precipitation for Arctic
links to climate forcing (Cavalieri and Parkinson 1981, Ser-
environments in response to global climate change (Schle-
reze et al. 1990, Mysak et al. 1990, Power and Mysak 1994,
singer and Mitchel 1987, IPCC 1990a, 1996a), but predic-
Chapman and Walsh 1993, Serreze et al. 1995). The nega-
tions of future changes in summer and winter precipitation
tive anomalies in Arctic ice extent can be linked to changes
have large uncertainties. Most GCMs predict enhanced pre-
in atmospheric circulation, in particular to an increase in cy-
cipitation at high latitudes with an average increase of 20-
clonic activity in the Eurasian sector of the Arctic (Maslanik
25% over all seasons in North America (Mitchell et al.
et al. in press). The relatively short record of satellite obser-
1990, IPCC 1992a, Maxwell 1992).
vations and the large inter-annual variability in the sea ice
cover must be taken into account when assessing connec-
tions to climate change (Zwally 1995).
11.2.2.5. Hydroclimatology
Estimates of ice transport as measured by drifting buoys
Climatic warming and the increased melt of stored water
(Colony and Thorndike 1984, McLaren et al. 1987), ob-
will affect the present hydrologic balance with the likely di-
served from satellites (Emery et al. 1995), or simulated by
rect effect of raising the sea level globally. Although there
models (Walsh et al. 1985) are used to estimate mass budgets
are estimates of the general water balance of the Arctic, the
and possible connections between ice transportation and
detailed hydroclimatology of the Arctic drainage system is
changes in ocean salinity and circulation (Hakkinen 1993).
still insufficiently known (WWB 1974, Baumgartner and
No techniques are yet available to observe ice thickness or
Reichel 1975, Ivanov 1990, Ivanov and Yankina 1991).
the rate of change of ice thickness over large areas and ex-
There is a sharp decline in the number of basic meteorolo-
tended time periods (Table 11·1). Existing measurements of
gical stations as one progresses northward. Although dis-
sea ice thickness, while valuable for describing general con-
charge measurements (Global Runoff Data Center, Koblenz;
ditions, are insufficient for documenting changes over inter-
Roshydromet, St. Petersburg) are relatively much better than
annual or climatological time scales (McLaren et al. 1990).
those for climatic driving variables within the region, im-
Although areas of thinner ice have been recorded (Bourke
provements in the basic hydrometeorological data are neces-
and Garrett 1987, Bourke and McLaren 1992, McLaren
sary before assessing any further changes.
1989, Wadhams 1990), Walsh et al. (1995) found no appre-
ciable trend toward thicker or thinner ice over the North
Pole in the period 1958 to 1992. One problem is that sea ice
11.2.2.6. Sea ice
measurements taken by upward looking sonar (Vinje et al.
The responsiveness of sea ice cover to thermodynamical and
1989) provide average ice draft information within a sonar
transport processes suggests that changes in sea ice extent,
beam, but variations of the thinner and more fractured areas
concentration, thickness, and transport are sensitive indica-
that may be the most sensitive indicators of climate change
tors of climate change (Hall 1988, Barry et al. 1993b). How-
are not recorded. In addition to sonar data, airborne laser
ever, regional and inter-annual variability complicate the de-
profilers and electromagnetic induction sounding techniques
tection of a general climate-change signal. The extent of sea
have provided ice thickness estimates (Nagurny 1995).
ice has been lower than average during the 1990s (Johan-
Too little is currently known about the natural variability
nessen et al. 1995, IPCC 1996a), including reductions in
of Arctic sea ice thickness to draw any conclusions with re-
Arctic ice extent larger than those observed in the remote-
gard to climate change. Models suggest that warming tem-
sensing record through 1979 (Maslanik et al. 1996). Total
peratures will lead to substantial changes in sea ice extent.
mass of sea ice is a critical variable for determining possible
Simulations using coupled ocean-atmospheric models show
impacts of climate change on Arctic atmospheric and oceanic
that Arctic ice thickness decreases considerably when the at-
conditions. However, measurements of sea ice thickness are
mospheric CO2 content is increased (Manabe et al. 1992).
relatively rare and not suitably distributed in space and time
The postulated warming from CO2 could have important
to detect trends (McLaren et al. 1992). Characteristics such
consequences for the thickness and extent of Arctic sea ice
as ice age, salinity, and surface roughness provide some infor-
and consequently for the ice exported through Fram Strait.
mation about climatic conditions and interactions since growth
and decay of sea ice influence the temperature, circulation,
11.2.2.7. Vegetation
and moisture content of the overlying atmosphere, all of
which, in turn, affect sea ice mass (Polar Group 1980, IPCC
The Arctic troposphere is profoundly affected by the large
1990b, Meehl and Washington 1990, Raymo et al. 1990).
areas of vegetation which contribute to the strong seasonal
Relatively accurate ice extent and concentration informa-
cycle of trace gases seen in the Arctic. In addition to cycling
tion can be determined from satellites (Parkinson et al. 1987,
trace gases, vegetation affects surface albedo as well as soil
Thomas 1990, Maslanik and Barry 1990, Barry et al. 1993b,
temperature and moisture, thus playing an important role in
Weaver et al. 1987, Serreze et al. 1995). These data are be-
the energy balance and hydrological cycle.
Table 11·1. Various techniques used to date to measure ice thickness.
Technique
Applicability
Platform
Reference
Surface drilling through ice
Local surveys
Surface
Ackley et al. 1976, Kovacs 1983, Koerner 1973
Upward-looking sonar from mobile platforms Local, basin surveys Submarine, ROVs
McLaren 1989, Walsh et al. 1995, Wadhams et al. 1991
Upward-looking sonar from moored buoy
Local
Moored array
Moritz 1992
Laser profiler
Basin surveys
Aircraft
Krabill 1992, Comiso et al. 1991, Wadhams et al. 1991
Electromagnetic impulse sounders
Local surveys
Helicopter
Kovacs 1983
Satellite estimation of thin ice types
Basin surveys
LANDSAT, ERS-1 SAR, Radarsat Steffen and Heinrichs 1994, Steffen and Schweiger 1990
726
AMAP Assessment Report
Vegetation can also provide an indirect record of climate
concurrent sea level rise of about 15-30 cm (Revelle 1983).
changes. With warmer temperatures, the extent of boreal
Measuring changes of ice sheets in Antarctica and Green-
forest will probably expand and the treeline will move far-
land by conventional surveying methods is beyond present
ther north into regions that are currently tundra (Svein-
means. Satellite mounted radar altimeters can measure
björnsson et al. 1992). Tree ring studies can give a record of
changes in surface elevation of the ice sheets. The measure-
response to climatic conditions. At the northern edge of bo-
ments are not very precise, however, and await the launch of
real forests, trees exhibited a positive growth response during
a laser altimeter on future satellite missions such as EOS
the warming of the 1930s and 1940s, but not during the re-
(Earth Observing System). Present indications show that the
cent period of warming (Jacoby and d'Arrigo 1995). How-
mass balances of Greenland and possibly Antarctica are
ever, because of the influence of microclimates, growth pat-
positive, i.e. they are growing, not shrinking (Zwally 1989).
terns are idiosyncratic, making the interpretation of tree-ring
data difficult (Mason and Gerlach 1995).
11.2.2.10. Ice and sediment cores
The reconstruction of past climatic conditions from the sedi-
11.2.2.8. Soils and permafrost
mentary records of ice caps, lakes, ponds, and peats is an
Concern over the impacts of climate change and altered UV
important element of climate change research. These records
on soils is related to emission of greenhouse gases. Nadel-
offer time series that are typically one to three orders of
hoffer et al. (1992) highlighted the important differences in
magnitude longer in duration than the instrumented climate
response of dry, moist, and wet Arctic soils to changes in air
record, thus affording unique perspectives on long-term nat-
temperature and precipitation. However, accurate predic-
ural variability. This context is invaluable when attempting
tions of the effects these changes will have in soils are com-
to discern natural from anthropogenic climate forcing (IPCC
plicated by changes in vegetation and the additional effects
1996a). Paleoclimatic data are useful in validating how ac-
of other changes such as enhanced CO2, UV-B, and increased
curately climate models simulate climatic forcing; they pro-
atmospheric pollution. Soil temperatures are critical to ac-
vide a testing ground for how well the same models are
tive layer waterlogging, aeration, and nutrient cycling. Con-
likely to perform in predicting future conditions (Overpeck
sequently, soil temperature affects plant communities and
et al. 1991). It is generally recognized, however, that the
the balance of CO2 and CH4 emission.
forcing mechanisms of anthropogenic climate change, and
Permafrost is both an indirect indicator and an archive of
perhaps the rates of envisaged change, have no direct geo-
climate change because increases in air temperature can
logical analogs (Overpeck 1995, IPCC 1996b). Because an
thaw the soil. Permafrost terrains display evidence of previ-
understanding of the past is critical to predicting the future,
ous warm periods, such as the formation of thermokarst and
and because the historical perspective is a robust means to
deepening of the active layer during the Holocene climatic
decipher processes occurring on time scales from decades to
optimum in the western Arctic (Burn and Smith 1990). One
millennia, paleoclimatic studies are extremely useful, parti-
of the best examples of the impact of climate change comes
cularly in the northern high latitudes.
from northern Alaska where Lachenbruch et al. (1988) have
documented evidence of 2-4°C warming over the last 100
11.2.2.10.1. Ice cores
years based on an inversion in the upper part of several deep
ground temperature profiles. Indigenous residents of north-
Ice cores have been collected from several locations in the
ern Alaskan villages also report thawing of previously frozen
Arctic, providing reasonable geographic coverage for Green-
ground. While thermokarst is a natural part of the evolution
land and the Canadian Archipelago (e.g., Körner and Fisher
of permafrost landscapes and has been linked to forest fires
1990, Grootes et al. 1993). Ice cores are unequalled archives
rather than climate change (Burn 1990, Burn and Smith
of atmospheric gases and particulates. However, they are ex-
1990, Harry and MacInnes 1988, Mackay 1995), more re-
pensive to collect and analyze, and are restricted to stable ice
cent observations by Osterkamp (1994) have confirmed
masses. Paleotemperature indicators from ice cores include
warming and thawing of discontinuous permafrost in Alas-
stable isotopes of oxygen, borehole temperature profiles,
ka. Lewkowicz (1992) has also linked the high number of
and melt-layer frequencies. This information is used to de-
recent active layer detachments on the Fosheim Peninsula of
rive paleo-temperatures, as well as the thicknesses of annual
Ellesmere Island to unusually warm summer conditions.
accumulation corrected for ice flow, which are used to de-
rive past snow accumulation (Figure 11·11) (Alley et al.
1993, Alley and Anandakrishnan 1995, Cuffey et al. 1995).
11.2.2.9. Glaciers and ice sheets
Complementary indicators include aeolian sea salt, dust, bio-
Glacial history of the large Greenlandic ice sheet and of
genic sulfonates from the ocean, particulates from boreal
smaller glaciers throughout the Arctic provide both long-
forest fires, volcanic ash, and geochemical proxies of solar
and short-term evidence of climate change. Historical re-
activity (e.g., Mayewski et al. 1993, Stuiver et al. 1995, Tay-
cords and photographs often include the size of glaciers;
lor et al. 1996, Saltzman et al. in press).
these can be used to infer changes. Because the length of a
Although ice core records offer outstanding resolution for
glacier is tied to snowfall, which in turn is tied to tempera-
the last glaciation and the Holocene, ice compaction and flow
ture and other factors, moraine positions provide evidence
compromises the record of the previous interglacial period
of warming and cooling episodes. Indications of global
(Grootes et al. 1993). Air bubbles in ice cores are a source of
warming from glacier length are consistent with, but inde-
information on paleo-chemistry of atmospheres. Analysis of
pendent of, other records of global warming during this
the trapped air reveals gradual atmospheric changes on the
century (Oerlemans 1994).
glacial-interglacial time scale that are linked to variations in
Increased temperatures can cause glaciers to melt, but can
Earth's orbital parameters. More than 20°C of warming, for
also cause increased precipitation. The balance of these two
example, are inferred since the coldest portion of the last
processes determines the net storage of water in glaciers and,
glacial period (Figure 11·11) (Cuffey et al. 1995). A greater
thus, whether sea levels will rise. Over the last 100 years,
contribution of the ice core record, perhaps, has been to-
glaciers have receded globally, contributing to part of the
ward understanding the character and rates of abrupt climate
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
727
18O ()
Temperature °C
changes, unrelated to external (orbital) forcing, that occur-
red during the last glaciation and toward its termination.
- 34
Examples include the documentation of Heinrich/Bond
- 30
events, with roughly 7000 year periodicity, that are related
to surges of the Laurentide Ice Sheet from Hudson Bay (Bond
- 36
et al. 1993), as well as the millennial Dansgaard/ Oeschger
- 35
oscillations linked to changes in oceanic thermohaline circu-
lation (Broecker et al. 1990). Further, ice cores have been in-
strumental in demonstrating that 1) abrupt climate changes
- 38
- 40
may occur on time scales relevant to humans (Figure 11·12)
(Dansgaard et al. 1989, Alley et al. 1993); 2) large changes
are not restricted to ice ages, but may equally affect the rela-
- 45
tively warm interglacial climate state (Dansgaard et al. 1993,
- 40
O'Brien et al. 1995); and 3) there are strong global telecon-
nections of several discrete paleoclimatic events (Bender et
- 50
al. 1994, Brook et al. 1996).
- 42
- 55
11.2.2.10.2. Paleoecological records
0
10
20
30
40
Unlike in ice cores, the climate signal is not recorded directly
Thousands of years before present
in the paleoecological record. Instead, plant and animal fos-
sils preserved in sedimentary deposits provide a record of
Figure 11·11. History of temperature changes in central Greenland over
the last 40 000 years, from the GISP2 core, showing very large and prob-
past climatic conditions. The prevalence of lakes and ponds
ably abrupt changes (after Cuffey et al. 1995). The stable-isotopic ratios
throughout much of the Arctic enables the development of
of ice were calibrated, as shown on the vertical scales, using borehole
relatively dense networks of coring sites. Over broad geo-
temperatures in the ice sheet. The record shows a warming of more than
graphic areas, the time-transgressive nature of climatic and
20°C since the coldest time of the last ice age, and jumps of many °C
over decades.
ecological changes may be determined. This is particularly
Ice accumulation
depth (m)
m/y
1 600
1 700
1 800
0.3
0.2
0.1
Preboreal (PB)
Younger Dryas (YD)
Bolling/Allerod (BA)
Oldest Dryas (OD)
0.0
10 000
11 000
12 000
13 000
14 000
15 000
16 000
17 000
0.3
0.2
0.1
0.0
11 590
Year before present
11 690
12 860
Year before present
12 960
14 620
Year before present
14 720
25-year smoothed
3-year change
Figure 11·12. History of snow accumulation in central Greenland during the most recent glaciation, as measured in the GISP2 core (after Alley et al.
1993). The 25-year running mean, represented in all panels, shows very large and rapid climate changes. Shorter-term variability is shown in the lower
panels. Age is relative to present = 1950. Accumulation doubled at the end of the Younger Dryas cold event, as shown in the middle-lower panel, and a
somewhat larger change occurred almost as rapidly at the onset of the Bolling warm event.
728
AMAP Assessment Report
relevant in the Arctic where regional variations in the north-
1991, 1992, 1996) and the Hudson Bay area (Catchpole
ward transport of heat by the atmosphere and oceans cause
1992). Additional investigations could yield climate recon-
spatial heterogeneity and strong latitudinal gradients in cli-
structions for other areas such as Arctic Russia and Siberia.
mate. Palynology is the paleoecological technique that has
Traditional ecological knowledge and especially oral his-
been most frequently applied to climate reconstructions
tory provide a further source of climate information from
(Bartlein et al. 1986, Prentice et al. 1991). However, paly-
the recent past. Elders, as oral historians, often have good
nology has some limitations in many Arctic regions (e.g., the
memories of environmental changes that have occurred since
High Arctic), owing to the low pollen production rates of
their childhood and may know stories related to them by an
many local tundra plants, and the related over-representa-
earlier generation. Potentially useful sources of climate in-
tion of exotic pollen types of uncertain, distant provenances
formation might come from traditional knowledge and oral
(Gajewski et al. 1995). Plant macrofossils (seeds, leaves,
history studies, yet little work has been done in this area.
buds) extracted from lake and peat cores have the advantage
Archaeologists are frequently able to integrate a variety
of testifying with certainty the past presence of plant taxa.
of research methods to provide a long-term perspective on
Unfortunately, rich macrofossil sites are not common in the
human-resource-climate interactions. Northern archaeology
Arctic, so that species representation may be selective and
has greatly expanded its field of interest to include zooar-
the record may be more strongly influenced by local edaphic
chaeology, paleobotany, human paleobiology and new meth-
factors than by climate. For sites with well preserved and
ods of relative and chronometric dating (McGovern et al.
diverse plant macrofossils, paleoclimatic inferences may be
1988, Mason and Gerlach 1995). An interesting recent de-
made with reasonable confidence (Birks 1991), especially
velopment is a desire among northern archaeologists, histo-
when coupled with co-occurrent fossil groups, such as in-
rians, and others working in related fields to combine their
sects (Elias et al. 1996).
knowledge and efforts to increase understanding of the rela-
The siliceous fossils of freshwater diatoms are ubiquitous
tionship between humans and climate change. An example
in the sediments of both lakes and ponds, and appear to re-
of this is the interdisciplinary work currently being under-
spond rapidly and sensitively to climatically controlled lim-
taken on the Norse settlements in Greenland (Buckland et
nological changes (Smol et al. 1991, 1995, Pienitz and Smol
al. 1996, Barlow et al. 1997).
1993, Pienitz et al. 1995). Although recent advances have
been made in Arctic freshwater diatom ecology (Douglas
11.2.3. Ability to predict
and Smol 1995, Wolfe 1996a), many regions remain under-
studied. The rigorous application of diatom-based paleolim-
Computer models based on physical principles help under-
nology to the study of climate change in the Arctic is there-
stand the Earth's climate and assess the prospect of climate
fore still in its infancy, although progress is being made. For
change. A variety of classes of models are in use today,
example, Douglas and Smol (1994) have documented dra-
enabling the study of various components of the climate.
matic diatom stratigraphic changes, believed to be climati-
Coupled General Circulation Models (CGCMs) are the most
cally induced, in the sediments deposited over the last 200
sophisticated of these, consisting of sub-models of the atmos-
years in ponds on Ellesmere Island. These results, and others
phere, ocean, cryosphere, and land surface. Assessment of
in progress, clearly demonstrate the strong potential of paleo-
climate change requires consideration of each component of
limnological approaches toward addressing questions of cli-
the climate system, and CGCMs are therefore the most pow-
mate change in Arctic regions.
erful tools available for this purpose. CGCMs have devel-
One of the most significant advances in paleoecology has
oped rapidly in the 1990s (IPCC 1996a), but there remain
been the improvement of sediment dating control through
problems that must be resolved before they can be used to
direct 14C measurements by accelerator mass spectrometry
confidently project regional climate change. Simulation of
(Andrée et al. 1986). Very small samples of plant remains, as
the Arctic climate is particularly challenging, in part because
well as selectively extracted organic compounds (e.g., humic
of the extreme sensitivity of the models to sea ice.
acid) may now be dated with confidence to about 40 000
In recent years climate modelers have begun to work more
years. Most Arctic lakes are typified by low sediment accu-
closely by comparing the results of their respective models, a
mulation rates relative to their temperate counterparts, so
process that helps to identify systematic model errors (cf.
that the ability to date specific levels, instead of increments
Walsh et al. 1995, Tao et al. 1996). Over the Arctic Ocean,
of core several centimeters thick, becomes especially relevant
the mean bias of 19 models simulating surface air tempera-
(e.g., Snyder et al. 1994).
ture compared with observations was found to be small
Due to the complex glacial history of the Arctic, most
(< 1°C), except in spring when it was +3°C. This springtime
continental sediment records are limited to the Holocene
bias may be sufficient to prematurely break-up the Arctic ice
(the last 10 000 years), although longer records do exist in
in a coupled model if the bias persists over decades. The pre-
certain regions (Wolfe 1994, Elias et al. 1996). This in no
cipitation predicted by every CGCM studied was larger than
way detracts from the utility of these records for paleocli-
observed (Vowinckel and Orvig 1970, WWB 1974, Elliot et
mate research, since both warm (Overpeck 1996) and cold
al. 1991, Ross and Elliott in press), particularly during the
(Maslin and Tzedakis 1996) climate `surprises' are thought
winter months, when it was more than twice what is ob-
to punctuate the interglacial climate state, at rates relevant
served. Therefore, empirically derived climatologies contain
to humans.
large uncertainties. For example, although evaporation in
winter was found to be excessive, in summer the simulated
evaporative flux did not differ substantially from observa-
11.2.2.11. Historical and archaeological evidence
tions. The freshwater flux (precipitation minus evaporation)
Documentary historical records can provide information
was approximately twice that observed, suggesting that the
about past variations in climate, the impact of climate on
models' input of freshwater to the Arctic Ocean was too
past societies, human responses to climatic stress, and hu-
large. Walsh et al. (1995) point out that this may have im-
man perceptions of climate and climate change (Ingram et
portant implications for the stratification, stability, and dy-
al. 1981). In the Arctic, historical records have been used to
namics of the Arctic Ocean in coupled model simulations.
reconstruct past climate in, for example, Iceland (Ogilvie
The simulated total cloud cover in the Arctic was found to
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
729
vary tremendously from one model to the next. During the
tion in the North Atlantic would have a direct impact on cli-
summer, for example, the cloud cover was found to vary
mates throughout the rest of the world.
from 30% to more than 90%. Finally, in most models the
The principal waters entering the Arctic Ocean are the
snow depth of Greenland was not in equilibrium, because in
relatively warm and saline waters from the Atlantic via
each successive year of a 10-year simulation there was more
Fram Strait and the Barents Sea and the relatively fresh wa-
snowfall than the sum of evaporation and melting.
ters from the North Pacific via Bering Strait. These waters
From the studies of Walsh et al. (1995) and Tao et al.
flow in a counterclockwise direction around the four major
(1996) it is clear that state-of-the-art atmospheric models
basins where they are subsequently modified by air/sea/ice
do not adequately simulate the present Arctic climate.
interactions, river inflow, and exchange with surrounding
Improvements in models will be necessary before they can
shelf regions. The large volume of relatively fresh water
produce credible predictions regarding future temperatures,
stored in the upper 200-300 m of the Arctic Ocean reflects
circulation patterns, or consequent ozone concentrations.
inputs from river inflow, sea-ice melt, net precipitation, and
Efforts are underway to more closely study CGCM simula-
the inflow of Pacific water (Aagaard and Carmack 1989,
tions and improve the understanding of coupled model sim-
Treshnikov 1985, Macdonald and Bewers 1996).
ulations. Further development of atmosphere, ocean, cryo-
Underneath the surface mixed layer is a cold isothermal
sphere, and land surface models are all high priority efforts
layer with markedly increasing salinity called the Arctic
in the climate community, as it is clear that advancements in
halocline. This halocline layer overlies warm Atlantic water,
each are vital to the development of the coupled climate
and inhibits convection, which would otherwise release heat
models used to understand the prospects of climate change
from the Atlantic layer and hinder ice formation in the Arc-
in the polar regions.
tic (Aagaard et al. 1981, Melling and Lewis 1982, Wallace
et al. 1987). The halocline is weaker in the eastern Arctic
than in the western Arctic which is more strongly affected
11.2.4. Components of the Arctic
by low-salinity Pacific waters. Thickness and horizontal ex-
The Arctic climate system is one of the most complex and
tent of the halocline layer also affects the areal extent of sea-
dynamic climate systems on the earth. The strong interac-
ice cover, and thus has direct implications for climate. Re-
tions between various components make understanding the
cent observations suggest that the boundary between these
Arctic, and therefore predicting future changes, extremely
two regimes may move across ridge systems in the vicinity of
complex. Each component is dynamically tied to the other
the Lomonosov Ridge (McLaughlin et al. 1996).
components through energy, water, and trace gases exchange.
Salinity distributions dominate the density structure with-
in the Arctic Ocean, and thus determine the large-scale ther-
mohaline flow (Aagaard et al. 1985, Coachman and Aagaard
11.2.4.1. Oceanic regime
1974, Semtner 1987, Hakkinen 1993). Pathways of flow are
The Arctic Ocean influences global climate change through
created by salinity-dominated buoyancy fluxes (both positive
its effects on surface heat balance and thermohaline circula-
and negative) around the basin perimeter (Gawarkiewicz
tion in the Arctic Basin (Aagaard and Carmack 1994). Both
and Chapman 1995). Fresh water components, such as
processes are closely linked to the salinity structure and sea
brackish seawater and ice, exit the Arctic Ocean through
ice cover of the Arctic Ocean. The atmosphere-ocean ex-
Fram and Davis straits into the North Atlantic, where they
change of energy and matter, which is strongly modified by
may supply buoyancy to the upper ocean, slow the rate of
the presence or absence of sea ice, controls the flow of heat
deepwater formation, and thus impact the global thermoha-
and water vapor from low to high latitude regions. In addi-
line circulation by affecting rates of water mass transforma-
tion, the presence of sea ice and its associated snow cover
tion in the Greenland, Iceland, and Labrador Seas (Dickson
significantly affects the surface albedo and radiation budget.
et al. 1988, Aagaard and Carmack 1989). The thermohaline
Any discussion of climate change must include consideration
circulation is, in turn, responsible for as much as half of the
of salinity (cf. Rooth 1982), sea ice (cf. Lange et al. 1990),
Earth's poleward heat transport, affecting all aspects of
and the Arctic Ocean circulation (cf. Stigebrandt 1981, Aa-
global climate (Broecker et al. 1985a).
gaard and Carmack 1994).
The formation of deep water in the North Atlantic, and
more specifically in the basins of the Greenland, Icelandic,
and Norwegian Seas (Nordic Seas), is a major component of
11.2.4.1.1. Ocean stratification and water circulation
global oceanic circulation. This is one of only three places in
Water tends to evaporate in regions where temperatures are
the world's oceans where an exchange between warm, less-
high and condense in regions where temperatures are low.
saline water and deeper, more-saline water takes place. Thus,
For this simple reason, the cold polar oceans maintain fresh-
the existence and strength of this exchange has major conse-
ened surface waters floating over more saline deep waters.
quences for the world ocean and the marine biosphere, as
Through brine rejection, freezing serves to further separate
deep water formation enables entrainment and transport of
salt and fresh water, acting as the high-latitude counterpart
oxygen and nutrients to deeper parts of the world ocean.
to evaporation (Aagaard and Carmack 1989, Macdonald
The traces of this entrainment can be seen well beyond the
and Carmack 1991). This basic stratification acts to inhibit
equatorial region of the Atlantic.
thermally forced convection and thus is a dominant factor
The importance of deep water formation and related pro-
controlling ice cover, surface albedo, and material transport
cesses in the Nordic Seas goes beyond the oceanic regime. It
in high-latitude oceans. Changes in freshwater flux to the
also controls the strength and geometry of thermohaline cir-
oceans associated with melting ice and other environmental
culation in the North Atlantic and basically controls the
changes could trigger large and abrupt climatic changes
amount of warm water exported by the Gulf Stream to north-
(Broecker 1994, Alley 1995). Sea level rise of 1-2 mm per
ern Europe and into the Barents Sea. Thus, climate condi-
year in restricted and sensitive regions of the North Atlantic
tions in northern Europe depend on and may be changed by
from melting of land ice is nearly as big as the freshwater
alterations in deep water formation in the North Atlantic.
fluxes modeled to cause major reductions of deepwater for-
The convective processes in the Nordic Seas occur in dif-
mation (Rahmstorf 1995). Reductions in deep water forma-
ferent stable configurations, each of which is accompanied
730
AMAP Assessment Report
by significantly different climatic conditions in northern
with synoptic systems can significantly advect pack ice (e.g.,
Europe and the European Arctic. If, however, the condition
Dey 1980) at roughly 2% of the surface wind speed, pro-
of the warm water is changed, e.g. through a lesser salt con-
duce coastal polynyas (Pease 1987), and affect the organiza-
tent or even higher water temperature (an expected conse-
tion and fractional coverage of leads (e.g., Walter and Over-
quence of climatic warming), a major part of the convective
land 1993).
system in the Nordic Seas breaks down. This leads to a de-
crease in the magnitude of thermohaline convection, i.e. a
Leads and polynyas
decrease in warm water flow to the North Atlantic, and a
Leads and polynyas exert a prevalent and immediate effect
possible enlargement of the southward extent of sea ice.
on the surface energy balance as well as the hydrological
The balance leading to one or the other of the stable condi-
cycle. They are often locations of plankton blooms and feed-
tions is extremely fragile and can be considered as a `switch'
ing areas for marine mammals. Inuit continue to use both
for northern European climate. It is hypothesized that alter-
leads and polynyas for hunting marine mammals as they
ations in this balance in the past have led to short-term changes
have for the past three millennia (Schledermann 1980).
in regional climate such as that during the Younger Dryas.
Leads are long, roughly linear openings, or breaks, in the
pack ice caused by variations in the wind stress. They range
in width from a few meters to a few kilometers and in length
11.2.4.1.2. Sea ice
from a few kilometers to hundreds of kilometers. In the cen-
Sea ice is one of the defining properties of the Arctic oceans;
tral Arctic the areas of open water and thin ice, or the effec-
it affects the biosphere, human populations, the energy bal-
tive lead fraction, averages about 3% in the winter and
ance, and water vapor exchange between the ocean and the
spring, rising to 6% in the summer (Lindsay and Rothrock
atmosphere. The Arctic Ocean sea ice cover is a mass of dif-
1994). The effective lead fraction in the peripheral seas was
ferent amounts and concentrations of ice of various ages,
found to be between 5% and 10% in the winter, while in the
surface characteristics, and properties. It extends over about
summer the peripheral seas are often ice free. In the summer,
15
106 km2 of the ocean in winter but shrinks to 8
106
open water is much more prevalent, occupying as much as
km2 in summer (Gloersen et al. 1992). Regional variations
10% of the area in the interior of the pack, although there is
in open water within the sea ice cover contribute signifi-
little or no temperature differential between the ice and the
cantly to modifying ocean salinity (Martin and Cavalieri
open water.
1989) and heat and moisture fluxes into the atmosphere
The effect of leads on the surface energy balance occurs
(LeDrew et al. 1991).
due to the large difference in albedo between thick ice and
One of the major characteristics of sea ice in the polar
open water or thin ice in leads, and to the large contrasts
seas is its seasonal variation in thickness and extent. The an-
possible between lead surface temperatures and the overly-
nual cycle of sea ice growth and decay is a driver of tempera-
ing air. In winter, open water has a temperature of 1.8°C,
ture and salinity variations in the upper layers of the Arctic
as much as 40°C or more warmer than the surrounding ice
Ocean. The structure of sea ice largely reflects its evolution.
and atmosphere. The sensible heat flux from the open water
The presence of brine creates an ice microstructure which is
is high, and the open water in a lead often freezes within
very sensitive to temperature changes, resulting in large sea-
hours of the lead's formation. In the winter, the sensible heat
sonal variations within the ice that directly affect such prop-
flux changes sign, from roughly 10 or 20 W/m2 downward
erties as strength, thermal conductivity, albedo, microwave
over thick ice to as much as 500 W/m2 upward over open
emissivity and optical extinction (Weeks and Ackley 1982).
water with high winds (Andreas and Murphy 1986). The
For example, in midwinter leads, the brine released down-
sensible heat flux from leads is sometimes enough to change
ward from rapidly growing thin ice induces and intensifies
the sign of the regional-average sensible heat flux from a net
thermohaline circulation in the mixed layer (Carmack 1986);
downward flux to a net upward flux. In a warming climate
brine rejected upward toward the surface of the ice affects
this can have important ramifications in the structure of the
its brightness, temperature, and other microwave properties.
atmospheric boundary layer, which becomes unstably strati-
Sea ice modulates the energy exchange between the ocean
fied instead of being stably stratified (Serreze et al. 1992).
below and atmosphere above, effectively insulating the ocean
Cloud plumes originating from leads are often observed
from the atmosphere. Sea ice mass balance is determined by
in satellite images. Leads are a vast source of moisture for
calculating ice extent, concentration, thickness, and motion
the atmosphere. While they may not provide enough to in-
over time (Thorndike et al. 1992). The mass of sea ice con-
crease snowfall, they can significantly increase cloud cover.
tributes most of the fresh water supplied to the Greenland
An increase in effective lead area from climatic warming is
Sea and thereby impacts deep convection, bottom water for-
likely to increase cloud cover in the Arctic.
mation, and global thermohaline circulation. Climatic warm-
Polynyas are larger regions of thin ice or open water that
ing could lead to a decrease in both the thickness and the
occur repeatedly in similar locations throughout the polar
areal extent of sea ice, significantly affecting ocean heating
winter. Changes in air temperature will impact their size and
and the ocean-atmosphere heat flux at high latitudes.
location and the magnitude of their influence on ocean cir-
Changes in climate variables other than temperature can
culation, ice formation, and the energy balance. Polynyas
also directly act upon sea ice. Drag forces exerted by surface
are maintained by divergence in the ice drift or melt from
wind on the sea ice act upon atmosphere-sea ice interac-
oceanic heat flux, and they range in size from a few hundred
tions. Surface winds are mostly responsible for the smaller
square meters to hundreds of square kilometers (Smith et al.
scale motion of the sea ice cover, while large scale geo-
1990). Common locations are on the lee sides of islands or
strophic circulation patterns account for about half of the
peninsulas or at the edge of fast ice. In both cases, wind
large scale motion of sea ice; the other half is influenced by
blows the ice away from the open-water area, maintaining
ocean circulation (Thorndike and Colony 1982). The major
the polynya. The near-surface air temperature is much warm-
drift patterns of Arctic sea ice and its mean velocities are
er over the polynya than over the surrounding ice, yet much
characterized by a linear component (the Transpolar Drift)
colder than the surface water temperature. Thus polynyas
and a circular movement pattern (the Beaufort Gyre). On
will drive a strong sensible heat flux from the water that can
time scales of days, the winds and their changes associated
amount to a few hundred W/m2. Polynyas are large sources
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
731
of brine rejection caused by the high rates of ice production.
and on ocean circulation patterns. All of these processes will
This brine contributes to water-mass formation and ocean-
be affected by changes in climate. Changes to the Arctic have
current dynamics.
the potential to affect global climate through the response of
the Arctic trace gas and hydrologic systems.
Snow cover
Snow is an effective insulator that controls the rate of heat
11.2.4.2.1. Soil
conduction from the base to the surface of the ice and thus
affects ice growth rates (Maykut 1978). An increase in pre-
The soils of Arctic regions are particularly vulnerable to
cipitation, and thus snow cover, impacts not only ice growth
changes in climate because of the dominant role of tempera-
but also the surface energy balance. Fresh snow on sea ice
ture on their physical properties and biological processes.
increases surface albedo and further reduces any energy
Arctic soils are highly varied in pH balance, particle size,
transfer between ocean and atmosphere due to its low ther-
and moisture content. Because of the differing soil proper-
mal conductivity. In addition, snow may become part of the
ties, the effect of climate change varies considerably; while
sea ice cover through the formation of snow-ice, thus influ-
some responses will be large and rapid, others will be barely
encing the mass balance of the sea ice cover (Lange et al.
detectable. Depth of the active layer and the associated tem-
1990). The distribution of snow depth on sea ice is affected
perature and moisture regimes are the primary controls of
chiefly by sea ice topography, which is in turn a function of
processes of decomposition which determine the rate and
ice age and ice motion (Buzuev and Dubovtsev 1978). Snow
amount of organic matter accumulation and trace gas flux
depth measurements from the drifting ice stations of the
from soils. An increase in the depth of thaw and the length
Former Soviet Union indicate that the maximum snow depth
of the active season from warming temperatures will be neg-
on thick ice is in mid-May and averages 0.35 m. The snow
atively related to the moisture content (positively correlated
usually, but not always, disappears in July and August.
to the soil moisture deficit) (Nadelhoffer et al. 1992). Changes
Snow cover is a reservoir of fresh water and plays a key role
in moisture content are hard to predict because changes in
in melt pond formation.
precipitation are uncertain and soil moisture is also affected
by snow melt, drainage, and evapotranspiration. Moist and
Melt ponds
wet soils may become drier as a result of increased evapo-
The seasonal variation of the sea ice surface directly affects
transpiration and lowering of the water table.
the radiation balance and is one of the key elements of the
Soil moisture, to a large extent, determines the tempera-
ice-albedo feedback mechanism. A substantial portion of the
ture profile, depth of permafrost, and soil organic matter
sea ice is covered by dark melt ponds in the summer. This
content. Thermal conductivity, which is strongly regulated
lowers the albedo but does not substantially change the sur-
by the moisture content of the soil, is an important element
face temperature. The area of melt ponds reaches a maxi-
of soil/atmosphere temperature dynamics. Water has a lower
mum of 50-60% in early summer, and then decreases to a
thermal conductivity than air and organic soils have a ther-
minimum of about 10% at the end of summer, causing a
mal conductivity almost an order of magnitude lower than
strong seasonal contrast in the average surface albedo (May-
that of frozen, nearly saturated mineral soils (Kane et al.
kut 1986, Grenfell and Maykut 1977, Grenfell and Perovich
1992). Dry soils with cushion, heath, and lichen vegetation
1984, Perovich 1996). As the area of melt ponds increases,
and thin organic mats tend to occur on slopes or well drained
the area of lower albedo increases which leads to an increase
stony areas in the High Arctic. They have a relatively deep
in solar radiation absorption at the surface. However, later
thaw or active layer because of limited insulation by the or-
in the summer as the ponds warm and increase in size and
ganic layer and their high thermal conductivity. Moist soils
depth, they drain through the base and/or margins of the ice
constitute much of the patterned ground and tussock tun-
floes; consequently, total pond coverage decreases, increas-
dra, with low relief and moderate depths of organic matter,
ing albedo. Numerical, thermodynamic ice-growth models
which are typical of much of the low Arctic. The permafrost
show that the simulated ice thickness is sensitive to the frac-
is thinner in these soils because of insulation by the surface
tion of meltwater that runs off floes and to the melt pond
organic layer and high water content. Wet and waterlogged
coverage (Ebert and Curry 1993).
soils dominated by sedges and mosses occur in poorly drained
areas of the low Arctic. The thick organic layers which have
accumulated because of the waterlogged and anaerobic con-
11.2.4.2. Terrestrial regime
ditions insulate the soil and help to retain moisture, thus re-
The vast land masses of the Northern Hemisphere provide
ducing thermal diffusion and accounting for the shallow ac-
the Arctic climate system with a complex set of variables
tive layer.
that make climate change in the Arctic difficult to predict or
model. The land masses contribute warmer air to the polar
11.2.4.2.2. Permafrost
region, disrupting the polar vortex. Thus, the Arctic's atmos-
pheric dynamics and processes of climate change are dis-
Permafrost is `ground that remains at or below 0°C for at
tinctly different than those in the Antarctic. Soil and per-
least 2 years' (Permafrost Subcommittee 1988). It occurs ex-
mafrost dynamics affect trace gas fluxes, surface tempera-
tensively in Arctic and subarctic regions, affecting up to
tures, and the hydrological balance. Precipitation and runoff
80% of Alaska and 50% of Canada and Russia. Permafrost
influence ocean temperature, salinity, and circulation. Veg-
is divided into continuous and discontinuous zones defined
etation types and snow cover affect albedo and thus surface
by location and areal extent of cryotic ground. Depths range
radiation balance. Under a warming climate the terrestrial
from > 1000 m (1450 m in Siberia) to only a few meters
surface plays an important role in trace gas feedback effects.
near the southern limit (Heginbottom et al. 1993, Smith
Vegetation along with soil moisture and temperature affect
1993, Williams and Smith 1989). During the summer, the
trace gas fluxes and thus cause large seasonal differences in
surface of the ground thaws. The depth of this active layer
chemical atmospheric dynamics. Historically, terrestrial
ranges from a few decimeters in the High Arctic to more
ecosystems have stored CO2, helping to cool the Earth.
than 2 meters in parts of the discontinuous zone. The sea-
Glaciers and ice sheets have a large influence on sea level
sonal freezing and thawing of the active layer and the sea-
732
AMAP Assessment Report
sonal pattern of temperature change in the upper part of
prevails in those with greater thaw depths. Water balance
permafrost produce distinctive features unique to Arctic
dynamics, specifically run-off generation, evapotranspira-
tundra, such as patterned ground, gelifluction lobes, active
tion, and changes in soil moisture, are intimately connected
layer detachments, seasonal frost mounds, and frost cracks.
to permafrost dynamics. The most important factor control-
Permafrost reflects a thermodynamic balance between
ling evapotranspiration in the Arctic has been reported to be
ground surface temperature and the geothermal gradient.
soil moisture in the active layer (Kane and Hinzman 1988).
The spatial distribution and depth of permafrost are closely
Increase in active layer depth would simultaneously increase
related to climate and are expected to change with climate
infiltration, soil moisture, evapotranspiration, and the lateral
changes. Much extant permafrost is close to 0°C and inher-
redistribution of water through enhanced groundwater flow.
ently unstable. Thawing could cause the degradation of ex-
Woo and Marsh (1990) found that groundwater inflow into
isting discontinuous permafrost, a decrease in the distribu-
fen environments was also critical in maintaining soil mois-
tion of continuous permafrost, and potential terrain instabil-
ture during the summer. Rainfall run-off studies in the Arctic
ity (Smith 1993). There are serious concerns that there will
suggest that drainage basins underlain by permafrost main-
be increased erosion, mass wasting, disruption of surface
tain `flashier' stream hydrographs compared with non-per-
vegetation, and changes in surface drainage systems includ-
mafrost areas (Haugen et al. 1982).
ing drainage of critical wetlands (Fitzharris 1996). Perma-
Because meltwater is stored in the snowpacks, on the
frost degradation due to climate warming is complicated by
basin slopes, and within channels, the initiation of stream-
its effect on vegetation and potential increases in trace gas
flow often lags behind the commencement of snowmelt by
fluxes (Nisbet 1989); these changes could then create condi-
several days or more. Once the flow begins, it usually ex-
tions that would further affect climate.
hibits a marked diurnal rhythm, reflecting the daily snow-
Locally, the nature of the ground surface, including slope
melt cycle. In some instances, slush flow along a valley may
angle and aspect, surface water, vegetation, and snow cover,
convey water and snow rapidly downstream (Barsch et al.
creates boundary layer conditions that determine the degree
1993). Annual peak flows are common during this period
to which air temperature controls ground thermal regimes.
(Kane et al. 1992) and many rivers are prone to flooding.
Geologic, tectonic, and subsurface hydrologic conditions
After the snow is depleted in the basin, streamflow subsides
further influence permafrost.
except during some heavy rain events. Warming tempera-
The freezing of water in the ground produces an assort-
tures and ensuing thinner ice, increased precipitation, and
ment of ground ice forms ranging from disseminated ice
earlier spring melt could alter run-off dynamics and mean
crystals in a soil matrix (pore ice) to thick (10-20 m), hori-
residence times. The situation is far from straightforward,
zontally layered bodies of nearly pure ice which extend for
however, as increases in precipitation, also predicted by nu-
several square kilometers. The type and rate of permafrost
merous GCM's for the region between 50-70°N (IPCC 1990a,
formation involve a complex set of processes including soil
Boer et al. 1992a, 1992b), could enhance the formation of
particle size, temperature, water content and chemistry, and
saturation overland flow.
water transfer processes and rates. Ground ice content some-
times exceeds the saturated moisture content of its host sedi-
11.2.4.2.4. Snow
ments. When permafrost containing excess ice thaws, the
ground subsides in proportion to the volume of excess ice,
Because both the deposition and duration of snow on the
forming thermokarst.
ground during all seasons are associated with atmospheric
Of central importance in the investigation of ground ice
dynamics and thermodynamics, and high latitudes are be-
and climate change are the distribution, nature, and origin
lieved to be especially sensitive to global warming due to
of ice-rich permafrost and massive ground ice (e.g. Harry et
cryospheric feedbacks, snow cover fluctuations can poten-
al. 1988, Lawson 1983, Mackay 1992, Pollard and French
tially be used as an indicator of global climate change. Snow
1980, Pollard and Dallimore 1988). Few investigations have
cover changes the surface albedo, regulates surface tempera-
been made of massive ground ice in the Arctic Archipelago
ture, affects air mass formation, and insulates the ground
(French et al. 1986, Lorrain and Demeur 1985, Pollard
and vegetation from severe cold temperatures. The snow
1991, Barry and Pollard 1992), but considerable literature
cover-albedo feedback amplifies any climatic changes and
does exist for ground ice occurring in northern Russia. Of
impacts global climate variability (Cess et al. 1991, Randall
particular interest are studies on buried ice (Astakhov and
et al. 1994, Groisman et al. 1994a, 1994b). The huge differ-
Iasayev 1988), the gas content of ground ice (Arkhangelov
ence in albedo between snow cover and vegetation signifi-
and Novgorodova 1991), and ice petrography (Solomatin
cantly impacts the energy balance. The albedo of fresh snow
1986).
may exceed 0.80 and be as much as 4-5 times the value for
open water or tundra (Kondratyev 1969, Grenfell and War-
ren 1994). Inter-annual fluctuations of snow cover over the
11.2.4.2.3. Runoff
Northern Hemisphere, though much smaller than seasonal
The potential impacts on Arctic terrestrial water balance of
ones, are sufficiently large to affect global and regional ra-
elevated temperatures associated with the greenhouse effect
diative and thermal energy budgets (Barry 1985, Shine et al.
occur through the complex interactions of land surface hy-
1990). Snow contributes to the hydrologic cycle regionally
drology and the freeze/thaw cycle. Winter freezing of the
and globally and is a key element in ocean thermohaline cir-
active layer of permafrost as well as shallow groundwater,
culation (Broecker 1991).
lakes, and rivers inhibits the movement of water. During the
The insulation value of the snow is important to soil pro-
early thaw period, melting of snow above the frozen surface
cesses and to the winter survival of many species of plants
entrains and accelerates surface run-off of both water and
and animals. The accessibility of vegetation to herbivores is
constituents, with overland flow (not interflow or baseflow)
partly determined by the depth, density, and location of
serving as the dominant input into river systems (Kane and
snow, and thus snow affects their populations and distribu-
Hinzman 1988).
tion. A persistent increase or decrease in the extent, or a
Woo and Steer (1983) show that overland flow predomi-
change in the type, of snow cover could severely affect sur-
nates in sites with a shallow active layer, while infiltration
vival of vegetation and animals.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
733
plant photosynthesis (Figure 11·13). This process has re-
CO2
sulted in the tundra and boreal regions storing 14% of the
world's organic soil carbon. However, if the soils warm and
Cp
Cp
microbial activity increases, there is concern that much of
this carbon will be returned to the atmosphere in another
Cr
C
positive feedback by increasing the concentrations of the
r
greenhouse gas CO2.
The tundra has a high albedo compared with the neigh-
boring dark boreal coniferous forest or taiga. Changes in
species composition might greatly affect albedo and thus the
radiative balance. A northward migration of the tree line
would reduce albedo and provide a positive feedback to the
climate system, i.e., warming would encourage trees to re-
C
C
r
r
place the short tundra vegetation which would further de-
crease albedo and increase climatic warming. However, pol-
Nu
len records from the end of the last ice age indicate that
Cr
Nu
trees of the taiga move more slowly than the rates of pre-
D
D
dicted climate change. Possible feedback effects from a
MO
change in vegetation would be dampened by this lag. Per-
mafrost disturbance also affects plant species composition
and thus albedo.
The greatest change in Arctic ecosystems and thus feed-
MO
MO
backs to climate, should be expected where species are at
Active
Layer
their higher rather than lower temperature-related distribu-
DOC
LE
tion limits, i.e. at their southern and lower altitudinal bound-
aries, and where they are in proximity with potential com-
Permafrost (P)
petitors. The tundra/taiga ecotone is, therefore, a critical re-
gion of potential change.
Figure 11·13. Schematic illustration of ecosystem carbon fluxes and nutri-
ent circulation in the tundra (adapted from Callaghan and Jonasson 1995).
Carbon and nutrient pathways are shown by dashed and continuous lines,
11.2.4.2.6. Arctic glaciers and ice sheets
respectively. Atmospheric CO2 is fixed in the plants through photosynthe-
sis (C p). Dead parts of plants with organic carbon and nutrients fall to the
Glaciers and ice sheets are among the defining elements of
ground as litter and enter the decomposition cycle (D) where they are trans-
the Arctic. They are tightly coupled to climate change and
formed into soil organic matter. The organic matter with its nutrients un-
have been shrinking, contributing to sea-level rise; positive
dergoes complicated transformations in the soil microbial biomass (MO).
Carbon is continuously lost to the atmosphere as CO2 through microbial
feedbacks associated with global warming will accelerate
and plant respiration (C r) and made available directly for plant photosyn-
this melting of fresh water. Glaciers also play a role in global
thesis or added to the atmospheric pool (CO2). Nutrients are circulated
radiation balance and are an important `climate archive'.
within the microbial system of the soil or traded-off and taken-up by the
plants (Nu). Microbial activity is limited by, among other things, low tem-
Land ice in the Arctic includes the massive Greenland ice
peratures due to permafrost (P). Some carbon and nutrients can be lost
sheet and smaller ice caps and glaciers. The Greenland ice
from the system as dissolved organic matter (DOC) or nutrient leachate
sheet covers 1.7
106 km2, or 80% of the island of Green-
(LE) and transported to adjacent systems. Climate change acts on the sys-
land; an additional 0.1
106 km2 of the island is under smal-
tem mainly by controlling the rate of CO2 uptake by plants, and the activ-
ity of micro-organisms. Tundra ecosystems differ from others in that the
ler ice caps and glaciers. Ice cover in other areas of the Arc-
cold soils have large stores of nutrients and carbon, and the microbial bio-
tic (including coastal Alaska) amounts to almost 0.4
106
mass has low rates of CO2 uptake, i.e. low productivity.
km2 (Meier 1984).
Glacier mass is tied to precipitation and temperature.
Warming will cause most glaciers to recede. Many models
11.2.4.2.5. Terrestrial ecosystems: Physical properties
assume that, for the Greenland ice sheet, warming will pro-
The terrestrial ecosystems of the Arctic currently cool the
duce both increased melting at low altitudes and increased
Earth in three basic ways: by reflecting incoming radiation
snowfall at high altitudes, the latter linked to increased satu-
from high-albedo surfaces such as snow and ice; by exchang-
ration vapor pressure (e.g., IPCC 1996a). However, paleocli-
ing energy and water with the atmosphere; and by taking
mate records do not show much dependence of high-altitude
CO2 out of the atmosphere and storing the carbon in organ-
accumulation on temperature (e.g., Cuffey and Clow in
ic soils and peats. Terrestrial ecosystems will respond to cli-
press). A change in mass balance will produce a time-lagged
matic changes, resulting in positive feedbacks to the atmos-
change in ice flow and glacier extent. Glaciers which termi-
phere through mechanisms such as alterations in the balance
nate at tideline can advance over long distances as a func-
of trace gas emissions, particularly CO2 and methane; al-
tion of submarine moraines (Powell 1990). It is possible that
tered albedo as vegetation cover increases and forest extends
climate changes can influence maintenance of a glacier on its
into tundra areas; and plant responses to UV and enhanced
protective moraine. Run-off from glaciers that grow should
CO2. The net result of the array of feedback effects may be
increase due to summer melting. Eventually, however, tem-
positive or negative; overall effects remain inconclusive be-
perature increases will lead to glacial recession.
cause of the complexity of the many interactions.
A compilation of studies (Meier 1993) suggests that a
For approximately the last 10 000 years, many tundra
global warming of 1°C will lead to 1 mm per year of sea-
terrestrial ecosystems have taken carbon out of the atmos-
level rise from small ice caps and glaciers, with the Arctic
phere, reducing the natural greenhouse effect, because the
supplying over half of the total, and an additional 0.3-0.4
respiration of CO2 (dry habitats) and CH4 (wet habitats)
mm per year contributed from the Greenland ice sheet (IPCC
from soil microbial respiration during the decomposition
1990a). Over longer time scales (a century or more) the
cycle is slower than the uptake of atmospheric CO2 in green
small glaciers will shrink as the ice melts. The total volume
734
AMAP Assessment Report
of ice in smaller glaciers is not known with high accuracy
Temperature
due to a scarcity of thickness measurements, but it is probab-
The cold polar night is a dominant characteristic of the Arc-
ly enough to raise sea level 0.3 m if melted (IPCC 1996a).
tic climate. Indeed, the Arctic is often defined solely in terms
Long-term persistence of warming of more than 3°C is pre-
of low temperature, i.e. as that area where the average tem-
dicted to cause the Greenland ice sheet to shrink and split
perature for the warmest month is below 10°C. Temperature
into northern and southern domes. Warming of more than
disparities in the Arctic, between oceans and continents,
6°C, a plausible value, is predicted to remove the ice sheet
across latitudes, and between seasons, are complex. The
entirely over 10 000 years (Letreguilly et al. 1991). The
contrast between summer and winter climates in the interior
2.6
106 km3 of water in the ice sheet, plus up to an addi-
land masses of the subarctic is particularly extreme. For ex-
tional 0.1
106 km3 in smaller glaciers on Greenland, would
ample, Verkhoyansk, Siberia recorded an absolute January
raise global sea level over 7 m if completely melted.
low of 67.8°C and a summer high of 36.7°C. Steep tem-
The residence time (how long typical snowfall spends in
perature inversions characterize the Arctic boundary layer in
the ice, obtained by dividing the volume of the glacier by the
winter; these inversions are particularly strong over land.
input rate) averages a few centuries for the ice caps and gla-
Air temperatures over the sea ice cover tend to be warmer
ciers of the Arctic, but several thousand years for the Green-
relative to continental temperatures in the winter and a near
land ice sheet. Because glaciers are controlled by the physical
constant 0°C in the summer. The uniform and relatively
processes of ice motion as well as by snowfall and melting,
warm winter temperature is maintained by a balance be-
changes in glacier size typically lag climatic changes (by
tween the net radiation, which amounts to about 30 W/m2,
years to decades for typical mountain glaciers), and record
and the conductive flux and sensible heat flux, which aver-
smoothed versions of any change (see Paterson 1994). The
age about +15 W/m2 each (Maykut 1982). In the summer,
Greenland ice sheet typically responds much more slowly to
the strong positive net radiation, 80 W/m2 in July, is mostly
climate change than other ice masses in the Arctic. If climate
balanced by melt.
change is amplified in polar regions as expected (IPCC 1990a,
Air temperatures over the winter pack ice are colder near
1992a, 1996a, Cuffey et al. 1995), Arctic glaciers will have
the Canadian archipelago than on the Siberian side of the
a greater influence on the global water balance than esti-
Arctic Ocean. The ice-free regions in the peripheral seas
mated here.
warm above freezing in summer, depending on location and
local wind and ocean current regimes. In the winter these
areas are covered for the most part by thin, first-year ice, re-
11.2.4.3. Atmospheric regime
sulting in both warmer surface temperatures and more leads.
The atmosphere, along with the oceans, directly ties the Arc-
Strong horizontal temperature gradients are observed near
tic environment to the rest of the world. Atmospheric trans-
the ice edge where there are large variations in the surface
port of trace gases, including greenhouse gases, aerosols,
fluxes and surface temperatures, depending on whether the
and water, directly affects the Arctic environment. Many of
wind flows on or off the ice (Overland and Guest 1991).
the observed changes to the atmosphere are anthropogeni-
The diurnal cycle influences air temperature in the spring,
cally driven and it may, to some extent, be possible to con-
summer, and fall seasons except near the Pole where the sun
trol them through international agreements. The effects of
maintains a constant height above the horizon. Synoptic-
atmospheric changes on the Arctic are particularly strong
scale variations, with periods between 2 and 8 days, domi-
because of positive feedback processes.
nate the air temperature variability, except in summer when
fluctuations are small. The winter air temperature is strongly
correlated with cloud cover and wind speed. In the winter,
11.2.4.3.1. Atmospheric structure and components
the air temperature is an average of about 9°C warmer
The troposphere is the lowest portion of the atmosphere and
under cloudy skies than under clear skies, and 1.2°C warmer
is where the interaction with the surface and the ocean/land
for every meter per second increase in the wind speed.
interactions are most dynamic. The troposphere can be di-
The temperature increase caused by stronger wind speeds
vided into the boundary layer, which is close to the earth's
is due to breakdown of the low-level temperature inversion
surface, and the free troposphere, where the exchange of
through mixing. This increase in temperature with altitude is
gases with the stratosphere can be important. The atmos-
a characteristic feature of the polar boundary-layer climate.
pheric boundary layer contains moisture, trace gases, and
Primarily driven by radiation deficits at the surface and warm
aerosols from localized sources and is characterized by rapid
air advection aloft, the inversion typically extends to alti-
circulation. The height of the boundary layer in the Arctic
tudes of 1 km over the Arctic Ocean, with temperature dif-
can range from a few meters to a few kilometers. The bio-
ferences of 10°C. It is strongest during winter, although a
sphere is immediately affected by processes and constituents
secondary peak exists during the late summer due to melting
in the boundary layer.
at the ice-air interface. The seasonal and inter-annual vari-
The stratosphere, roughly 10-30 km above the earth's
ability in the Arctic inversion layer has been reported in sev-
surface, is the portion of the atmosphere where most of the
eral studies (Serreze et al. 1992, Skony et al. 1994, Kahl et
total column ozone is located. The dynamic nature and
al. 1996).
chemical composition of the stratosphere exert a major in-
fluence on ozone concentrations and are extremely impor-
Surface winds
tant to climate change. The stratosphere is less affected by
Surface winds are an important climatic parameter because
local sources and sinks of gas and is therefore more sensitive
of their influence on ambient temperatures, as well as en-
to global emissions than the troposphere. At higher levels in
ergy, trace gas, and humidity fluxes. Longer period changes
the Arctic stratosphere, the cooling effects of both ozone de-
in atmospheric circulation, including both air temperature
pletion and greenhouse gas increases should be clearly evi-
and winds, drive variations in sea ice extent (Rogers and van
dent against the background of natural variability. In the
Loon 1979, Walsh and Johnson 1979, Walsh and Sater 1981,
Arctic winter, stratospheric flow is dominated by extensive,
Fang and Wallace 1994). The surface stresses at the airice
and more or less circumpolar, cyclonic systems. These sys-
interface are communicated to the water and ultimately are
tems are referred to as the `polar vortices'.
responsible for the gross aspects of the basin-wide circula-
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
735
tion and local transports, such as through Bering Strait (Aa-
ranges from 40 to 70% (Vowinckel and Orvig 1962, Husch-
gaard et al. 1985). Surface winds tend to be suppressed with
ke 1969, Gorshkov 1983, Warren et al. 1986, 1988); the
clear skies, and stronger (closer to geostrophic) during cloudy
greatest cloud cover is found over the Atlantic side of the
conditions due to the effects of downwelling longwave radi-
Arctic Ocean where cyclonic activity is most frequent and
ation on boundary layer stability.
water vapor is relatively abundant (Serreze et al. 1995).
The northern boundary of the westerlies lies at about
Cloud cover is typically more limited over land, sea ice cov-
70°N, but even in a general sense an `Arctic high' and `polar
er, and the central Arctic Ocean, areas where water vapor is
easterlies' are only weakly indicated and, compared with
less abundant, the lower boundary layer is more stable, and
mid-latitudes, circulation is generally sluggish. Vowinckel
anticyclonic atmospheric conditions are common (Shine et
and Orvig (1970) report typical wind speeds of 4-5 m/s over
al. 1984, Serreze et al. 1993). Convective clouds (cumulus
the central Arctic, with greater speeds more common at the
and even cumulonimbus) are fairly common in winter over
periphery, especially at the exits of storm tracks from mid-
the open waters of the Norwegian and Barents seas.
latitudes. Seasonal and geographical variations in the Arctic
Total cloud amount increases to 70-90% in summer, with
sea-level pressure and wind fields show that cyclonic systems
the most rapid increase between May and June. Extensive
are relatively strong and prevalent in the Norwegian and
low-level, optically-thin Arctic stratus prevail over the ocean
Barents Seas in winter, and are more uniformly distributed
when relatively warm, moist air moves over the melting sea
and weaker in the summer (Serreze and Barry 1988, Walsh
ice cover and cold water and condenses (Herman and Goody
and Chapman 1990, Serreze et al. 1993). Anticyclones are
1976). An increase in cyclonic activity over the central Arc-
prevalent over Siberia, Alaska, the Yukon, and central Arctic
tic Ocean in summer is associated with increases in pole-
during the winter, and along the margins of the Arctic Ocean
ward water vapor transport and vapor flux convergence
during the summer. The spring and fall transition seasons
(Serreze et al. 1995).
generally feature high pressure near the pole and more fre-
There are still significant gaps in the understanding of
quent, anticyclonic circulation centers in the western Arctic.
cloud formation and maintenance in the Arctic (Moritz et al.
Significant temporal variations occur in the seasonal
1993). Related to this are uncertainties in assessing the im-
mean winds. Variability on time scales of a few days is domi-
portance of surface and advective fluxes of moisture through
nated by transient cyclones and anticyclones, and their asso-
open water. These uncertainties make it difficult to predict
ciated fronts (e.g., Shapiro et al. 1989). Higher wind speeds
climate change in the Arctic.
are found with cyclones or fronts; these storms either mi-
grate into the Arctic from lower latitudes or develop locally
11.2.4.3.2. Radiatively important trace substances
from generally baroclinic processes (LeDrew 1985, 1988).
Anomalous atmospheric conditions within the Arctic have
Changes in the atmospheric concentrations of a few trace
been attributed to both variations at lower latitudes, e.g.,
gases (CO2, CH4, H2O, N2O, CFCs, and ozone) and aero-
modulations in the Aleutian and Icelandic lows (Agnew
sols can strongly influence changes in the global energy bal-
1993), and to anomalous boundary forcing due to sea-ice
ance. These gases contribute to greenhouse warming in vari-
within the Arctic (Mysak et al. 1990). Interdecadal trends
ous ways. While some of them are emitted and absorbed in
for the Arctic include the tendencies for a decreasing inten-
the Arctic, most of the changes in mixing ratios of these
sity of the Siberian anticyclone during winter (Sahsamano-
gases are due to changes in anthropogenic activity at lower
glou et al. 1991), and an increasing frequency for cyclones
latitudes. The atmospheric cycles of many of the radiatively
and anticyclones north of 65°N throughout the year (Ser-
important trace substances are affected by the hydroxyl rad-
reze et al. 1993) which will affect the mean winds and their
ical (OH), which is the result of complex atmospheric chem-
variations.
istry involving production by ozone photolysis and destruc-
GCM simulations indicate that warming may cause re-
tion by reaction with CH4, CO, and a host of atmospheric
duced sea-level pressure in the Arctic (e.g., Gregory 1993)
trace substances (e.g., non-methane hydrocarbons). Changes
which will combine with a poleward shift in the mid-latitude
in the Arctic climate are likely to alter the trace gas balance
baroclinicity and storm tracks (e.g., Hall et al. 1994) to
within the Arctic and thus directly affect global climate.
cause more cyclonic storm systems, especially in the winter.
The Arctic peatlands, boreal forests, and permafrost con-
This implies more variability in the day-to-day winds, but it
tain potentially important sources of trace gases which could
is not certain whether there would be any systematic changes
amplify the effects of warming. The 7.5 million km2 Arctic
in the intensity of storms or in the typical strength of winds.
region holds a vast store of carbon in the soil, mainly in the
The present Arctic climate is punctuated by inter-annual to
wetlands which cover about 1.5 million km2 north of 60º.
decadal scale variations of substantial amplitude. These var-
This store represents the imbalance, accumulated over thou-
iations will probably continue and at any particular time
sands of years, between carbon fixed annually by plants in
their effects on atmospheric circulation and surface winds
net production and that released back to the atmosphere as
are liable to outweigh the slow changes associated with cli-
CO2 and CH4 through decomposition. The balance of the
matic warming.
processes of production and decomposition and of CO2 and
Understanding of surface winds in the Arctic is hindered
CH4 emission are strongly influenced by climatic factors and
by sampling problems and a scarcity of observations. In
may have an important effect on greenhouse gases. Evidence
principle, wind speed and direction can be derived from the
indicates that the Arctic Ocean currently contributes an in-
sea-level pressure field. Given the geostrophic flow, the sur-
significant amount of CH4 to the atmosphere yet stores larg-
face wind depends on the surface roughness and on the at-
er concentrations under the polar ice cover.
mospheric boundary layer structure, especially the vertical
The dominant environmental controls over fluxes of
profile of static stability (e.g., Overland 1985).
water, energy, and trace gases from Arctic ecosystems vary
seasonally, often changing completely from summer to win-
Clouds
ter. Soil and vegetation may be a source or a sink of CO2 in
Clouds have a strong impact on the energy and hydrologic
summer but are a net source in winter (Oechel and Vourlitis
balance of the Arctic. Even small changes in cloud cover can
1994), while CH4 flux is a summer phenomenon. Winter
alter the radiative balance. Total cloud cover during winter
variations in energy budgets are determined by slope and
736
AMAP Assessment Report
aspect as well as by albedo, whereas summer energy budgets
tion and its release to the atmosphere is controlled by soil
are governed by evapotranspiration, which also governs run-
moisture and vegetation type so that processes which deter-
off in rivers.
mine plant community composition influence methane re-
Trace gas and energy fluxes also change with spatial
lease (Whalen and Reeburgh 1990a, 1990b). Soils may also
scale. At the plot scale, vegetation type, nutrient availability,
consume methane through methane oxidation: there is in-
and moisture are important predictors. At the landscape
creasing evidence that the large areas of dry and mesic High
scale, moisture and hydrology, as governed by slope and as-
Arctic tundra may form a significant sink for methane (Chri-
pect, are the major controls. At the regional scale, tempera-
stensen et al. 1995).
ture and vegetation become the dominant controls. Moisture
Present information suggests that the Arctic Ocean has
has opposing effects on the two major trace gases: CH4 flux
only a minimal impact on the global methane budget (Kven-
declines with soil drying while CO2 flux initially increases
volden et al. 1993, Lammers et al. 1995). Methane concen-
(Reeburgh 1985).
trations in Alaskan waters which freeze over in winter are 3
to 28 times greater than in Canadian near-surface waters
Carbon dioxide
where the methane is approximately in equilibrium with the
Globally, carbon dioxide concentrations have increased by
atmosphere (Kvenvolden et al. 1993). The surface water un-
almost 30% since the late 18th century. Most of this increase
der the polar ice cover is supersaturated with methane that
has been attributed to combustion of fossil fuel, cement pro-
usually exceeds the atmospheric equilibrium concentration
duction, and land use changes. Continued increase of CO2 is
by factors of about 1.3 to 4.0. The polar ice cap, however,
expected due to continued anthropogenic activities.
forms a barrier to the atmosphere (Kvenvolden and Loren-
Ecosystems in the Arctic store large amounts of carbon
son 1995). These differences in oceanic methane concentra-
in soils that turn over very slowly. Global warming could
tions suggest that methane builds up in water when ice is
be exacerbated by the loss of stored carbon emanating as
present and is released to the atmosphere when ice is absent.
CO2 from terrestrial ecosystems. Interactions between car-
Because methane is released in the Arctic from coastal wa-
bon and nutrients (nitrogen, phosphorus) are a major con-
ters over a very short time period each year, it adds to the
straint on the carbon balance of all ecosystems, including
seasonal methane cycle and may have some regional impact.
the Arctic (Shaver et al. 1992). Increased soil temperature
and increased decomposition are likely to increase annual
Carbon monoxide
emissions of CO2 and reduce the proportion of carbon emit-
Carbon monoxide, while not a greenhouse gas, plays an im-
ted as CH4. Other important factors affecting CO2 release
portant role in the chemistry of the lower atmosphere large-
are more subtle climatic changes such as cloudiness and the
ly because of its reaction with the hydroxyl radical (OH), a
diurnal temperature range.
strong oxidant which controls the distributions of many
Schlesinger (1977) estimates the amount of carbon stored
chemically-reduced species. There is an inverse relationship
in tundra (and alpine) soils and in boreal forest soils com-
between the concentrations of these two molecules, such
bined is equal to 166 ppm of CO2 in the global atmosphere.
that high levels of CO tend to deplete OH and high levels of
For comparison, the pre-industrial atmosphere contained
OH deplete CO (Logan et al. 1981).
280 ppm of CO2, and the total cumulative amount of fossil
The greatest CO mixing ratios in the background atmos-
fuel carbon released to the atmosphere through 1995 is equi-
phere are found in the high latitudes of the northern hemi-
valent to 118 ppm of CO2 (Keeling 1994, Marland et al. 1994).
sphere. CO mixing ratios in the Arctic boundary layer have
Raich and Schlesinger (1992) summarized data on soil
a well-defined seasonal cycle, with the highest levels (200-
respiration rates and found positive correlations between
250 ppb) observed in late winter/early spring and lowest lev-
respiration, precipitation, and annual mean and seasonal
els (80-90 ppb) found in summer (Novelli et al. 1992).
temperature. An increase in temperature was correlated with
This distribution of CO in the Arctic is determined by
a median increase of CO2 flux of 9% per degree (Raich and
both natural and anthropogenic processes. CO has a long
Schlesinger 1992). If warming is accompanied by increased
lifetime in winter and high concentrations of man-made pol-
precipitation, respiration would be boosted further. On the
lutants found in the Arctic during winter are the result of
other hand, primary productivity is also positively correlated
their transport from the northern mid-latitudes (Khalil and
with both temperature and precipitation. Net carbon uptake
Rasmussen 1983a, Rahn and Lowenthal 1986). In summer
by ecosystems depends on the difference between production
the lifetime of CO in the Arctic is shortened because OH
and respiration.
levels increase; CO decreases until August, after which it
starts to increase again. The hydroxyl radical is responsible
Methane (CH4)
for the removal of many climatically-significant trace gases
Methane is a radiatively active trace gas that has been in-
in addition to CO, including dimethyl sulfide, methane, and
creasing in concentration at a rate of about 0.9% per year
the HCFCs (replacements of the CFCs). Thus, changes of
for at least the past 100 years (Khalil and Rasmussen 1983b,
CO levels in the atmosphere are expected to have an impact
Steele et al. 1987, Blake and Rowland 1988), although re-
on Arctic climate and global trace gas budgets.
cently the rate has decreased to 0.5% per year (Steele et al.
1992). On a per molecule basis, CH
Nitrous oxide (N
4 exerts a greenhouse
2O)
forcing that is an order of magnitude stronger than that of
N2O is an important greenhouse gas because of its long at-
CO2 (Shine et al. 1990). Sources of atmospheric methane are
mospheric lifetime and a radiative forcing larger than CO2
primarily located outside of the Arctic and include wetlands,
on a per-molecule basis. Global levels of N2O continue to
rice paddies, ruminants, biomass burning, gas production
rise in the background atmosphere. The main natural source
and transmission, termites, landfills, coal mining, and gas
of N2O is emission from the oceans and from wet soils
hydrates (Khalil and Rasmussen 1983b, Cicerone and Orem-
where N2O is produced by bacterial activities; the main an-
land 1988). However, the Arctic tundra is a potential source
thropogenic sources are from fertilizers in the cultivation of
of methane and there is concern that if the soil active layer
soils. The mean tropospheric mixing ratio of N2O was about
increases, CH4 may increase through the microbial produc-
310 ppbv in 1992 (WMO 1994), with an annual increase of
tion of methane. The relationship between methane produc-
about 0.8 ppbv per year over the past four decades (IPCC
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
737
1994). Over the past decade, annual increases ranging from
the atmosphere will be able to hold more water vapor, and
0.5 to 1.2 ppbv per year have been observed (Khalil and
increases in water vapor will cause additional regional warm-
Rasmussen, 1992). The main (and the only quantified) sinks
ing. Water vapor is difficult to measure at cold temperatures
of atmospheric N2O are photolysis and reaction with O(1D)
and atmospheric monitoring often does not address it.
in the stratosphere. A possible sink of tropospheric N2O is
The Intergovernmental Panel on Climate Change (IPCC)
uptake by soils (Donoso et al. 1993).
(1990a) stated that GCMs show that an increase in humid-
Understanding the correlation between N2O and NOy is
ity will parallel an increase in warming under a doubling of
particularly important for the investigation of the budget of
CO2. However, data show a decrease in precipitable water
the nitrogen family and also for the identification of denitri-
from the surface to 500 mb over northern Canada (Elliot et
fication in the Arctic winter (Kondo et al. 1994, 1996).
al. 1991). More recent analyses show that 20-year trends of
Denitrification has a very strong influence on the chemistry
relative humidity are positive for North America but nega-
of stratospheric ozone destruction in the polar region (Fahey
tive at 500 mb in interior Alaska and northern Canada; at
et al. 1990a, 1990b, Loewenstein et al. 1993, Kawa et al.
the same time, the dewpoint in Canada and Alaska is in-
1992b, Oelhaf et al. 1995, Nakajima et al. 1996). Correla-
creasing (Ross and Elliot et al. in press). These seemingly
tions between N2O and ozone have been used by several in-
contradictory results emphasize the need for improved cli-
vestigators to infer chemical ozone loss in the Arctic (Proffitt
mate models and continued measurements in the Arctic.
et al. 1990, Manney et al. 1994a, Bregman et al. 1995).
Due to its long photochemical lifetime, N2O can be used
Aerosols
as a tracer to study vertical and horizontal transport in the
Aerosols in the troposphere have the potential to modify cli-
stratosphere. A series of in situ measurements of N2O in the
mate by perturbing the earth's radiative balance (Wigley
polar Arctic vortex has been used to investigate the mor-
1989, Charlson et al. 1992). Climate forcing can occur di-
phology of N2O distribution (Schmidt and Khedim 1991,
rectly as a result of particulate scattering and absorption of
Loewenstein et al. 1990), both with respect to the position
solar radiation, or indirectly as a result of aerosol-induced
relative to the polar vortex (Podolske et al. 1993) and with
changes in the prevalence, location, and albedo of clouds.
respect to time (Bauer et al. 1994). These studies show the
The removal of these atmospheric particles by deposition to
descent of N2O-poor air inside the polar vortex and a strong
snow and ice has the potential to then influence climate by
gradient of N2O across the vortex boundary.
alteration of the surface albedo. Averaged over the entire
northern hemisphere, the annual direct forcing due to sulfate
Chloroflourocarbons (CFCs)
aerosols has an estimated value of about 0.5-1.0 W/m2,
Chloroflourocarbons (CFCs) are direct greenhouse gases;
which is similar in magnitude but of the opposite sign to the
their contemporary radiative heating amounts to about 10%
forcing by current levels of all anthropogenic greenhouse
of the global total of radiative forcing from all anthropo-
gases combined (Charlson et al. 1991).
genic gases (IPCC 1996a). CFCs also influence the atmos-
The absorptive black carbon component of aerosols is
pheric energy budget indirectly because they affect the abun-
much more effective in altering the atmospheric energy bud-
dance of stratospheric ozone, particularly in polar regions.
get in the Arctic than elsewhere due to the high albedo of
The flux of CFCs to the atmosphere from Arctic terrestrial
the Earth's surface in the Arctic. In the period March to
sources, however, is negligible in comparison to sources
May, these aerosols have a net positive radiative forcing
from mid-latitudes (McCulloch et al. 1994). The direct ef-
(Blanchet 1989, 1991). This is opposite to the net effect of
fect of CFCs on ozone concentrations are dealt with in sec-
these aerosols on a global basis. Thus, there are large spatial
tion 11.3.2.
and temporal gradients in aerosol forcing associated with
With the exception of very small quantities from volcanic
aerosols over northern, high albedo areas (i.e., the Arctic
vents, these substances are present in the atmosphere as a re-
and much of the continents), and these need to be addressed
sult of human activity (Isodorov et al. 1990). CFCs are re-
in climate change studies.
moved from the atmosphere by photolysis in the stratos-
Natural aerosols in the Arctic include terrestrial dusts,
phere so that tropospheric concentrations are governed by
marine salt particles, ice crystals, smoke particles, and bio-
mass transport to the stratosphere and the rates of removal
genic particles. Aerosols from major volcanic eruptions such
there (WMO 1994). The decrease in the anthropogenic
as El Chichon or Mount Pinatubo are important to the Arc-
CFCs produced and emitted since 1990 is reflected in stable
tic and are transported predominantly in the stratosphere
or decreasing levels (Simmonds et al. 1996, UNEP 1994).
while small, local volcanic eruptions are transported in the
This has the effect of reducing the range of concentrations
troposphere and are less important.
close to the global mean value, particularly in remote loca-
Aerosols in the Arctic are of climatic importance because
tions such as the Arctic.
of their relatively long tropospheric lifetimes (Ogren and
Recent calculations show that the direct radiative heating
Charlson 1983). The comparatively low levels of precipita-
from CFCs is, to an extent, offset by indirect effects arising
tion and low mixing ratios of water vapor in the High Arctic
from their interaction with stratospheric ozone (Ramaswa-
mean that particles are unlikely to be scavenged by precipi-
my et al. 1992, Daniel et al. 1995, Solomon and Daniel
tation or to absorb atmospheric water and grow to sizes con-
1996). The magnitude of the indirect effect is liable to be
ducive to rapid settling. Typically, aerosol concentrations in-
larger toward the poles, since the greatest ozone losses are
crease in the winter and early spring when northern mid-lat-
observed in the polar stratosphere. The major concern for
itude pollution sources are strongest, meteorological condi-
the Arctic is the extent to which polar stratospheric ozone
tions are favorable for aerosol transport into the Arctic, and
depletion offsets local greenhouse enhancement.
the lower troposphere is extremely stable. Components of the
springtime aerosol maximum, known as Arctic haze (Shaw
Water vapor
1995), reach concentrations similar to those found in popu-
Water vapor affects greenhouse warming, particularly be-
lated mid-latitude regions (Rosen et al. 1981), a remarkable
cause it absorbs strongly in the infra-red. This is especially
finding considering the sparse population of the Arctic.
important in the Arctic where humidity is low due to cold
In the Arctic, winter and springtime aerosols have a ma-
temperatures. As the air temperature of the Arctic increases,
jor anthropogenic component, probably originating in the
738
AMAP Assessment Report
mid-latitudes (Barrie et al. 1981, Ottar 1981, Rahn 1981,
Average ozone mixing ratio
ppbv
Lowenthal and Rahn 1985). Summer and fall aerosols
600
show generally lower overall concentrations, have a smaller
anthropogenic component, and contain relatively more nat-
ural aerosols (Lannefors et al. 1983). March-April anthro-
500
pogenic aerosol levels may have followed a statistically-sig-
nificant decrease from 1982 to 1992, hypothesized to result
300 - 100 mb
from a reduction in pollution emissions (Bodhaine et al.
400
1993, 1995). Others, however, challenge these conclusions
(Jaffe et al. 1995). Increasing aerosol concentrations are
suggested (Barrie et al. 1988) as a possible explanation for
winter and spring surface cooling (Finlayson-Pitts et al.
300
1990), via an intensification of the atmospheric dehydration
cycle (McConnell et al. 1992).
The presence of one aerosol type can influence the preva-
lence of another. For example, ice crystals are not typically
80
present in Arctic haze. One explanation is that the haze
aerosols, composed largely of sulfate and sulfate coated par-
70
500 - 300 mb
ticles, de-activate scavenging ice-forming nuclei (Clarke and
Noone 1985, Borys 1989). Consequently, clear sky precipita-
60
tion increases, and the airmass dehydration rate is acceler-
ated. Fewer activated particles also increase the lifetime of
50
700 - 500 mb
the aerosol, cooling surface temperatures (Blanchet and Gi-
rard 1994, 1995, Bradley et al. 1993), causing cold anom-
alies exceeding 2°C over the ice covered Arctic Ocean, and
40
strengthening the surface temperature inversion by about
+ 4°C during fall and winter over the last 40 years (Kahl et
surface - 700 mb
al. 1993a, 1993b). This is contradictory to the effects of
greenhouse gases alone.
30
A modest amount of carbonaceous aerosol (0.2-0.6 mg/m3)
increases diabatic heating (0.1-0.2 K per day) when com-
pared with the effects of water vapor (Valero et al. 1988).
Atmospheric warming is further enhanced by reflected visi-
surface
ble light from the snow covered surface. Temperature profile
analyses (Kahl et al. 1993a, 1993b) indicate a springtime
20
warming tendency in the lower troposphere of the High Arc-
tic. In parallel, early model simulations estimate a spring-
time warming of 1-2°C (Blanchet 1989). Model simulations
1980
1982
1984
1986
1988
1990
1992
indicate that the excess heat produced by soot aerosols will
Figure 11·14. Trends in (annual average) ozone mixing ratio over Canada
increase temperature but will also preferentially alter the
from 1980 to 1993 (from Tarasick et al. 1995).
surface energy balance, snow and ice cover, and regional
scale circulation. According to Kahl et al.'s (1993a, 1993b)
the upper troposphere, ozone acts as a greenhouse gas, trap-
results, this amount of warming is marginally significant
ping infrared radiation that would otherwise escape to space,
given the natural variability of temperature in the Arctic.
leading to heating of the lower atmosphere. In the lower tro-
Another potential influence of tropospheric sulfate aero-
posphere, ozone is a pollutant and acts as a poison to both
sols is a role in hosting chemical reactions that lead to tro-
plants and animals.
pospheric ozone destruction. There is evidence that reser-
Evidence from vertical profile measurements of ozone in
voirs of acidic chlorine and bromine compounds that are in-
the Arctic suggests that the stratosphere is an important
active in ozone destruction are converted to active chlorine
source of ozone to the upper and middle troposphere (Bro-
and bromine gases on sulfuric acid aerosols (Barrie et al.
well et al. 1992, 1994, Oltmans et al. 1989b, Raatz et al.
1994, McConnell et al. 1992).
1985, Bachmeister et al. 1994). Tropospheric ozone has a
Large uncertainties in the magnitude of, and strong spa-
spring maximum (except in the boundary layer over and
tial gradients in, aerosol forcing make it crucial that aerosol
near the frozen Arctic Ocean) and an autumn minimum.
influences be actively represented in climate models, rather
The spring buildup may have more than one source, al-
than simply represented as a passive anti-greenhouse influ-
though the late winter and spring maximum of ozone in the
ence (Charlson et al. 1992). The results of Wigley and Raper
lower stratosphere probably contributes substantially to the
(1992) indicate that the neglect of anthropogenic particles in
peak in the troposphere (Oltmans 1991). A strong low-level
GCMs will result in an uncertainty in temperature projec-
temperature inversion and proximity to the Arctic Ocean
tions for the Northern Hemisphere in the year 2050 of
determine the distribution of ozone in the troposphere.
about 2°C.
The significant decline in ozone in the lower stratospheric
reservoir over the past decade may reduce tropospheric ozone
Tropospheric ozone
levels, since in recent years a decline in tropospheric ozone
Ozone in the Arctic troposphere comprises roughly 5-10%
parallels that seen in the lower stratosphere. Though the tro-
of the total overhead burden of atmospheric ozone. Despite
pospheric trends (Figure 11·14) have not been mechanisti-
this relatively small percentage, tropospheric ozone (usually
cally linked to the stratospheric decline, the parallel nature
below about 8-10 km in the Arctic) plays a key role in both
of the changes is clearly suggestive. In polar regions, combi-
the chemical and radiative behavior of the atmosphere. In
nations of cold winter temperatures, aerosols, and long per-
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
739
iods of darkness and sunlight facilitate the chemical alter-
cade: long-term trends have been measured, and short-term,
ation of ozone. These chemical processes combine with
geographically isolated events of extremely low ozone levels
transport regimes that may either incorporate ozone pre-
have been observed. Some studies have confirmed the impor-
cursors into polar latitudes or mix ozone from the stratos-
tance of halogen chemistry in the destruction of the ozone
phere into the troposphere.
layer; however, the causes and the magnitude of recent changes
Episodes of very low tropospheric ozone observed during
in Arctic halogen processes are not completely understood.
the spring in the Arctic Ocean basin are unique (Barrie et al.
Recent, unusually cold stratospheric temperatures and changes
1988, Oltmans et al. 1989b). Shortly after the appearance of
in circulation patterns have also been cited as important fac-
sunlight over the frozen Arctic Ocean, ozone concentrations
tors in observed low ozone concentrations. Despite the po-
have been measured at near zero for up to a few days (Olt-
tential impact on the environment and humans, little scien-
mans et al. 1989a). At the onset of these episodes a strong
tific effort has been made to understand the changes in the
inverse correlation was noted between ozone and atmos-
Arctic stratospheric ozone layer.
pheric bromine (Barrie et al. 1988, Oltmans et al. 1989a).
Most of the ozone in the atmosphere is in the `ozone lay-
This ozone depletion has not been observed inland from the
er', a region of the stratosphere between 10 and 30 km above
Arctic Ocean or at sites where the ocean remains open dur-
the earth's surface. Because ozone is the major absorber of
ing the winter (Oltmans and Levy 1994, Barrie et al. 1994).
near-UV radiation in the stratosphere, it helps determine the
The bromine that plays a key role in the ozone loss is of bio-
temperature structure of the stratosphere and thus affects at-
genic origin and is emitted through leads in the ice (Sturges
mospheric circulation processes. Stratospheric ozone is de-
et al. 1993). The exact mechanism of the ozone-bromine reac-
stroyed by heterogeneous chemistry involving chlorofluoro-
tion has not been established, but may involve heterogeneous
carbons (CFCs) and other ozone-depleting substances in re-
chemical reactions as in the stratosphere (McConnell et al.
actions that are facilitated by the occurrence of extremely
1992). Ozone replenishment from above is prevented by a
low stratospheric temperatures at the end of winter when
strong temperature inversion which keeps air trapped near
the molecules are energized by the return of sunlight. The
the surface (Mickle et al. 1989) and limits the impact of bio-
unique temperature and dynamics of the Arctic atmosphere,
genic bromine on the higher levels of the Arctic troposphere.
in combination with chemical processes, contribute to great-
Local sources can also add to the ozone concentrations
er ozone loss in the Arctic than at mid-latitudes.
in the troposphere. Forest fires over Canada produce ozone
Predictions for future quantities of ozone in the Arctic are
enhancements within the plume (Browell et al. 1994, Ander-
unreliable due to a lack of understanding of photochemical
son et al. 1994). In areas with a large population or indus-
and dynamical processes forming the Arctic atmosphere
trial activity, local ozone production might be expected
(WMO 1994). Since the 1994 WMO report, further reduc-
when sufficient sunlight and ozone precursors are available
tions in the Arctic ozone layer have been observed, and quest-
(Jaffe 1991). The effect of fire- or industrially-produced
ions remain concerning the observed changes.
ozone on ozone distribution within the Arctic is expected to
be small. Mauzerall et al. (1996) suggest that during sum-
11.3.2. Chemistry of ozone depletion
mer the largest source of tropospheric ozone below 5 km is
Polar vortex dynamics
dispersed, in situ photochemical production.
A great deal of scientific effort has gone into understanding
the physical and chemical processes contributing to the Ant-
arctic ozone hole. Less is known about processes of Arctic
11.3. Arctic stratospheric ozone
ozone depletion because, while similar in its general climate,
Changes in stratospheric composition have been observed
the Arctic does not form a distinct seasonal ozone hole. This
in both the Arctic and Antarctic polar regions. Changes in
is primarily due to the instability of the Arctic polar vortex,
stratospheric temperature, aerosol concentration, and ozone
a consequence of larger land masses in the northern middle
concentration are important to the energy balance of the
hemisphere than in the southern middle hemisphere. The vast
Arctic as well as to the UV which reaches the biosphere.
land area leads to greater land-sea temperature contrasts and,
Upper-air measurements may offer clearly discernible rela-
hence, more planetary-scale waves that disturb the northern
tionships to such phenomena as global warming due to the
polar vortex and result in frequent major stratospheric warm-
enhanced greenhouse effect and to the effects of ozone de-
ing. In Antarctica, the lowest ozone depletions are observed
pletion. At higher levels in the Arctic stratosphere, the cool-
inside the polar vortex, with clear indications that hetero-
ing effects of both ozone depletion and greenhouse gas in-
geneous chlorine and bromine chemistry is the dominant
creases should be clearly evident against the background of
factor behind ozone deviations (WMO 1994). The strong
natural variability. Measurements of change in these upper
polar winds in the Antarctic isolate the air masses, allowing
atmospheric layers, in combination with quantities observed
them to reach much cooler temperatures than are observed
at the surface, provide an ensemble of information to give
in the Arctic. In the Arctic, the picture is more complex be-
the most robust opportunity for climate change detection.
cause the dynamic exchange of air masses across the Arctic
In the Arctic winter, stratospheric flow is dominated by ex-
vortex does not allow for cooling as severe within the Arctic
tensive, and more or less circumpolar, cyclonic systems.
vortex as is observed within the Antarctic vortex. Neverthe-
This flow is referred to as the `polar vortex'. The coherence
less, anomalously low ozone levels have been observed in
of these polar vortices determines the exchange of stratos-
the Arctic during the last decade.
pheric air between lower latitudes and the Arctic.
Both concentration and distribution of ozone in the Arc-
tic stratosphere have undergone changes in the 1990s (Taa-
las 1993). Some of these changes may be linked to aerosols
11.3.1. Arctic stratospheric ozone
from the eruption of Mount Pinatubo, but some of the loss
Ozone is an important trace gas in the earth's atmosphere
observed in the Arctic has been attributed to halogen chem-
because it blocks harmful UV radiation from reaching the
istry. Halogen containing compounds, primarily chlorine ox-
biosphere and it acts as a greenhouse gas. Significant changes
ide (ClO), chlorine nitrate (ClONO2), hydrogen chloride
have occurred in the Arctic ozone layer during the past de-
(HCl), bromine oxide (BrO), and bromine nitrate (BrONO2),
740
AMAP Assessment Report
Table 11·2. Total column ozone measurement stations a.
larly significant in the stratosphere over the South Pole dur-
ing the austral spring, where ozone depletion is constrained
Toron-
Year
Longi-
within the Antarctic polar vortex, leading to the ozone hole.
to data- measure-
Lati-
tude, °
base
ments
Location
Location
tude,
(negative,
They are potentially more important in the Arctic region be-
St. no.
started
name
country
°N
if west)
cause of the high level of biological activity in the Arctic
which would be directly affected by increased UV radiation.
005
1957
Dikson Island
Russia
73.50
80.23
018
1957
Alert
Canada
82.50
62.30
Reductions of over 40% have been observed in the winter
024
1957
Resolute
Canada
74.72
94.98
stratosphere at high northern latitudes (SESAME 1995). The
042
1957
St. Petersburg
Russia
59.97
30.30
impact of these reductions in ozone on UV radiation and its
043
1952
Lerwick
UK
60.13
1.18
051
1952
Reykjavik
Iceland
64.13
21.90
effect on biological systems are not yet fully understood.
052
1943
Tromsø
Norway
69.65
18.95
089
1990
Ny-Ålesund, Svalbard Norway
78.93
11.88
105
1963
Fairbanks
USA
64.82 147.87
11.3.3. Measurements of stratospheric ozone
114
1974
Heiss Island
Russia
80.62
58.10
117
1961
Murmansk
Russia
68.97
33.05
Ground-based, airborne (such as balloon and aircraft), and
118
1962
Nagaevo
Russia
59.58
150.78
satellite instruments are used to monitor ozone and supply
123
1973
Yakutsk
Russia
62.08
129.75
129
1973
Pechora
Russia
65.12
57.10
data to determine ozone trends in the stratosphere. Some in-
140
1990
Thule
Greenland 76.52
68.76
struments monitor only total atmospheric ozone, while oth-
142
1973
Igarka
Russia
67.47
86.57
ers measure ozone profiles with varying degrees of vertical
144
1973
Markovo
Russia
64.68
170.42
resolution and range. The ground-based Dobson network,
145
1974
Olenek
Russia
68.50
112.43
148
1973
Vitim
Russia
59.45
112.58
used for measuring total ozone above the location of each
150
1974
Mansijsk
Russia
60.97
69.07
instrument, was first established in 1958 (Dobson 1968a).
165
1946
Oslo
Norway
59.91
10.72
Today, data from about 50 stations are used for analyzing
186
1975
Tiksi
Russia
71.58
128.92
189
1970
Hornsund, Svalbard
Norway
77.00
15.55
global trends in ozone (Bojkov et al. 1995a) (Table 11·2).
Since the late-1970s, satellites have been used to measure
a. Total column ozone levels have been measured for the past several de-
ozone globally. Many of these satellites are not appropriate
cades in or near the Arctic. Despite their importance for scientific re-
search and long-term monitoring, many of these stations are under
for Arctic research, however, because of limited latitudinal
threat of being shut down due to budget considerations. The data from
range or dependence on sunlight (Miller 1989, WMO 1988).
these stations are available from the World Ozone and UV Data Center
Satellite measurements have helped advance understanding
in Toronto, Canada.
of both dynamical and chemical processes that determine
appear to be most important. Cold temperatures and polar
the distribution of stratospheric ozone. The satellite instru-
stratospheric clouds or aerosols found in the Arctic activate the
ments listed in Table 11·3 use several different techniques
halogen chemical processes that facilitate ozone destruction.
to measure ozone in the stratosphere. Not all of the satellite
Stratospheric halogens arise primarily from anthropo-
instruments are appropriate for year-round monitoring of
genic emission of chlorine- and bromine-containing sub-
the polar ozone layer. Two satellites presently in orbit con-
stances in the troposphere. These CFCs do not react in the
tain ozone monitoring equipment appropriate for the Arctic.
troposphere and are transported into the stratosphere. This
The Global Ozone Monitoring Experiment (GOME) on
transport occurs primarily across the tropical tropopause
ERS-2 satellite, launched in 1995, takes measurements of
and can take 2-3 years (Schmidt and Khedim 1991). The
Arctic ozone daily. The EarthProbe satellite, launched in
CFCs then circulate toward the polar regions and to higher
1997, also has a Total Ozone Mapping System (TOMS) in-
altitudes in the stratosphere, where they are photolysed by
strument aboard.
ultraviolet radiation (SORG 1987). CFCs photolyse as they
pass poleward: the stratospheric concentration of CFC-11,
11.3.4. Results of measurements
for example, at 20 km is 10-20% of that in the troposphere
(Fraser et al. 1994). CFCs can also act as tracers: the shape
A variety of analyses of ozone data have shown a decrease
of the CFC-12 concentration profile has been used by Not-
in Arctic ozone over the past three decades, most of which
holt (1994) to show the subsidence of stratospheric air dur-
has occurred since 1980. Results from some of these analy-
ing winter above Ny-Ålesund, Spitsbergen.
ses are summarized in Table 11·4. A major part of the ob-
Almost all of the CFC-11 and a significant portion of the
served ozone decrease is attributed to increased amounts of
other abundant CFCs (CFC-12 and CFC-113) are decom-
stratospheric chlorine (ClO) and resulting heterogeneous
posed by photolysis during transport from the troposphere to
chemical losses on polar stratospheric cloud particles and
the stratosphere (Kawa et al. 1992a, Woodbridge et al. 1995).
sulfate aerosols (WMO 1992, 1995). Many aspects of the
The photolysis products that most affect stratospheric chem-
observed changes in Arctic ozone are not well understood,
istry are chlorine (Cl) and chlorine oxide (ClO), which react
and the relative importance of additional processes, includ-
with ozone in a catalytic cycle that regenerates the chlorine
ing stratospheric cooling and dynamical changes, is an area
atom. Chlorine eventually forms stable reservoir species that
of active research. Complicating the search for long-term
are inactive toward ozone, such as hydrogen chloride and
trends are natural, nonlinear disturbances, such as the signi-
chlorine nitrate. In the presence of polar stratospheric clouds,
ficant decrease in ozone which occurred during the early
however, these reservoir species can decompose and augment
1990s following the injection of sulfate aerosols by the
the abundance of active chlorine in the polar stratosphere.
Mount Pinatubo volcanic eruption (Randel et al. 1995).
Current global concentrations of active stratospheric chlo-
Longer-term variations in other variables such as tempera-
rine are about 3.5 ppbv, substantially higher than the nat-
ture and aerosol surface area distribution may also have
ural background of 0.6 ppbv which arises mainly from the
contributed to the magnitude and timing of ozone losses in
stratospheric degradation of methyl chloride (WMO 1995).
the northern hemisphere (Solomon and Daniel 1996).
The importance of ClO lies in its ability to catalyze the
Because of the temperature dependence of heterogeneous
destruction of ozone. By a sequence of reactions involving
reaction rates, decreased temperature in the lower stratos-
ClO, BrO, and sunlight, the ozone concentration in the
phere may further accelerate chemical losses of ozone (e.g.,
polar stratosphere is reduced. These reactions are particu-
Herman and Larko 1994). Randel and Cobb (1994) sug-
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
741
Table 11·3. Satellite instruments for ozone measurements a.
Instrument
Platform
O3 measurement
Latitude range b
Time period
HALOE
UARS
O3 profile, 15-80 km (z = 2 km)
80°N to 80°S
1991 to present
LIMS
Nimbus 7
O3 profile, 10-65 km (z = 2.8 km)
84°N to 64°S
1978-1979
MLS
UARS
O3 profile, 15-50 km (z = 4 km)
80°N to 80°S
1991 to present
POAM II
SPOT-3
O3 profile, 10-50 km (z = 1 km)
55°N to 71°N
1993 to present
63°S to 88°S
SAGE I
AEM-2
O3 profile, 10-55 km (z = 1 km)
80°N to 80°S
1979-1981
SAGE II
ERBS
O3 profile, 10-65 km (z = 1 km)
80°N to 80°S
1984 to present
SBUV
Nimbus 7
O3 profile, 25-55 km (z = 8 km)
80°N to 80°S
1978-1987
SBUV/2
NOAA-11
O3 profile, 25-55 km (z = 8 km)
80°N to 80°S
1988 to present
NOAA-9 c
1985-1990
SME
SME
O3 profile, 45-65 km (z = 3.5 km)
85°N to 85°S
1982-1986
TOMS
Nimbus 7
Total ozone
90°N to 90°S
1978-1993
Meteor 3
1991 to present
GOES
ERS-2
Total ozone
90°N to 90°S
1995 to present
TOMS
ADEOS
Total ozone
90°N to 90°S
1996 to present
TOMS
Earth Probe
Total ozone
90°N to 90°S
1996 to present
a. Satellites for ozone monitoring have not always covered the polar regions. Since the discovery of the Antarctic ozone hole, satellites have been launched
to cover the polar regions with the added benefit of providing coverage for the Arctic. Nevertheless, the instruments usually require sunlight, thus pre-
venting full coverage of the Arctic ozone layer for the entire year.
b. The latitude ranges are, in general, not realized during all seasons. Many of the measurements are daylight measurements, thus cannot be obtained for
the highest northern latitudes during the local winter (Miller 1989).
c. The calibration system for the SBUV/2 instrument on the NOAA-9 satellite was unsuccessful. A third SBUV/2 instrument was on board the NOAA-13
satellite, which was launched in August 1993 but failed soon after launch.
gested that lower-than-normal temperatures measured by
Because of the combined influence of stratospheric tem-
the Microwave Sounding Unit at polar latitudes (65°to 90°N)
perature, dynamics, aerosols, and chemistry on stratospheric
during 1993 were due to radiative effects of decreased ozone,
ozone concentrations, linking ozone changes within the Arc-
as measured by Total Ozone Mapping System (TOMS) and
tic directly and exclusively to anthropogenic activity is diffi-
Solar Backscattering Ultraviolet (SBUV).
cult. Nonetheless, evidence exists that anthropogenic activity
Dynamical processes can result in concurrent, transport-re-
has had an impact on the observed ozone depletion. Ozone
lated changes in ozone and temperature in the lower strato-
depletion over the Former Soviet Union was measured using
sphere (e.g., Roldugin and Henriksen 1996, Finger et al. 1995).
re-evaluated filter-ozonometer data from 1973-1995 (Bojkov
There is evidence that the observed strong longitudinal depen-
et al. 1995b). Ozone depletions averaged 12% for winter
dence of total ozone and lower stratosphere temperature trends
and spring and 5% for summer. These depletions in ozone
in winter (e.g., Randel and Cobb 1994) are a consequence of
could be explained neither by natural ozone fluctuations nor
long-term changes in stratospheric dynamics, specifically in the
by instrumental errors. Although the LIMS (Limb Infrared
structures of quasi-stationary waves propagating up from the
Monitor of the Stratosphere) measurements were of short
troposphere (Hood and Zaff 1995). Long-term changes in
duration, they are particularly valuable since they were made
lower stratospheric circulation and ozone transport may also
before lower stratosphere ozone losses due to chlorine chem-
contribute significantly to zonal mean ozone trends.
istry were significant. Manney et al. (1994a) compared the
Measurements of the vertical profiles of ozone are valu-
evolution of ozone on the 465 K potential temperature sur-
able for interpreting the cause of observed ozone trends. For
face in the Arctic vortex derived from LIMS data during the
example, ozone in the Arctic vortex derived from Micro-
1978/79 winter with MLS observations in the winters of
wave Limb Sounder (MLS) observations showed no decrease
1991/92 and 1992/93. One of their conclusions was that the
in total column ozone during the winter of 1992/93 (Froi-
LIMS data should be used cautiously when interpreting that
devaux et al. 1994), yet MLS profile measurements showed
recent decreases in vortex-averaged ozone are due to chemi-
a decrease of about 20% in the lower stratosphere. Since the
cal rather than dynamical processes. The LIMS data showed
ozone in the Arctic polar mid-stratosphere was increasing at
a delayed increase in vortex ozone early in the 1978/79 win-
this time, it was concluded that the increase at the higher al-
ter, and a short decrease in January 1979; both of these ob-
titudes masked the decrease in the lower stratosphere in the
servations could be interpreted as evidence for chemical de-
column measurements (Manney et al. 1994a).
pletion, which would not have occurred at a significant level
Table 11·4. Ozone trends in the Arctic. A variety of studies examining ozone in the Arctic show consistent evidence for a decrease in mean ozone levels
for the Arctic. The variety of different instruments, platforms, and analyses all showing similar downward trends in ozone demonstrate a strong consen-
sus as to current changes in ozone.
Location
Instrument
Trend in % per decade
Time period
Reference
Western Siberia
Dobson
3.5±0.8
1973-1994
Bojkov et al. 1994
Eastern Siberia and the Far East
Dobson
3.2±0.8
1973-1994
Bojkov et al. 1994
Arctic
Dobson
7.5±3.8
1964-1994 (winter/spring)
Bojkov et al. 1995a
Arctic
Dobson
5.6±2
1964-1994
Bojkov et al. 1995a
50-65°N
Dobson
1.37±0.34
1964-1991
Reinsel et al. 1994
50-65°N
Dobson
1.54±0.42
1971-1991
Reinsel et al. 1994
50-65°N
Dobson
2.71±0.43
1978-1991
Reinsel et al. 1994
00-55°N
TOMS and SBUV
5.0
1979-1991
Rusch et al. 1994
00-60°N
SBUV
5 (lower stratosphere)
1978-1990
Hood and McCormack 1992
50-60°N
TOMS
3.96±1.15
1978-1991
Reinsel et al. 1994
50-60°N
TOMS
5.03±1.46
1978-1991 (winter)
Reinsel et al. 1994
00-65°N
TOMS
5.1±1.1 to 8.7±2.0
1978-1993
Herman and Larko 1994
00-60°N
Sage I/II
3.5
1979-1991
McCormick et al. 1992
63-90°N
TOMS/SBUV
10.7±1.8
1978-1997
Newman et al. 1997
50-60°N
TOMS
1.8 to 6.7
1978-1994
McPeters et al. 1996
60-70°N
TOMS
2.4 to 6.9
1978-1994
McPeters et al. 1996
70-80°N
TOMS
1.5 to 8.8
1978-1994
McPeters et al. 1996
742
AMAP Assessment Report
during the 1978/79 winter. After considering the behavior of
heat transport from lower latitudes.
long-lived tracers in order to separate chemical and dynami-
Two types of ozone anomalies have been observed in the
cal effects, Manney et al. (1994b) concluded that MLS
Arctic over the past decade: short term type 1, lasting a few
ozone measurements in February and March of 1993 indi-
days, and more long term type 2 lasting for several weeks
cated that Arctic ozone depletion by chlorine chemistry was
(Taalas et al. 1995, 1996, 1997). For both types, the losses
indeed occurring.
in total ozone have exceeded 35%. The location of ozone
The vertical distribution of ozone in and out of the Arctic
anomalies in relation to the location of the polar vortex and
vortex during the winters of 1993/94 and 1994/95 shows
the stratospheric temperatures provide information as to the
that ozone concentrations at the beginning of the winter in
possible cause of the anomalies. While these two categories
the lower stratosphere were higher inside than outside the
for describing ozone anomalies are useful, all ozone deple-
vortex. Subsequently, concentrations inside the vortex de-
tion events are not easily divided into dynamic or chemically
creased so that by the end of winter the mixing ratios inside
driven, nor inside or outside of the vortex.
were lower than outside. This behavior is consistent with
Finnish data from Sodankylä have been compared with
chemical depletion, but further knowledge of the relevant
the long-term (1935-1969) total ozone means from Tromsø,
dynamics is required before making a stronger statement
as recalculated by Bojkov et al. (1995a). Anomalies of 10%
(Randall et al. 1995). Evidence from MLS ozone measure-
and greater from those at Sodankylä were chosen for further
ments suggests chemical depletion of ozone in the lower stra-
analyses. The anomalies were sorted according to stratos-
tosphere inside the vortex during the winters of 1991/92,
pheric temperature observed at Sodankylä. Most of the ano-
1992/93, and 1993/94 although dynamical mechanisms were
malies observed in the European Arctic during recent years
not ruled out (Manney et al. 1995a). By comparing data
are connected to `warm' stratospheric temperatures. This
from ozonesondes and lidars over Thule, Greenland during
may mean low probability for the occurrence of Polar Stra-
the winters of 1991/92 through 1993/94, di Sarra et al.
tospheric Clouds (PSC's) in the airmass, which suggests a
(1995) concluded that dynamical perturbations caused a neg-
considerably different mechanism for ozone loss in the Arc-
ative correlation between ozone and aerosol concentrations,
tic compared with the Antarctic. For example, substantial
and masked possible chemical effects such as enhanced ozone
chemical ozone loss in the 1993/94 Arctic winter occurred
depletion on aerosol surfaces. Studies such as these highlight
mainly during an unusually cold ten-day period in late Feb-
the complementary nature of observational studies of the
ruary and early March (Manney et al. 1995c). According to
chemical behavior of long-lived trace gases and theoretical
a detailed study of inter-hemispheric differences using UARS
studies exploring the dynamical properties of the stratosphere.
data (Santee et al. 1995), although ClO is enhanced over the
Arctic as well as over the Antarctic, denitrification and sub-
sequent rapid ozone loss is inhibited in the Arctic due to the
11.3.5. Arctic ozone anomalies
generally higher temperatures. Future cooling of the Arctic
While the decadal trend of ozone in the Arctic is negative,
lower stratosphere could lead to more severe anomalous
there is inter-annual variability and, more importantly,
ozone losses in the northern spring.
short-term episodes of severe depletion in areas of a few
It is unclear whether ozone anomalies have an impact on
hundred kilometers in diameter. Data suggest that ozone
trends. Longitudinally averaged trends may obscure the im-
depletions as large as 20% may have occurred inside the
pact of these events and it is even possible that no change
northern polar vortex in the 1980s (Brune 1990, Profitt
will take place in the monthly or yearly mean ozone levels,
et al. 1990) and as much as 40% in the 1990s (SESAME
despite the occurrence of isolated events of severe ozone de-
1995). Recent studies indicate that both dynamics and
pletion. Nevertheless, the timing and severity of the ozone
chemistry play important roles in these anomalies. Dynam-
anomalies may have significant impacts on biological activity.
ically induced variations include those associated with the
These issues are addressed in sections 11.5.1.2 and 11.5.2.3.
Quasi-Biennial Oscillation (QBO) and the 11-year solar
cycle (WMO 1992, 1995). The QBO modulation at middle
11.3.5.1. Type 1 Arctic ozone anomaly
and high latitudes is most pronounced during the winter
spring season (e.g., Tung and Yang 1994, Hood and Mc-
Type 1 Arctic ozone anomalies are dynamically induced, gen-
Cormack 1992). Strong negative ozone anomalies at high
erally as a result of low ozone air masses transported north-
northern latitudes occur during the westerly phase of
ward from mid-latitudes. These anomalies usually occur
the equatorial QBO as observed in winter-spring of 1993
outside of the Arctic polar vortex and are generally short-
and 1995.
lived, lasting less than two weeks, and often less than a few
The 1995 winterspring negative ozone anomaly over
days. The complicated nature of these events is illustrated in
northern middle and high latitudes was particularly prom-
Figure 11·15, which shows the evolution of a type 1 ozone
inent and included a new record low minimum of 25% over
anomaly. The anomaly is formed by the intrusion of low-
Siberia and parts of the Arctic (Bojkov et al. 1995a). At the
ozone air from lower latitudes, which then becomes isolated
same time, the polar vortex was displaced over northern
inside the polar vortex, where chemical reactions cause a
Siberia and temperatures in the lower stratosphere were well
further reduction in the ozone concentrations.
below normal. The relative importance of dynamical trans-
port and chemical losses accelerated by the reduced temper-
Figure 11·15. Development of a type 1 ozone anomaly. The series of satel-
lite images show total column ozone for a period of days spanning 6-26
atures in producing this anomaly is being investigated. A
January 1996. The anomaly was primarily caused by the dynamic atmos-
comparison of northern winters since the 1991 launch of
pheric circulation, and then augumented by chemical reactions. January 6:
Upper Atmosphere Research Satellite (UARS) with those of
a `normal' Arctic image with typically higher ozone (green colours) nearer
earlier years indicates that the 1994/95 winter was marked
the pole and an assymetric distribution around the pole due to the unsta-
ble polar vortex. January 14-15: insurgence of lower-ozone air (orange
by an unusually early cold spell and a more isolated vortex
colours) from mid-latitudes coming northward over central Europe.
(Zurek et al. 1996). These characteristics would seem to be
January 17: the migrated low-ozone air is isolated by the polar vortex.
more conducive to ozone loss by heterogeneous chemistry
January 22: the ozone concentration within this isolated air mass (most
visible over Scandinavia) is lowered to approximately 200 Dobson units,
(Chipperfield et al. 1996). On the other hand, a more iso-
presumably due to chemical destruction. January 26: the dissolution of
lated vortex might also result in reduced eddy ozone and
this ozone event after a few days. (Source of data: SBUV-2 on Nimbus 14).
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
743
6 January
14 January
15 January
17 January
26 January
22 January
Dobson units
225 250 275 300 325 350 375 400 425 460 475
No data
744
AMAP Assessment Report
Altitude
Altitude
km
km
30
35
Ozone, 23 March 1995
Ozone, 27 January 1992
30
25
25
20
20
15
15
10
10
Ozone concentration in an ozone
Ozone concentration
5
hole at Gardermoen, Norway
5
at Sodankylä, Finland
Normal ozone concentration
Normal ozone concentration
0
0
0
5
10
15
mPa
0
5
10
15
20
mPa
Figure 11·16. Ozone soundings at Gardermoen, southern Norway, 27 Jan-
Figure 11·17. Ozone soundings at Sodankylä, Finland, 23 March 1995.
uary 1992. The green line denotes the partial pressure of ozone observed
The green line denotes the profile of partial pressure of ozone observed
during the (type 1) anomaly, when low-ozone air passed over the area.
during the (type 2) anomaly. The red line shows the monthly mean ozone
The red line indicates the 1989-91 January mean ozone profile at Sodan-
profile for March.
11£19d01
kylä, Finland.
Another example of a strong total ozone anomaly with a
minimum of 196 Dobson Units (DU) was observed moving
eastward over the European Arctic during the period 25-29
January 1992 (Taalas et al. 1995). The diameter of the ano-
maly was approximately 2000 km. The potential vorticity
analyses for the 475 K and 380 K surfaces indicate an air
mass with low ozone values, and a 3-dimensional trajectory
analysis for the lower stratosphere indicated a subtropical
origin for the airmass before reaching Gardermoen in south-
ern Norway. An ozone sounding performed while the anoma-
ly area was passing over Gardermoen (Figure 11·16), showed
that the primary ozone loss was observed in the lower stra-
tosphere below the ozone maximum and well below the lev-
els where low temperatures are typically observed.
Similar features may be found to have been behind the
other strong deviations observed in the European Arctic
during early 1992 (Taalas and Kyrö 1994). These findings
demonstrate the importance of large-scale circulation as a
modifier of the global ozone distribution in contrast to the
dominant chemical ozone loss observed in Antarctica.
11.3.5.2. Type 2 Arctic ozone anomaly
-27 -24 -21
-18 -15 -12
-9
-6
-3
0
3
6 %
Type 2 Arctic ozone anomalies are primarily chemically in-
duced and are generally observed in connection with a strong
polar vortex and the presence of Polar Stratospheric Clouds
Figure 11·18. An example of a type 2 ozone anomaly, showing levels of
(PSCs). In 1995 a cold polar vortex was observed over the
ozone depletion relative to the long-term mean.
European Arctic until late March. Both PSC's and ClO were
observed inside the Arctic polar vortex and severe ozone de-
pletion was measured. The resultant ozone loss was recorded
11.4. UV radiation
with a variety of techniques including an ozone sounding
made inside the polar vortex (Figure 11·17). Analyses of
The most direct effect of changes in ozone is a change in UV
temperature and potential vorticity indicate that the ozone
radiation reaching the biosphere. Despite the low sun angle
anomaly was located inside the polar vortex at temperatures
in the Arctic, UV radiation has always been an environmental
below 195 K (Taalas et al. 1997). The ozone loss was strong-
threat, even before ozone depletion. Snow blindness (photo-
est in the cold airmass between 17 and 21 km altitude, with
keratitis), which is directly caused by UV radiation, is an en-
maximum negative ozone deviation exceeding 60% from the
vironmental risk which indigenous Arctic populations have
1989-1991 March mean partial pressure of ozone in the
always needed to protect themselves against. Recent changes
same altitude range. Figure 11·18 shows an example of a
in the Arctic ozone layer have heightened concern about the
type 2 ozone anomaly when record low ozone levels of 30-
effects of UV radiation on indigenous peoples and on the en-
35% below the long-term mean were recorded over Siberia
vironment in which they live (Wulf 1994). Direct and diffuse
from February-March of 1995 (Bojkov et al. 1995b).
radiation both affect biological systems, and the amount of
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
745
UV and visible radiation at the earth's surface is highly vari-
Albedo
Transmittance
able due to many factors. The amount of ozone, and hence
1.0
UV, can vary greatly from day to day, and cloud cover, in-
cluding Arctic haze, can cause variations on even shorter
10-1
time scales. In the Arctic, decreases in ozone in the winter
0.8
result in increased UV during a time when many plants are
protected by snow and the sun is low on the horizon; spring-
0.6
time decreases in ozone, however, are likely to result in UV
10-2
increases during critical phases of biological productivity.
Recently observed ozone anomalies have occurred in the
0.4
spring when some biological organisms are most sensitive.
UV radiation is composed of all radiation between 100
10-3
and 400 nm. It is further broken down into sub-categories:
0.2
UV-A 315-400 nm
UV-B 280-315 nm
0.0
UV-C 100-280 nm
10-4
300
320
340
360
380
400 300
320
340
360
380
400
Visible radiation, or Photosynthetically Active Radiation
Wavelength (nm)
Wavelength (nm)
(PAR), is above 400 nm.
Figure 11·19. Ultraviolet albedo and transmittance values
Variations in stratospheric ozone modify the amount of
A
B
for A) thin (0.3 m) bare sea; B) cold 1.6 m thick ice with a
solar UV radiation available for absorption in the atmos-
C
0.1 m deep snow cover in April; C) bare 1.7 m thick ice in
phere and at the surface, and lead to changes in a) atmos-
May; and, D) ponded ice with 0.1 m of water over 1.5 m
D
pheric composition through altered photochemistry, b) at-
thick ice. A was measured in the laboratory and B, C and
D were measured in shorefast first-year ice near Barrow,
mospheric circulation through changes in warming/cooling
Alaska (Perovich 1993).
rates, and c) terrestrial and aquatic ecosystems through
modulations in biologically effective UV radiation reaching
The contribution from the surface to the downward irra-
the biosphere (IASC 1995). The response of the atmos-
diance (due to multiple reflections between the atmosphere
phere-hydrosphere-biosphere system to such photochemical
and the surface) depends on the spherical albedo, which is
and radiative changes is not well understood.
the same as the flux reflectance for uniform illumination of
Surface albedo, clouds, total column ozone, vertical dis-
the atmosphere from below (Stamnes 1982). For a cloudy
tributions of ozone, pollutants, and Arctic haze can affect
atmosphere, spherical albedo is large and gives rise to a non-
the transmission of UV through the Arctic atmosphere (Tsay
linear behavior of the downward irradiance as a function of
and Stamnes 1992). The effects are not always apparent
surface albedo (Kylling et al. 1995). This yields a much
because the diffuse and direct components of the radiation
more pronounced dependence on surface albedo for cloudy
field can be differentially altered. Henriksen et al.(1989)
than for clear atmospheric conditions.
demonstrated clearly that diffuse radiation comprises the
majority of the total UV radiation at the surface in the sum-
11.4.1. Measurements
mertime Arctic. For low solar elevations, stratospheric aero-
sols may lead to an increase in UV dose rate, while Arctic
Ground-based measurements of UV radiation are the best
haze results in a decrease. A redistribution of ozone from the
method available for assessing UV levels. Unfortunately,
stratosphere to the troposphere also tends to decrease UV
these measurements are difficult, expensive, and cannot be
exposure, in agreement with previous findings of Brühl and
made throughout the Arctic. A variety of UV measurements
Crutzen (1989) and Frederick et al. (1989), except for low
have been taken in the Arctic for many years (e.g., Wester
solar elevations when an increase may instead occur (for a
1996, Hisdal 1986, Stamnes et al. 1988). Solar UV measure-
physical explanation, see Tsitas and Yung 1996).
ments have been the subject of several reviews (cf. Blum-
UV and visible irradiance at the surface depend strongly
thaler 1993), but in the early 1990s, few national programs
on surface albedo for clear, aerosol-loaded atmospheres as
for monitoring UV irradiance included Arctic installations.
well as cloudy atmospheres. Snow is one of the few natural
Several types of instruments are presently used to mea-
materials whose reflectance (local albedo) is high enough to
sure UV in the Arctic. Spectrometers and photometers have
substantially increase the UV radiation reaching the ground.
been used in the Arctic since 1927 (Dobson 1968b) to make
For fresh snow the UV reflectance may be as high as 94%
measurements of the direct solar beam, or the zenith sky.
(Blumthaler and Ambach 1988, Grenfell and Warren 1994).
These contrast with radiometric UV measurements where
In other studies, albedos for snow range from 0.76 (Feister
the intensity of UV radiation is measured in Watt/m2 or
and Grewe 1995) to 0.97 at 300 nm for the South Pole
Watt/m2/nm or in some other related measure such as a bio-
(Grenfell and Warren 1994). This is considerably higher
logical dose. UV measurements can be further divided into
than the albedo for open water and vegetation (McKenzie
narrow-band that are spectrally resolved (e.g., by spectrora-
and Kotkamp 1996).
diometers) and broad-band meters that present a single mea-
Under cloudy conditions, multiple reflections may occur
sure, such as `UV-B' or `erythemal dosage'. Spectroradio-
between the snow covered surface and the clouds, increasing
meters have the advantage of being able to compute a wide
UV considerably from that which would have occurred if
variety of single measures, allowing separation of the effects
the surface were not snow covered. Perovich (1993) made
of changes in cloud cover or atmospheric clarity and total
laboratory and field observations of the reflection of ultravi-
column ozone (Stamnes et al. 1991), while single measure
olet radiation by young and first-year sea ice (Figure 11·19).
devices do not.
Ultraviolet albedos for cold, bare, first-year sea ice are be-
There is little agreement in the international community
tween 40 and 60%. The presence of even a thin snow cover
on the kind of instrument to use, nor is there a single stan-
was found to significantly increase the ultraviolet albedo
dardized spectroradiometer or even a standardized operating
and greatly reduce the transmission.
protocol or calibration method. Several national and inter-
746
AMAP Assessment Report
Table 11·5. UV monitoring sites inside the Arctic Circle. Most UV monitoring efforts in the Arctic were started within the last decade, making long-term
assessments of UV difficult. The lack of sites in the Russian Arctic limits our ability to monitor changes in Arctic UV levels today.
Location
Coordinates
Operator
Instrument
Established
Tromsø, Norway
70°N, 019°E
University of Tromsø
JY32D, GUV-511
1987
Ny-Ålesund, Norway
79°N, 012°E
NPI
GUV-511, SL500, SL501
1990
Longyearbyen, Norway
78°N, 016°E
Univ. Tromsø
JY H32D
1991
Barrow, Alaska
71°N, 156°W
NSF, (Biospherical)
SUV-100
1990
Resolute, Canada
75°N, 095°W
AES Canada
Brewer
1992
Alert, Canada
82°N, 062°W
AES Canada
Brewer
1992
Eureka, Canada
80°N, 086°W
AES Canada
Brewer
1993
Thule, Greenland
76°N, 069°W
DMI
DMI (.22 m double)
1994
Søndrestrøm, Greenland
67°N, 051°W
DMI
Brewer MkII
1990
Abisko, Sweden
68°N, 019°E
Univ. Lund
SL501
Kiruna, Sweden
67°N, 021°E
SMHI
SL500
1989
Sodankylä, Finland
67°N, 027°E
FMI
Brewer MkII
1989
Varrio, Finland
67°N, 030°E
University of Helsinki
SL501A
1995
national UV instrument intercomparisons have been held to
ently to the various components of UV-A and UV-B radia-
address problems with measuring UV (Koskela 1994, McKen-
tion, it is difficult to summarize UV radiation for biological
zie et al. 1993, Seckmeyer et al. 1994, Gardiner and Kirsch
use. Furthermore, standard methods of monitoring UV are
1995). There are several national UV monitoring networks
inappropriate for research on UV effects in Arctic conditions.
that include Arctic sites (see Table 11·5) (Kerr and Wardle
1993, Johnsen 1996). The Nordic countries, Sweden, Finland,
11.4.3.1. Spectral considerations
Norway, Denmark, and Iceland, are organized into the Nor-
dic Ozone Group; each country operates its own UV monitor-
The total amount of UV radiation does not adequately de-
ing network with strong cooperation between the scientists.
scribe the amount of harmful UV radiation because of the
differing efficacies of photons within the UV spectrum: the
shorter wavelength photons are several orders of magnitude
11.4.2. Modeling
more damaging than the longer wavelengths (UNEP 1994,
Models of UV radiation, using satellite data to estimate the
SCOPE 1993). The relative harmfulness of the various re-
relevant components of the atmosphere, provide estimates of
gions within UV may be summarized by a Biological Weight-
UV in regions where UV monitoring does not exist. How-
ing Function (BWF) which is unique to the process being
ever, the complexity of the atmospheric and environmental
studied. Biologically relevant UV is determined by weighting
r
conditions makes estimates difficult in the Arctic, particu-
the spectral radiation by its biological effectiveness.
larly in partly cloudy situations. Considerable progress has
Biologically effective UV can be summarized in terms of
been made in understanding the relationship between atmos-
its response to changes in ozone. At mid-latitudes, a change
pheric conditions and the UV irradiance incident on the
of one percent in ozone may result in a change of between
ground for mid-latitudes. But, the limitations in predicting
one and three percent in biologically weighted UV, depend-
or modeling ground level UV are greatest in polar regions
ing on the action spectra being considered. The percent in-
where a combination of uncertainty in albedo due to chang-
crease in UV dose rate per percent decrease in ozone amount
ing snow or ice conditions, frequent cloud cover, and the in-
(radiation amplification factor) is largest (and tends to increase
creased uncertainty in radiative transfer models at low solar
with solar zenith angle) for biological responses which are
angles greatly complicate the estimation of surface UV using
heavily weighted toward UV-B radiation (e.g. plant response),
satellites. The use of ground-based UV measurements is cru-
while biological effects with significant response to UV-A ra-
cial to the development of reliable algorithms for using satel-
diation (e.g. erythema) will have a smaller amplification fac-
lite information to estimate UV levels in the Arctic.
tor that decreases with increasing solar zenith angle. Large
One of the least understood components of this complex
changes in ozone result in non-linear changes in UV (Booth
system is the radiative effects of particulate clouds, as well
and Madronich 1994). These relationships were derived by
as the environmental conditions leading to their formation
examining the relationship between ozone and UV at mid-
and dissipation. The effects of molecular multiple scattering,
latitudes; further work needs to be done to determine the
solar elevation, surface albedo, and cloud properties (such
relevance of these relationships in polar regions.
as optical depth, altitude, and cloud fraction) on ozone ab-
sorption have been studied using radiative transfer models
11.4.3.2. Geometrical considerations
of varying degrees of sophistication (Shettle and Green
1974, Luther and Gelinas 1976, Spinhirne and Green 1978,
To reach biological receptors in the Arctic, UV radiation
Nicolet et al. 1982, Thompson 1984, Madronich 1987,
must often travel through snow, water, or ice. Even biologi-
Frederick and Lubin 1988, Frederick and Snell 1990, Smith
cal receptors which are on open land require special consid-
et al. 1992, Stamnes et al. 1990, 1992).
erations in parameterizing UV radiation. Traditionally, the
exposure of human populations and ecosystems to solar UV
radiation is commonly described using measurements of the
11.4.3. Biologically relevant UV
biologically weighted irradiance hitting horizontal surfaces
The present understanding of the relationship between the
which is at best an approximation because UV hits biologi-
UV climatology and biological exposure in snow covered
cal organisms at many different angles. New methods of pa-
regions is inadequate to fully assess the impacts of ozone
rameterizing UV become particularly important when trying
depletion on the Arctic. Three factors make assessing bio-
to assess UV effects in the Arctic. Previous methods have
logically relevant UV difficult in the Arctic: a) the high sur-
proven inadequate and vastly under-estimate the impact of
face albedo; b) extremely low sun angle; and c) many of the
UV on Arctic ecosystems and human inhabitants because of
biological receptors in the Arctic are under snow, water, or
the increased fraction of UV radiation that is scattered rela-
ice. Because different biological processes respond differ-
tive to direct UV radiation.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
747
11.4.4. UV on land
Daily dose
kJ/m2 (CIE)
Measurement of UV striking a horizontal surface is not al-
4 000
ways appropriate to describe UV irradiance in the Arctic.
For many biological systems, particularly in the Arctic, the
3 000
UV reaching a vertical surface which is rotated over 360° to
give the average irradiance reaching a vertical surface may
give a more relevant measure of biologically important UV.
2 000
The difference between UV reaching a horizontal and a ver-
tical surface can be particularly critical in the Arctic when
snow cover is present. In environments of high UV reflectiv-
1 000
ity and especially when the terrain is open and not covered
by trees, buildings, etc., UV exposure to the face and eyes is
strongly affected by reflected UV. Under these conditions,
0
measurements of exposure on vertical surfaces give good
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
estimates of the exposure received by different parts of the
UV on a horizontal surface with normal ozone
face and eyes.
UV on a vertical surface with normal ozone
Theoretical models are available for measuring UV on a
UV on a vertical surface with normal ozone and no snow
vertical surface (Dahlback and Moan 1990, Hay and Davies
UV on a vertical surface computed from measured values
1978, Bird and Riordan 1986, Schauburger 1992), and have
Figure 11·20. Theoretical clear-day UV dose to horizontal and vertical
been used to estimate the effect of ozone depletions on skin
surfaces, for Arctic Finland. The amount of energy from UV radiation
cancer (Moan and Dahlback 1993) and the increase of UV
reaching a horizontal surface peaks around midsummer, while that reach-
due to the reflection from snow (Jokela et al. 1993, Jokela et
ing a vertical surface peaks in early spring, in part due to efficient reflec-
tion by snow. The irregular line shows the results obtained by using mea-
al. 1995). Sliney (1986, 1994) has studied the different envi-
sured values for total ozone. The smooth lines were calculated with the
ronmental and anatomical features contributing to UV ex-
mean (climatological) total ozone. The dashed line depicts the mean verti-
posure of the eye. The results from these studies may be ap-
cal exposure with summer albedo (0.04). The theoretical curves are realis-
tic only for clear skies with fresh snow.
plicable to UV effects on other biological systems. Simple
algorithms have been proposed (Hay and Davies 1978, Bird
dose reaching a horizontal surface than on the UV dose reach-
and Riordan 1986) and tested (Jokela et al. 1993) for con-
ing a vertical surface. In southern Finland, the effect of ground
verting irradiance on a horizontal surface, as is typically
reflectivity on both horizontal and vertical exposure is rela-
measured, to irradiance on a vertical surface for a given
tively small because the snow melts before UV increases to
albedo. These algorithms are particularly useful in the high-
significant levels. Also, the terrain is covered by trees and
albedo, low-sun-angle conditions often found in the Arctic.
buildings, which effectively reduce reflectivity. The snow
While UV reaching a vertical surface may give a more
albedo effectively smooths out geographical differences in
accurate dose than UV on a horizontal surface for some bio-
the dose of UV: the computed dose on a horizontal surface is
logical systems in the Arctic, measurements of biological ex-
about 29% higher in Helsinki than in Saariselkä, while the
posure are complicated further by natural protective mech-
difference is only 12% for UV on a vertical surface.
anisms. Snow has an even greater effect on radiation reach-
UV has been thought to be considerably less in the Arctic
ing the eyes than that reaching the face due to the anatomy
than at mid-latitudes. However, when one examines the dif-
of the head and eyes. The viewing angle of the eyes, which
ference in UV to a vertical surface as a proxy for UV reach-
varies according to the amount of squinting, is considerably
ing a human face or eyes, as a function of latitude, the dif-
less than 30 degrees vertical above the horizon and less than
ference between mid-latitudes and the Arctic is not as great
180 degrees in azimuth, and the eyes normally look toward
as one might expect. Figure 11·21 shows a comparison of
the ground or horizon (Sliney 1986, 1994). In bright sun-
the computed annual UV doses to vertical and horizontal
light over snow, the squinting of the lids mimics Inuit slit
goggles and allows only a narrow vertical field of view of a
UV dose
kJ/m2 (CIE)
few degrees. This form of protection may be more effective
2 500
than many modern types of sunglasses which allow consid-
erable scattered light into the eye from the side.
Because ocular damage by UV radiation has always been
2 000
horizontal surface
a health hazard in the Arctic, ozone depletion is likely to
raise the importance of UV as an environmental health con-
cern for the Arctic populations. Figure 11·20 illustrates the
1 500
effect of snow on erythemally effective UV received by hori-
zontal and vertical surfaces in northern Finland (Saariselkä,
1 000
68.4°N, 27.5°E) (Taalas et al. 1996). The irregularly plotted
vertical surface
line shows the results computed by using the actual total
ozone measured by the nearby Meteorological Observatory
500
in Sodankylä (67.4°N, 26.6°E). For the winter, a reflectivity
of 0.8 was adopted, which decreased linearly to the summer
value of 0.04 during the period of 25 days before the end of
0
the snow season (16 May). In the autumn the change was
0
10
20
30
40
50
60
70
assumed to be abrupt (24 October).
Latitude °N
In Saariselkä, snow albedo increases total UV exposure to
Figure 11·21. Average annual UV dose falling on vertical and horizontal
the face in winter and early spring by a factor greater than
surfaces as a function of latitude. The solid lines represent the situation
for the normal UV level with undisturbed ozone (prior to 1978). The
two. Exposure to these surfaces in April is equal to mid-
dashed lines are for the UV level following the maximum estimated global
summer exposure. Snow has a much smaller effect on UV
ozone depletion (in the year 2000).
748
AMAP Assessment Report
surfaces as a function of latitude. Additionally, the estimated
The maximum penetration of UV-B is found in oceanic
effect of global ozone depletion is shown (Taalas et al. 1996).
waters, while in coastal seawater the penetration is less due
Annual doses were corrected for the effects of clouds (Fred-
to a larger amount of Dissolved Organic Matter (DOM), es-
erick and Lubin 1988) and reflection from the snow at 60°N
pecially humic substances (Smith and Baker 1979). For the
and at 70°N. The latitudinal difference of the ratio of verti-
estuarine areas of the Arctic Ocean this is of major impor-
cal to horizontal dose is 0.35 at the equator and increases to
tance (Höjerslev and Aas 1991). In the waters off Svalbard
0.5 at high latitudes. This is mainly due to the relative in-
and western Greenland, diffuse attenuation coefficients rep-
crease of diffuse radiation from the sky and ground com-
resenting 10% radiation levels at 310 nm (Kd( 310)) were
pared with the direct radiation from the sun.
shown to be around 0.2, or a little more than 10 m, while in
The relative increase of the UV dose on a vertical surface
the North Sea the corresponding irradiation levels were at a
at high latitudes may have some influence on the relation-
depth of around 5 m and in Hardangerfjord, Norway levels
ship between the ozone depletion and the incidence of skin
were 1-2 m (calculated from Højerslev and Aas 1991).
cancers at different latitudes. Atmospheric, epidemiological
Theoretical estimates indicate that the presence of a sea
and animal studies show that the relative incidence of a skin
ice cover causes a significant reduction in the amount of UV
carcinoma increases exponentially:
transmitted and that UV-B radiation is attenuated more than
UV-A radiation or visible light. Even a modest snow cover
I1 / I2 = (D1/ D2)
BAF = (O3 / O )
RAF
BAF
1
32
( 0.15 m) reduces UV levels by nearly two orders of magni-
where I1 / I2 is the relative cancer incidence, D1/ D22 is the
tude (Perovich 1993). For young, thin sea ice UV transmit-
relative annual UV dose, O3 / O3 is the relative total
tance is large, roughly 20%, while for cold first year ice
1
2
ozone. Index 1 refers to the depleted and index 2 to unde-
transmittances are less than 2%. Extinction coefficients for
pleted conditions. BAF is the Biological Amplification Fac-
cold bare ice are between 2.5 and 3 per meter, in the range
tor and RAF is the Radiation Amplification Factor. When
of visible values observed for the interior of white ice and
the ozone depletion is below 10%, the amplification factors
the surface scattering layer of white ice (Grenfell and May-
are approximately the factors by which the percentage
kut 1977). In all cases, a larger portion of PAR is transmit-
change of the UV dose or ozone depletion must be multi-
ted than of the UV radiation. Wavelength-integrated extinc-
plied in order to obtain the percentage change in the cancer
tion coefficients for PAR are smaller than UV values.
incidence or UV dose, respectively. For Squamous Cell Can-
Models for solar radiative transfer through the coupled
cer (SCC) the current estimate for the BAF is BAF = 2.5 ± 0.7
atmosphere-snow/ice-ocean system have also been developed
(de Gruijl and van der Leun 1993). The erythemally effec-
(Jin et al. 1994a, 1994b, Zeng et al. 1993). However, data
tive UV radiation RAF decreases from approximately 1.2
on optical properties for snow, ice, and water in the UV are
to 1 from the equator to high latitudes. The BAFs have
scarce (see Trodahl and Buckley 1990) and few spectral irra-
been derived from the measured erythemal horizontal UV
diance measurements exist for testing of such models. Simul-
at different latitudes.
taneous spectral measurements of Arctic surface (snow and
Estimates of vertical BAF can be made by making as-
ice) and underwater UV optical properties, as well as UV ir-
sumptions about the angular distribution of radiation and
radiance and radiance measurements, are needed. Progress
applying a conversion factor derived from the calculations
awaits comprehensive experiments executed in the Arctic
of annual doses on both horizontal and vertical surfaces.
environment.
This conversion results in the increase of the BAF for the
Recently there has been growing concern about the im-
SCC from 2.5 to 3.2. It is interesting that the increased
pact of enhanced UV levels on ice biota in the Arctic as well.
BAF is closer to the murine BAF, which varies from 3.2
Diatom mats cover the undersurface of the ice over vast ex-
to 4.4 (de Gruijl and van der Leun 1993). The increase of
panses and form the basis of a food chain that extends from
the BAF based on the UV reaching a vertical surface is in
copepods and amphipods to cod, seals, and polar bears.
qualitative agreement with the results of Moan and Dahl-
Determining how much enhanced UV radiation at the sur-
back (1993), which examined the dependence of the ampli-
face reaches biological organisms living in and under the ice
fication factors from the receiving surface for the Norwe-
cover is difficult. This problem is complicated by the tempo-
gian population. They found that the RAF does not signifi-
ral and spatial variability in the physical and therefore opti-
cantly depend on the exposure geometry, but the total am-
cal properties of sea ice.
plification factor increases slightly from the exposure to
Penetration of UV in lakes and ponds varies greatly as
horizontal and vertical surfaces. Since the total amplifica-
a function of amount of dissolved organic matter; ice and
tion factor is the product of RAF and BAF, the latter must
snow cover also absorb UV-B for much of the year. Hessen
increase. Although the irradiation on a vertical surface de-
(1996) found 10% attenuation at 10 m for 310 nm in
scribes better the actual UV exposure than the horizontal,
alpine, subarctic lakes, while Arctic ponds that are slightly
it is still a very crude approximation of the complex expo-
more influenced by Dissolved Organic Carbon (DOC)
sure patterns.
have a 10% attenuation at a depth of 2-4 m for 310 nm.
A number of these lakes have maximum depths of less than
2 m. For Arctic lakes of Alaska, more influenced by humic
11.4.5. UV penetration in aquatic systems
compounds, Morris et al. (1995) also recorded low attenu-
The penetration of radiation in the PAR and UV regions
ation depths relative to high UV-B transparency in clear
in ocean and lake water depends on dissolved substances
alpine lakes.
and particles that attenuate light. Natural levels of UV-B
There is a limited number of underwater measurements
radiation are known to penetrate to ecologically signifi-
from Arctic and subarctic sites (Scully and Lean 1994, Hes-
cant depths in many bodies of water (cf. Smith et al. 1992,
sen 1993, 1996). In general, high latitude and high altitude
Scully and Lean 1994, Morris et al. 1995, Hessen 1996).
localities are low in DOC, implying low absorbance of UV-
Increases in UV-B radiation due to ozone depletion alter
B. Some alpine lakes are extremely UV transparent (Hessen
the spectral balance of UV-A, UV-B, and PAR and increase
1993, Schindler et al. 1997), while High Arctic localities at
the exposure of aquatic ecosystems to UV radiation (Smith
80°N span from extremely clear lakes to shallow ponds
et al. 1992).
slightly influenced by colored organic matter (Hessen 1996).
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
749
11.5. Effects of climate change
Many Arctic plant species are currently stressed by the
and UV radiation on the biosphere
harsh environment. Vegetation is subject to periodically fro-
zen soil, strong winds and ice crystal abrasion, short grow-
Climate change will affect biological processes and physical
ing seasons, and extreme temperature variations. Microbial
properties of the oceans and land, directly impacting the lives
decomposer activity is limited by cold, shallow soils overly-
of humans living in Arctic regions. The most obvious effects
ing permafrost so that few nutrients are available for plants.
of warming in the Arctic will most likely involve changes to
Soils are often either dry as in the polar deserts, or water-
the cryosphere (glaciers, permafrost, sea ice cover, and snow),
logged and anaerobic as in mires and polygonal sedge mead-
with consequent changes in biotic and biogeochemical pro-
ows; much of the year they are frozen. Changes in air tem-
cesses. Accurate predictions of change are complicated by
perature will warm the soil and will induce changes in the
complex interactions: on land between permafrost, the feed-
depth and moisture of the active layer where hydrologic,
back effects of soil changes on vegetation, and alterations in
geomorphic, chemical, and biological processes occur that
snow cover and precipitation; in the atmosphere between
profoundly affect ecosystems at the landscape level (Rey-
trace gas amounts, changes in ozone and atmospheric pollu-
nolds and Tenhunen 1996). In many systems, warming may
tants, and seasonal temperature and light regimes; and in the
increase soil biological processes of trace gas emission, de-
oceans between the sea ice albedo feedback, and changes in
composition of soil organic matter, and nutrient availability
sea ice extent and thermohaline circulation.
to plants but the resulting increase in leaf area index may
Temperature and precipitation are not the only environ-
reduce the penetration of solar radiation to the soil thereby
mental variables that are changing and the balance between
negating longer term soil warming or even resulting in soil
opposing responses to different environmental factors is not
cooling (Callaghan and Jonasson 1995). Increased soil mois-
clear yet. Increases in CO2 and UV radiation have the poten-
ture content in already wet soils may reduce the rates of
tial to change the chemical quality of plant tissues which
these processes through a shift in the balance of aerobic and
might reduce microbial decomposition rates by as much as
anaerobic conditions.
10% (Couteaux et al. 1991, Gehrke et al. 1995) and slow
Harsh Arctic conditions have acted as a filter to biodiver-
the release of carbon to the atmosphere. Increased UV cou-
sity, which is further constrained by the relative youth of
pled with climatic warming and acidification may increase
most tundra ecosystems. While biodiversity is low at the
the rate at which DOM is cycled in fresh water and increase
species level (Chapin and Körner 1995), populations are
the CO2 flux to the atmosphere (Schindler et al. 1997). Even
often large and geographical distributions extensive which
subtle changes in plant community distribution may have ef-
should mitigate against losses in biodiversity due to climate
fects on canopy roughness and the turbulent transfer of en-
changes. Arctic species have successfully survived changes in
ergy and water between vegetation and atmosphere. Effects
the past, such as climatic warming in medieval times, the re-
of climate change and UV are often counterintuitive and
covery from the Little Ice Age over the past 150 years, and
long term in situ studies are needed.
considerable variability in temperature between years in the
The Mackenzie Basin Impact Study (MBIS), which con-
present period (Havström et al. 1995).
sisted of 30 research activities and consultations with stake-
holders, represents one of the first attempts at an integrated
11.5.1.1.1. Vegetation
assessment of the impact of climate change on a region and
its inhabitants (Cohen 1996, 1997). Climate warming sce-
Plant communities
narios of 4-5ºC were obtained from three GCMs and a com-
Within the Arctic, the variation in vegetation ranges from
posite analogue based on paleoecological data. Results from
closed, relatively productive communities of the subarctic
two studies from the ecosystem component on boreal peat-
which support a diversity of herbivores, to sparse, unpro-
lands are provided in Nicholson and Gignac (1995) and
ductive vegetation of the High Arctic. This geographical
Nicholson et al. (1996).
variation in structure of plant communities and environ-
ments within the Arctic will result in different responses to
future climatic changes by different plant community types.
11.5.1. Terrestrial ecosystems
Although Arctic organisms can survive current harsh envi-
11.5.1.1. Climate change effects on terrestrial ecosystems
ronments, many can also tolerate higher temperatures ex-
The impacts of climate change on Arctic terrestrial ecosys-
pected to occur following climatic warming.
tems are complex and difficult to predict because of the
Plants exhibiting traits of slow growth, compact forms,
many interactions which exist within ecosystems and be-
and parsimonious nutrient use are predisposed to tolerate
tween many concurrently changing environmental variables
Arctic conditions but are also sensitive to competition from
(Chapin et al. 1992, Callaghan and Jonasson 1995). Primary
opportunistic, aggressive species from farther south. In a
production can be affected by higher temperatures, atmos-
warmer Arctic, the competition from more responsive spe-
pheric CO2 concentrations, and UV-B radiation; impacts
cies would probably threaten Arctic flora more than the en-
from such changes are uncertain and depend on the re-
vironment per se because many Arctic plants are sensitive to
sponses of soil microbial decomposer activity to changes in
shade and other competitive mechanisms (Callaghan and
soil temperature, moisture, and plant litter quality. Increases
Jonasson 1995). However, Arctic latitudes are broad and the
in atmospheric CO2 are expected to increase plant produc-
migrations of plants from southern latitudes will occur more
tion, increase translocation of carbon to below ground, re-
slowly than temperature changes. For example, a warming
duce nitrogen and increase lignin and tannin concentrations
of 2°C could result in a 4-5° latitude northward shift of the
in plant litters. Some of these changes are closely tied to UV-
climatic zone associated with the taiga of Eurasia (Velichko
B increases. Thawing permafrost can disturb the soil, which
et al. 1990), i.e., a shift of 400-500 km by the year 2020. If
would warm and further disturb vegetation, resulting in a
the taiga forests could migrate at this rate, tundra would be
change in species composition. A change in species composi-
totally displaced from the Eurasian mainland. However, ex-
tion due to competition effects from less sensitive local spe-
pected tree migration rates of 10-1000 meters per year are
cies and from intruding southerly species is also expected
insufficient to accomplish this. The disparity between rates
(Chapin et al. 1992, Körner 1994).
of predicted climate change and tree migration will result in
750
AMAP Assessment Report
some tundra areas experiencing supra-optimal thermal
climatic warming and increased precipitation on soil mois-
regimes which could adversely affect plant carbon balance
ture are hard to predict and may be site or regionally spe-
and survival.
cific. Increased temperatures may, however, desiccate moist
At a much smaller scale, those genotypes, or ecotypes,
soils and hence cause water stress to plants. Although little
within individual species which are more responsive to
research has been conducted on Arctic species, an increase in
change may out-compete those best adapted to the harshest
CO2 may also affect tundra ecosystems via plant water rela-
environments. Different ecotypes of the same species can
tions because, in general, water use efficiency increases with
grow close to each other but have different distributions;
enhanced atmospheric CO2 (Oberbauer and Dawson 1992).
some, for example, prefer sheltered, moist depressions, while
Increased efficiency might offset soil drying and allow spe-
others prefer more exposed sites. (Crawford et al. 1995)
cies to colonize marginal or barren areas of the High Arctic
Again however, slow rates of spread, i.e. small scale migra-
which would change the albedo and thus affect the energy
tion, will limit change. Plants of the harshest Arctic environ-
balance (Lashof 1989). Plant communities along rivers and
ments, sparsely located in a landscape, growing at 2 mm per
streams may be negatively affected by climate change. De-
year (Molau 1996), may take centuries to replace a neigh-
creased river and streamflow affects riparian ecosystems and
boring genotype.
the animals that inhabit them. A decrease in flooding and
subsequent drying of deltaic ecosystems will alter plant com-
Nutrient availability
position and reduce migratory bird habitat.
In many tundra ecosystems the response of plants to climate
changes will be influenced by the availability of nutrients, in-
11.5.1.1.2. Invertebrates
cluding those released by decomposition of organic matter
and mineralization from parent materials. Thus it is possible
One of the likely effects of climate change accompanying en-
that the growth potential of plants may not be realized be-
hanced temperature is a change in the pattern of outbreaks
cause of limitations in nutrient availability if the supply of
of pests and pathogens. The species involved may be indi-
nutrients from soil is less than or asynchronous with de-
genous but currently benign, or they may be immigrants
mand. The available evidence indicates that nitrogen and
from the lower latitudes.
phosphorus mineralization will increase in mesic more than
Invertebrates with relatively short generation times may
in dry tundra. Also, the increased depth of the active layer in
show great population dynamic responses to increased tem-
organic soils will tend to allow deeper rooting to access the
perature (Strathdee et al. 1995). Populations of some inver-
mineral horizons which were previously inaccessible (Na-
tebrate pests which defoliate large areas of Fennoscandian
delhoffer et al. 1992, Berendse and Jonasson 1992). Pro-
subarctic birch forests are controlled by the sensitivity of
jected increases in nitrogen fixation of 65-85% (Chapin and
over-wintering eggs to low temperatures (Tenow and Holm-
Bledsoe 1992) are also likely to minimize nitrogen limita-
gren 1987); warmer winters will likely lead to increased pest
tions to plant growth under projected climate changes.
populations and greater deforestation. Which species will
However, extrapolation of nutrient information over time
become harmful is unpredictable, but the probability of oc-
and space must be treated with caution. Enhanced release
currence is high. Such outbreak events could be an impor-
of nutrients does not necessarily lead to increased plant up-
tant factor determining the future pattern and timing of veg-
take and there is considerable variation between responses
etation change.
in different sites (Jonasson et al. 1993, Parsons et al. 1994).
Increasing insect outbreak may also result in greater fuel
Transport from lower latitudes of atmospheric pollutants,
loads, linking insect outbreak and wildfire. The coupling of
especially nitrogen compounds, may also influence nutrient
more frequent insect outbreaks and fire is likely to decrease
availability.
surface albedo because there will be less green foliage in
winter; this change in albedo may cause positive feedbacks
Permafrost and vegetation
to climate (Bryant et al. 1991).
A major cause of disturbance to vegetation is, and will in-
creasingly be, the dynamics of permafrost. Thawing of the
11.5.1.1.3. Vertebrates
active layer each summer allows plant roots to function.
Vegetation, and mosses in particular, restrict the degree of
Animals of the Arctic are ultimately dependent on plants for
soil warming in continuous summer daylight, but when the
energy and nutrients. Climate change can affect animals di-
upheaval of the permafrost and soil results in drainage and
rectly through an increase in extreme events such as drought
lack of moss cover, the permafrost can thaw at the surface
or ice layer formation over forage in winter and through
and retreat. This leads to soil slumping and active layer de-
slower processes such as changes in the amount and quality
tachment by which the soil can slide down the surface of
of food available. Altered winter snow conditions will affect
sloping permafrost at a rate of up to 5 m per week (Edlund
not only the availability of moisture, food, and shelter for
1989). At the coast, thermal abrasion of soil and permafrost
winter residents, but also the spring and summer moisture
can occur at 14 m per year.
regime. Quality and quantity of forage for herbivores can
A particular threat to Arctic biota from soil warming is
decline through an increase in plant defense mechanisms or
an increase in thermokarst disturbance. The disturbance to
by a change in species composition (Bryant et al. 1991).
vegetation from thawing permafrost opens up new habitats
Migratory mammals and birds can probably adjust more
for colonization and the low biodiversity of the tundra could
readily than non-migratory species to changes in the quan-
increase, with the risk of competition from immigrating spe-
tity and distribution of their food plants or prey in the Arc-
cies displacing the existing species. Slow plant growth and
tic, but vertebrate and invertebrate herbivores may face
sporadic recruitment of individuals to populations could re-
problems with changes in the quality of their food plants.
sult in recovery taking decades or centuries.
Long-term experiments by Chapin and Shaver (1996)
show warming of Arctic tundra is likely to result in replace-
Water stress
ment of cotton grass (Eriophorum vaginatum) by deciduous
Vegetation composition and structure in the Arctic are tied
shrub and, in particular, dwarf birch (Betula exilis for-
to soil moisture and nutrient availability. Actual effects of
merly B. nana ssp. nana). This vegetation change could be
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
751
very detrimental to populations of caribou and reindeer
myrtillus, of 12% for V. uliginosum, and of 27% for V.
(Rangifer tarandus). At the time of calving and in early lac-
vitis-idaea (Johanson et al. 1995b).
tation, these animals depend heavily first on flowers of cot-
Mosses as well as dwarf shrubs react to increased expo-
ton grass and, later, leaves of willow for a high protein food
sure to UV radiation. Mosses and lichens are particularly
source. High protein food is necessary for calf production
important components of Arctic vegetation, and are often
and survival and hence herd maintenance (Kuropat 1984).
critical to ecosystem function. Mosses mediate the exchange
This shift in species composition would therefore likely re-
of water and energy between soil and atmosphere while li-
sult in significant herd declines, especially in Siberia and
chens are the winter forage of caribou and reindeer (Rangi-
North America.
fer tarandus). Quite unexpectedly, growth of the moss Hylo-
Warming in high latitudes may also result in migration of
comium splendens was strongly stimulated by UV-B, pro-
taiga woody species into regions now occupied by tundra.
vided the moss received additional water (Gehrke et al. 1996).
Taiga woody species appear to be more heavily defended
The stimulation of annual growth in length by enhanced
chemically against mammalian herbivores than are tundra
UV-B (15% enhancement calculated for cloudless skies) was,
shrubs. An increase in the defense level of tundra vegetation
in three successive growing periods in the field, 15%, 31%,
would also stress herds of tundra herbivores such as caribou
and 27%. The stimulation of growth in length by UV-B was
(Bryant et al. 1991).
observed also in a greenhouse experiment. For in situ H.
splendens receiving only water naturally available, however,
there was no effect (first year of irradiation), or an inhibition
11.5.1.2. UV effects on terrestrial ecosystems
of growth in length (by 25% during the second year and
The literature on effects of UV radiation on Arctic terrestrial
18% during the third year).
ecosystems is limited and many assumptions are extrapo-
Thalli of lichens (Cladonia arbuscula, Cetraria islandica
lated from data on organisms in temperate regions (IASC
and Steroecaulon paschale) collected at Abisko (68°N) were
1995, Björn et al. 1997). In polar regions, the low air and
compared to thalli of the same species collected in southern
ground temperatures and low solar zenith angle, even during
Sweden (56°N). Experiments were carried out under 350,
the vegetation growth period, affect ecosystems in various
600, and 1000 ppm CO2. UV-B exposure increased the pho-
ways. Under unperturbed ozone and cloud conditions, UV-B
tochemical quantum yield of photosystem II as measured
irradiance is low. Consequently, Arctic plants have fewer
with pulse modulated fluorimetry, (F'm-Ft)/F'm, under low
protective pigments and are more UV-B susceptible than
CO2 (except late in the season, i.e. August), but not under
comparable plants from other regions of the world (Rob-
the highest concentration. The ratio was greater for lichens
berecht et al. 1980, Barnes et al. 1987). Repair processes
from Abisko than for those from southern Sweden (Sones-
are slower at cooler temperatures, while photochemical
son et al. 1995).
damage to DNA and other molecules can proceed as rapidly
as at higher temperatures, thus sensitivity to UV-B is more
11.5.1.2.2. Decomposition
pronounced at lower temperatures (Takeuchi et al. 1993).
Therefore, an increase in UV radiation is an ecological con-
The relative weight of indirect effects of UV-B on decompo-
cern in the Arctic, and further ozone depletion is a potential
sition (via changes in litter chemistry) versus direct effects
threat.
(via photodegradation of lignin, etc.) are liable to differ be-
tween tundra habitats. In High Arctic habitats and fellfields
with open plant canopies, direct effects may outweigh indi-
11.5.1.2.1. Dwarf shrubs, mosses, and lichens
rect effects when litter intercepts UV-B. In closed vegetation
The responses of subarctic plants to UV-B are subtle and
regions of the mid- and subarctic, direct effects of photochem-
sometimes surprising, vary from species to species, and can-
ical degradation may predominate when living leaves inter-
not be predicted without detailed experimentation. There is
cept UV-B (Moorhead and Callaghan 1994). Whichever path-
some evidence that stem growth inhibition from increased
way prevails, alterations in nutrient availability to plants are
UV-B in perennial plants increases over time. Although it is
significant in the nutrient-limited ecosystems of the Arctic.
too early to make any detailed statements, the effects of al-
Exposure of V. uliginosum leaf litter to enhanced UV-B
tered UV-B radiation on certain plant species is expected to
changes the litter composition toward a decrease in cellulose
have an impact on complex ecological interactions.
and the cellulose/lignin ratio and an increase in tannins
Growth and morphology of dwarf shrubs exhibit changes
(Gehrke et al. 1995). UV-B exposure during decomposition
in leaf thickness and relative shoot growth under increases
decreases the proportion of lignin and decreases fungal colo-
in UV-B radiation. Species-specific changes have implications
nization and total microbial respiration. Of three fungal
for plant community composition and plant nutritive value
species investigated, Mucor hiemalis and Truncatella trun-
for herbivores. In UV enhancement experiments, the leaves
cata were more UV-B sensitive than was Penicillium brevi-
of Vaccinium vitis-idaea became thicker (by 4 to 9% de-
compactum (Gehrke et al. 1995). Leaf litter from treated
pending on year) and those of the deciduous dwarf shrubs
(UV-B supplemented) V. myrtillus plants is decomposed
thinner (by 4 to 10% depending on year and species) (Jo-
more slowly by microorganisms than is litter from control
hanson et al. 1995a). Enhanced UV radiation caused in-
plants (Gehrke et al. 1995). The increase in UV-B radiation,
creases of 24% to leaf dry weight and 29% to leaf area for
although possibly lethal for some soil microorganisms, will
V. uliginosum (Johanson et al. 1995b).
have little direct effect because of its very limited transmis-
The relative longitudinal shoot growth (i.e. shoot growth
sion into the soil. Changes in plant chemistry in response to
under enhanced UV-B divided by growth of the same shoot
UV-B will probably have much greater influence on soil pro-
during the year before application of enhanced UV-B) was
cesses (Caldwell et al. 1989, Gehrke et al. 1995).
reduced in Empetrum hermaphroditum by 14% after one
Positive responses of mosses to enhanced UV-B could
year of enhanced UV-B and by 33% after two years. For the
counteract future impacts of climatic warming, but, as in
Vaccinium species, no significant effects on longitudinal
the example of H. splendens, predictions of future water
growth of shoots were found after one year of irradiation,
balance under warming in the Arctic suggest greater stress
but after two years there was a reduction of 14% for V.
which would result in repressed growth due to UV-B.
752
AMAP Assessment Report
11.5.1.2.3. Animals
11.5.2.1.2. Larger animals
Animals are likely to be more affected by the impact of
Climate change is likely to affect the habitats and therefore
changing UV-B levels on their food supplies and general en-
the areal extent of larger animal populations. Sea ice pro-
vironment than by physiological harm. Nevertheless, ocular
vides critical habitat for ringed seals (Phoca hispida), walrus
damage and systemic damage may harm larger mammals,
(Odobenus rosmarusa), and polar bears (Ursus maritimus).
particularly under large changes in UV-B. Increased UV-B
Changes in sea ice will affect each of these marine mammals
could lead to a deterioration in the quality of forage which
in various ways. Annual variations in sea ice distribution
in turn could lead to nutritional stress on herbivores. For
and abundance affect ringed seal and polar bear reproduc-
example, UV-B is causally linked to synthesis of certain phe-
tion and survival (Stirling and Derocher 1993). Changes in
nolics that may act as feeding deterrents or toxins to herbi-
distribution and abundance of polar bears as a result of cli-
vores including mammals (Caldwell et al. 1989). Over the
matic fluctuation have been demonstrated for a population
past 10 years, an increase in tannin and other phenols in
of polar bears in Greenland (Vibe 1967). Polar bears at the
some Arctic species has been linked to a decline in produc-
southern extent of their range are likely to be most severely
tivity of moose (Bo and Hjeljord 1991) and might be associ-
affected. Climate warming may impact the ability of polar
ated with a decline in productivity of caribou. It remains un-
bears to successfully hunt seals by reducing access to seals
known whether the increase in phenolics is from an increase
because of a decrease in sea ice surface and seal population.
in sunny days and a resultant increase in PAR or from an in-
crease in UV-B or interannual differences in temperature.
11.5.2.2. Photochemical effects of UV:
Dissolved organic matter
11.5.2. Aquatic ecosystems
Dissolved organic matter makes up the bulk of organic mat-
11.5.2.1. Climate change and marine ecosystems
terial in both lakes and oceanic water. It also supplies available
Climate change will have a profound impact on the marine
carbon (Walsh 1995, Wheeler et al. 1996). Because of its ab-
ecosystem through changes in temperature, sea ice, cloud
sorptive properties, dissolved organic matter (measured as dis-
cover, and ocean circulation patterns. The effects of warm-
solved organic carbon, hereafter DOC) in the water column
ing ocean temperatures and decreased extent or thickness of
influences how well biota are shielded from UV exposure (Scul-
sea ice on primary productivity in marine ecosystems are un-
ly and Lean 1994, Schindler et al. 1997, 1996b). Autochtho-
clear. Sea ice thickness and extent has a bearing for the com-
nous DOC is generated via excretion by plants and animals
munities of phyto- and zoo-plankton that utilize it as a spe-
within the aquatic ecosystem and blocks very little UV (Cur-
cific habitat (Horner 1985). A possible consequence of more
tis and Adams 1995). In contrast, allochthonous DOC sup-
open water and thinner ice is increased primary productivity
plied from terrestrial sources is highly colored and is the prin-
which would affect higher trophic levels. Conversely, reduc-
cipal UV-attenuating substance in marine and fresh waters.
tion in the stratospheric ozone layer and increased UV pene-
The biogeochemical cycling of DOC is partially regulated
tration as discussed in section 11.4.3 are likely to have ad-
by UV radiation. In contrast to earlier beliefs, it has been
verse effects on productivity. Organisms higher up the food
shown during the last decade that dissolved humic matter
chain will also be affected by warmer waters; community
(DHM), largely of terrestrial or littoral origin, is available to
composition of marine fish may be altered, which would af-
pelagic bacteria, making it an important carbon source in ad-
fect predatory mammals, birds, and commercial fisheries.
dition to autochthonous organic matter (Tranvik 1988, Hes-
sen et al. 1990, Moran and Hodson 1994). Since DOC ab-
sorbs light, particularly UV radiation, radiation can be ex-
11.5.2.1.1. Marine fish
An increase in ocean water temperatures is expected to af-
fect species distribution and population numbers, thereby
altering species composition in marine waters. The Barents
Sea can be used as a model to show the effects of warming
on fish populations since there is historical documentation
UV-light
CO2
of the effects of relatively warm and cool temperatures. In
the Barents Sea, where temperature is the limiting factor for
Bacteria
population distribution of many fish species, warming will
Photooxidation
Photolysis
allow new areas to be colonized by cod (Gadus morhua),
of DHM
of DHM
Humic
Low Molecular
herring (Clupea harengus), haddock (Melanogrammus ae-
CO2
Matter
Weight DOC
glefinus), and Greenland halibut (Reinhardtius hippoglos-
(DHM)
soides), among others. In contrast, herring and gadoids (cod
and haddock) in the North Sea might slowly decline as they
are pushed north out of important feeding and spawning
grounds by competing species from the south. Mackerel
(Scomber scombrus) and sardine (Sardina spp.) may increase
Figure 11·22. Illustration of the role of UV radiation in the biogeochem-
and the area become more Mediterranean-like in its fish
ical cycling of DOC. Under the influence of solar UV light, dissolved humic
populations (Øiestad 1990). Salmonids may benefit from
matter (DHM, organic matter largely derived from terrestrial ecosystems)
changes in both ocean temperatures and stream habitat (see
in streams, lakes and coastal marine waters can be transformed to CO2.
This can occur through purely abiotic photooxidation of DHM or through
section 11.5.2.4.2).
photolysis (cleavage) of DHM into smaller molecules more easily utiliz-
Predicted climate changes that cause increased ice extent
able as a substrate for aquatic bacteria than the original high molecular
and cooling in some marine areas might decrease habitat for
weight DHM. Increased availability of bacterial substrate then leads to
marine fish species. Cooling deep water could limit gadoid
enhanced CO2 production through bacterial respiration. However, direct
negative effects of UV light on bacteria, causing reduced growth and res-
production, much as occurred in the Norwegian and Barents
piration, also influences the process. The balance between these separate
Seas from around 1900 into the 1920s (cf. Øiestad 1990).
processes in nature is unknown.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
753
Solar
Climatology
UV-B/A
Climatology
e.g. cloudiness &
Light
e.g. cloudiness &
global warming
global warming
CO
-
2
HCO3
CO2
CO2
release
Zooplankton
Phytoplankton
Humic OM
(-)
(-)
Viruses
race Gases
T
(-)
CO2
HMW
HMW
race Gases
Flagellates
LMW
Algal
Allochthonous
T
(-)
DOM
Metabolites
DOM
direct
Exoenzymes
O2
uptake
Photolysis
CO2
CO2
Bacteria
LMW DOM
+ uptake
Organic Matter
Photolysis
Figure 11·23. Illustration of the role of UV radiation in various light-dependent processes. Natural UV radiation impacts the numbers, distribution and
activity of several aquatic ecosystem targets and thus, theoretically, their interactions (adapted from Karentz et al. 1994). There is a large uncertainty as
to the magnitude of UV effect and the sign (feedback/feedforward) of the UV-dependent loops between the ecosystem/atmospheric components.
pected to transform autochthonous and allochthonous DOC
DOC increases the removal of DOC from freshwater. Acidi-
abiotically. There are two main pathways (see Figure 11·22):
fication compounds these effects (Schindler et al. 1997).
1) production of Dissolved Inorganic Carbon (DIC)* through
Apart from its optical properties, DOC also influences wa-
photooxidation of DOC (Miles and Brezonik 1981, Kulo-
ter column chemistry by chelating trace metals such as iron,
vaara and Backlund 1993, Frimmel 1994, Salonen and Vaha-
manganese, copper, and aluminum that are either essential nu-
talo 1994) and, 2) production of low molecular weight or-
trients or can even be toxic in their free state (e.g., Al). UV ra-
ganic compounds and CO through photolysis of DOC (Mop-
diation can alter the redox state of trace elements via forma-
per and Stahovec 1986, Kieber et al. 1989, Backlund 1992,
tion of reactive oxygen species. Such changes will affect the
Kulovaara and Backlund 1993, Allard et al. 1994, Conrad
solubility and availability of biogenic elements for organisms.
and Seiler 1980, Miller and Zepp 1995).
The net result of exposure of DOC to radiation would,
11.5.2.3. UV and the marine ecosystem
in both cases, be increased DIC production and a higher
turnover rate of DOC, as Pathway 1 would directly produce
An increase in UV radiation due to stratospheric ozone de-
DIC and Pathway 2 would supply pelagic bacteria with
pletion has measurable, direct impacts on the marine envi-
readily utilized substrates, increasing bacterial production
ronment. Light-dependent processes in phytoplankton (i.e.,
rate, biomass, and rate of respiration, i.e., CO2 production.
plant photosynthesis, photoinhibition, phototaxis, photo-
Mopper et al. (1991) suggest that photochemical degra-
protection, trace gas emission, etc.), animals (i.e. vision, be-
dation is the rate-limiting step for the removal of a large
havior and reproductive cycles, sensitivity to epidermal dis-
fraction of oceanic DOC. Since oceanic DOC is one of the
ease, etc.), as well as microbial and photochemical transfor-
largest global carbon reservoirs, increases in its rate of cy-
mations of various organic molecules and redox states of
cling could potentially significantly increase atmospheric
metals are all regulated by the spectral composition of the
CO2 (Wetzel et al. 1995). In addition, model calculations in-
light field (Figure 11·23) (cf. IASC 1995, SCOPE 1992,
dicate that increased atmospheric CO2 can cause the forma-
1993, UNEP 1991, 1994, IASC 1995). Owing to seasonal-
tion of an Arctic ozone hole (Austin et al. 1992), further in-
ity, depth refugia, vertical mixing, and pronounced natural
creasing the positive feedback between increased UV-B and
annual variability, detection of early signs of increased UV
CO2 in the atmosphere. If UV light, and especially UV-B, is
stress require careful, focused experiments.
primarily responsible for photooxidation and photolysis of
Special attention has been paid to the sensitivity of pri-
DOC, then increased UV-B radiation would cause an in-
mary production in marine ecosystems to UV radiation be-
crease in photo-oxidative and respiratory production of
cause planktonic algae are the base of the marine food web
DIC in surface waters (lakes, wetlands, rivers, marine wa-
and they constitute an important CO2 sink in the global car-
ters), escalating CO2 transport to the atmosphere and thus
bon cycle. The considerable dilution of Arctic Ocean surface
reinforcing the greenhouse effect.
waters by seasonal melting of ice edges and year round fresh-
In ocean waters, DOC may increase under global warm-
water inflow causes pronounced stratification of the upper
ing due to the thaw of terrestrial permafrost which might
mixed layer (30-50 m thick) in the Arctic Ocean at all times
increase run-off to the Arctic Ocean in some areas (Jones
of year (cf. Barry 1989). This is in striking contrast to other
and Briffa 1992, Goryachkin et al. 1994). However, climatic
major world oceans except near Antarctica (Smith et al.
warming may decrease DOC in freshwater systems and oceans
1992). Coastal waters of the Arctic Ocean carry high loads
due to a reduction of export of DOC from terrestrial and
of particulate and dissolved organic matter (comprised of
wetland catchments as reduced precipitation and increased
minerals, dissolved organic carbon, chelating metals, and
evaporation cause streamflow to decrease and water tables
humic substances recalcitrant in nature). As a result of con-
to fall. An increase in UV-B concurrent with a decrease in
straints on nutrient availability, planktonic organisms and
* DIC is defined as the sum of dissolved CO
2
2 , H2CO3, HCO3 and CO3 , but not including CO, which has also been shown to be produced photo
chemically from DOC in water (Conrad and Seiler 1980, Miller and Zepp 1995)
754
AMAP Assessment Report
larvae are confined to the upper reaches of the water column
radiation are uptake, assimilation, mineralization, and nitro-
and thus may be particularly vulnerable to increased UV ra-
gen fixation, since all of these occur in the upper part of the
diation, especially in the spring months when ozone deple-
water column. Phytoplankton productivity in the Arctic
tion appears most severe and when migratory species of ani-
Ocean varies widely from the least productive Central Polar
mals come to breed in the Arctic Ocean and its freshwater
Basin to ice-free coastal upwelling areas and episodic blooms,
tributaries.
especially red tides, during periods of spring/summer stratifi-
Each marine plant ecosystem, whether free-floating, em-
cation (cf. Andersen 1989, Smith and Sakshaug 1990, Smith
bedded in the undersides of ice, or attached to the surface
and Grebmeier 1994).
of the sediments, serves the needs of different sets of ani-
Little effort has been made to understand the effects of
mals, plays an important and often distinct role in the bio-
UV-B on in situ primary production in the Arctic Ocean.
geochemistry of the Arctic Ocean, and is likely differently
Effects of UV-B radiation on in situ primary production in
affected by changing UV climatology over Arctic latitudes
the oceans near Antarctica have been examined by incubat-
(IASC 1995). UV also directly affects the vitality and chemi-
ing either unialgal cultures or the ambient natural popu-
cal activity of viruses, bacterioplankton, protozoans, and
lations. By modeling the results from these experiments,
microzooplankton (Herndl et al. 1993, Hunter et al. 1979,
often based on irradiation from inside and outside an
Williamsen and Zagarese 1994, Helbling et al. 1995, Mül-
ozone hole, scenarios for reduced primary production have
ler-Niklas et al. 1995, Vetter 1996). Because the amount of
been calculated (e.g., Smith et al. 1980, 1992, Smith and
UV-B reaching marine plants varies, the effects of increased
Baker 1982, Holm-Hansen et al. 1993b, Cullen et al. 1992,
UV-B will also vary. In the long run, some organisms may
Cullen and Neale 1994). In general, it is assumed that UV-
adapt to enhanced UV-B radiation and thereby a succession
B irradiation reduces total water column photosynthesis by
toward more tolerant species will occur. Adaptive mecha-
5-6% under normal Antarctic ozone levels, while during an
nisms such as synthesis of screening pigments, capacity to
ozone hole the reduction can increase to 6-18% (cf. Scho-
avoid UV-B, and increased enzymatic repair might reduce
field et al. 1995). It is evident that ambient radiation (PAR,
the inhibitory effects of UV-B if phytoplankton are exposed
UV-A and UV-B) during normal levels of stratospheric
during longer time periods (Karentz 1994). However, the
ozone inhibits primary production close to the surface, and
sensitivity to UV-B radiation and the adaptive mechanisms
thereby enhanced UV-B radiation will increase the UV-B
differ widely between species.
dependent inhibition. There are no indications that similar
scenarios could not be expected in the Arctic. Recent re-
search indicates that post-bloom phytoplankton communi-
11.5.2.3.1. Primary producers
ties from northern Norway are more sensitive to ambient
Physiological responses of primary producers to UV have
UV-B radiation than those from the southern ocean (Helb-
been observed in cell DNA, protein, nitrogen metabolism,
ling et al. 1996).
lipid metabolism, motility, screening pigments (mycosporine-
The above-mentioned conclusions are all based on short-
like amino acids), photosynthetic machinery (photosystem
term experiments but results suggest that UV-B radiation
II, the carboxylating enzyme, the Calvin-Benson cycle), and
will induce changes in species composition that will cause
repair mechanisms (e.g., Holm-Hansen et al. 1993a, Vincent
long-term effects at a community level. Unfortunately, ex-
and Roy 1993, Häder et al. 1995). UV can inhibit motility
perimental data describing the long-term effects of UV-B ra-
in flagellated phytoplankton (Ekelund 1990, Häder 1993)
diation on phytoplankton communities are very limited, but
and alter cell composition (Vosjan et al. 1990, Goes et al.
changes in species composition of phytoplankton communi-
1994, 1995) and cell structure (Karentz et al. 1991, Beh-
ties have been shown in long-term experiments with natural
renfeld et al. 1992). UV-B radiation is known to reduce
phytoplankton communities (Worrest et al. 1981, Helbling
short-term growth rates and primary production of a num-
et al. 1992, Wängberg et al. 1996, El-Sayed et al. 1990).
ber of polar aquatic phytoplankton communities (cf. Holm-
Evaluation of the effects of UV-B irradiation on the marine
Hansen et al. 1993a, Vincent and Roy 1993, Karentz et al.
ecosystem lack long-term experiments on the biological and
1994, Prézelin et al. 1994a, 1994b, 1995, 1996, 1997, Bou-
chemical processes in planktonic food webs. Not enough
cher and Prézelin 1996).
data are available to make a valid risk assessment (Wäng-
There is a nonlinear relationship between changing UV
berg et al. 1996).
climatology and UV sensitivity of natural phytoplankton
Experiments with natural assemblages of phytoplankton
communities, making the accuracy of future spectral model-
using additions of 15N-labeled nutrients have shown nitro-
ing of UV effects on primary production dependent upon the
gen uptake and assimilation to be negatively affected by UV-
availability of in situ BWFs (see section 11.4.3.1) for the
B (e.g., Döhler et al. 1991, Döhler 1992). Enhanced UV-B
aquatic ecosystem under study. To extrapolate results of en-
might then increase the nitrogen demand in phytoplankton
hanced UV-B on phytoplankton growth into consequences
because of protein degradation. Proteins are known to be
of increased UV-B radiation, the correct BWF needs to be
absorbers of UV-B radiation (Karentz 1994); an increase in
applied. Results from Antarctica show that BWFs vary on
protein degradation followed by resynthesis in order to re-
time intervals as short as two hours, reflecting diel periodi-
place UV-B-sensitive proteins could thus be expected during
city in both cell biology and the magnitude and spectral bal-
UV-B exposure (Cullen and Neale 1994). Nitrogen-depleted
ance of the natural light field. Also, BWFs differ significantly
phytoplankton might therefore be more susceptible to UV-B
over the austral springtime and may reflect different light
radiation. In addition, UV has a regulatory effect on the up-
histories, taxon-specific biology, or changing physiological
take of inorganic nitrogen and phosphorous required for
states of the phytoplankton communities.
growth (Dohler 1992, Tyagi et al. 1992, Behrenfeld et al.
The Arctic and subarctic surface waters exhibit low nutri-
1995). On longer time scales, if phytoplankton fix less car-
ent (nitrogen, silicate, and phosphate) concentrations which
bon, grow slower, or increase rates of organic excretion in
usually become exhausted during summer. Both nitrate and
the presence of UV radiation, there may be indirect conse-
silicate have been considered to limit primary production
quences to the biogeochemical cycling of nutrients and there-
(Kristiansen and Farbot 1991, Harrison and Cota 1991).
fore to the vitality of higher trophic levels within aquatic
The nitrogen transformations liable to be affected by UV-B
ecosystems.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
755
Phytobenthos and macroalgae play important roles in
Herbert and Emery 1990, Karentz et al. 1991). Increased UV
the extensive coastal areas of the Arctic Ocean, contributing
could cause a change in species composition and thereby a
50% of total primary production of shelf systems. Macro-
succession that may alter the planktonic food webs.
algae produce organohalogens that are released to the water.
It has been suggested that these volatile gases play a role in
11.5.2.3.4. Invertebrates
trace gas chemistry of the atmosphere (Gschwend et al.
1985). Hence, the influence of UV radiation on macroalgal
Little research has been done on the responses of inverte-
growth might have various secondary consequences of con-
brates to enhanced UV in the Arctic and few publications
cern for climate change issues (IASC 1995). Both laboratory
are available on invertebrate responses to UV radiation in
studies under artificial light sources and field studies under
any region of the globe. Exceptions are the work of Hatcher
natural light suggest that UV radiation inhibits production
and Paul (1994) and Newsham et al. (1996) which show
and growth in many different benthic, lithotrophic, and
that invertebrate herbivores can be affected both by changes
macroalgal taxa, as well as seagrasses, but that the magni-
in food plant quality and by apparent artifacts associated
tude of the impact may well vary between taxa and as a
with methods of increasing UV exposure. Recent studies
function of a photoadaptive state (Trocine et al. 1981, Wood
suggest that UV inhibits blackfly (Simulidae and Diptera)
1987, Larkum and Wood 1993, Evens et al. 1994, Grobe
colonization in boreal and alpine streams (Bothwell et al.
and Murphy 1994).
1994, Williamson et al. 1996).
11.5.2.3.2. Bacteria
11.5.2.3.5. Fish populations
The capacity of bacteria to resist or adapt to UV-B irradia-
Fish species of highest risk in Arctic areas could be those
tion varies widely. Ambient UV-B irradiation can inhibit
species that settle in shallow waters in the early spring and
bacterial DNA replication, protein synthesis, and degrada-
species with pelagic drifting eggs and larvae. Many impor-
tive enzyme activities in some species (Herndl et al. 1993,
tant fish stocks (i.e., herring, pollock, cod, and salmonids)
Helbling et al. 1996, Müller-Niklas et al. 1995). Other gen-
spawn in fully exposed shallow waters where they are ex-
era seem to have an extreme resistance to UV-B irradiation
posed to epidermal and pineal effects that may be aggra-
and some are even stimulated in population growth by low-
vated by UV-B radiation. Fish larvae are generally very sus-
level exposure (Herndl et al. 1993, Karentz 1994).
ceptible to UV-B damage, and even ambient solar radiation
Photochemical degradation of DOC, causing increased
has the potential to affect their viability (Hunter et al. 1979).
availability of low molecular weight compounds, could also
The larvae of several fish species, including salmonids and
stimulate bacterial activity. Lindell et al. (1995) and Wetzel
herring, are particularly vulnerable to UV radiation since
et al. (1995) found enhanced bacterial numbers and cell vol-
spawning occurs in very shallow waters and the larvae re-
umes concomitantly with a reduction in DOC when expos-
main in the vicinity during their early stages of growth. Skin
ing natural limnic water to moderate UV-B irradiation; they
and gill lesions caused by UV-B radiation have been observed
interpreted this to be a result of enhanced availability of
in adult fish in lower latitudes (Robberts and Bullock 1981,
bacterial substrates. The net effect of these processes may
Bullock 1985, Bullock and Coutts 1985). Research needs to
depend on the humic content and absorption of the water
be carried out on Arctic organisms that have evolved in low
(Lindell et al. 1995), although the balance between these
UV environments. Important for evaluating the potential ef-
effects needs to be further evaluated before the long-term
fects of UV radiation on fish are timing of the spawn, the
response of an ecosystem can be determined (Karentz et al.,
distribution of species within the water column (Holm-Han-
1994). Heterotrophic bacteria compete efficiently with phy-
sen et al. 1993a), and the degree of vertical mixing in the
toplankton for nutrients (Goldman and Dennett 1991). An
water column.
enhanced nitrogen uptake relative to carbon fixation rates
Indirect effects of enhanced UV-B on the fisheries may
in natural plankton communities exposed to UV-B radiation
arise from changes in the planktonic food webs. Perturba-
during a one week experiment indicated a proliferating bac-
tions in food webs, however, are difficult to predict because
terial population. A 35-40% increase in thymidine incorpo-
they depend on the long-term adaptation of species and
ration activities has also been found in in situ enclosure
changes in community structure. Long-term experiments on
(5 m3) experiments with natural pelagic communities ex-
natural communities and ecosystems are warranted in order
posed to enhanced UV-B radiation for a fortnight. Although
to predict such changes.
individual phytoplankton species may not be harmed by or
may be adapted to increased UV-B radiation, phytoplankton
11.5.2.3.6. Larger animals
productivity in nitrogen limited waters might decrease due
to competition by bacteria for nutrients.
If the secondary productivity of the Arctic aquatic ecosystem
is challenged, then so too is the viability of sea birds and
land predators (i.e., seals, foxes, bears) which feed on aquatic
11.5.2.3.3. Zooplankton
organisms. The ocular effects of increased UV on anadro-
Natural irradiances of UV-B have been shown to be lethal to
mous fish and also birds, seals, and polar bears need to be
zooplankton; the numbers, survival and fecundity of their
considered as well (IASC 1995).
eggs and nauplii are reduced by short-term UV-B exposure
(Karanas et al. 1979, Damkaer et al. 1980, 1981, Damkaer
11.5.2.4. Climate change and Arctic freshwater
and Dey 1983, Ringelberg et al. 1984, Thomson 1986).
11.5.2.4.1. Climate change and Arctic lakes and ponds
That certain zooplankton will be able to adapt, or already
have protective systems, is suggested by the lower mortality
The amount of ice and snow accumulated on a lake or pond,
rates often encountered in zooplankton containing photo-
and the duration of ice cover, have profound effects on the
protective compounds such as astaxanthin, melanin, and
limnological characteristics of all northern aquatic systems.
mycosporine-like amino acids (Hairston 1976, 1980, Rin-
Especially in the High Arctic, where the entire ice free sea-
gelberg 1980, Ringelberg et al. 1984, Dunlap et al. 1986,
son may only be a few weeks in duration (Schindler et al.
756
AMAP Assessment Report
1974, Douglas and Smol 1994), even modest climatic warm-
Although several environmental gradients exist in the
ing can significantly increase the growing season.
Arctic, the location of Arctic treeline is climate-related,
Arctic ponds (sensu Sheath 1986) are defined as shallow
closely matching the mean July position of the Arctic Front
(generally < 2 m deep, and in many cases <1 m) systems that
(Bryson 1966). The presence or absence of coniferous trees
freeze to the bottom each winter. Fish and other vertebrate
that are associated with the Arctic treeline (e.g., spruce) have
predators are generally absent (with the exception of some
profound effects on the limnology of lakes draining these
migratory birds), and thus food webs are relatively simple.
catchments (MacDonald et al. 1993, Pienitz and Smol 1993).
These shallow ponds are a dominant feature of many Arctic
If the tree line moves north, patterns of wind mixing and
landscapes, yet few data are available on the limnology of
subsequent lake stratification may be altered by the presence
these systems (e.g., Hobbie 1980, Douglas and Smol 1994,
of trees (Rhodes and Davis 1995, Schindler et al. 1990), and
Havas and Hutchinson 1983).
DOC released from litter may increase (Schindler et al. 1992).
The most obvious effect of a warmer Arctic would be to
Changes in DOC can affect lake and pond water clarity and
increase pondwater temperatures. Because the vast majority
color, heat absorption, PAR and UV transmission, and nutri-
of these sites are so shallow, the ponds closely track ambient
ent cycling, which in turn affect the biota of the lakes (Sa-
air temperatures (Douglas and Smol 1994). With warmer
lonen et al. 1992, Schindler et al. 1990, 1992, 1996a, 1997).
temperatures and reduced ice cover, many aspects of the
Although generally considered rare in the Arctic, athalas-
pond system would change (Rouse et al. 1997, Douglas and
sic lakes (inland, saline, non-marine lakes) occur in some re-
Smol 1993, 1994). Reduced ice and snow cover may result
gions (Pienitz et al. 1992, Veres et al. 1995). These closed-
in a lengthened growing season, which will affect many
basin systems are especially sensitive to climate change be-
chemical, physical, and biological processes. In some lakes
cause slight alterations in evaporation and precipitation can
total annual primary production may increase, and more
greatly affect lakewater salinity levels, which then can strong-
complex periphytic assemblages may develop (Douglas and
ly influence the biota in these systems (Hammer 1986). Be-
Smol 1993, 1995). In deeper lakes, however, primary pro-
cause many of these lakes are shallow, the possibility exists
duction may decrease after break-up so that earlier break-up
of total desiccation for some systems with increased evapo-
would have a negative effect on production (Kalff and
ration rates.
Welch 1974).
Climatic warming could offset a positive feedback on
On the other hand, if precipitation does not increase sig-
light regimes and UV penetration in lakes, since warming
nificantly, evaporation from ponds would increase with cli-
and drought strongly reduces DOC and increases UV pene-
matic warming and the net water balance could be affected.
tration. This has been demonstrated for North American
As a result, pondwater conductivity values might increase,
lakes (Schindler et al. 1996a, 1997). These effects could in-
as might pondwater pH (Douglas and Smol 1994). A more
fluence Arctic lakes and coastal areas as well.
significant manifestation of increased evaporation rates
would be that some of the shallower ponds would desiccate
11.5.2.4.2. Climate change and Arctic rivers and streams
completely.
The relationship between lakewater acidity and climate
Climatic warming and resultant changes in precipitation
change may prove to be a significant determinant of Arctic
and glacial melt are likely to have a major impact on Arctic
ecosystems. Climate might control lakes via pH through the
streams and rivers and organisms inhabiting them. Thermal
effects on water renewal and relative yields of base cations
regimes in glacier-fed rivers could become colder while
and strong acid anions (Psenner and Schmidt 1992, Schind-
smaller streams could become warmer. Sediment and flow
ler et al. 1996a). Climatic warming and increased evapora-
regimes are likely to change as a result of glacier and per-
tion cause increased in-lake removal of sulfate and return of
mafrost melting, soil drying, and changes in spring breakup
base cations from sediments, both of which increase as wa-
(Oswood 1989).
ter renewal time increases; thus alkalinity increases. In areas
Some of the most obvious consequences of a warming cli-
that are strongly affected by acid rain, however, the effects
mate are increases in ice-free days and water temperatures in
of climatic warming and increased UV-B may increase cy-
non-glacial freshwater systems. The effect of a milder ther-
cling of DOC (Schindler et al. 1996a).
mal regime may change the biogeography of freshwater fish.
High Arctic lakes would similarly be affected by climatic
Increased water temperatures combined with year-round
warming, although maximum water temperatures would be
groundwater flow (from decreased permafrost) might change
less affected than in ponds, as deeper lakes have much higher
the suitability of streams for some fish species (Eaton and
thermal capacities. High Arctic lakes are characterized by
Scheller 1996).
extended snow and ice covers, with some lakes remaining
Studies at the freshwater ecosystem level are few. Allard
covered by a central float of ice throughout the short summer.
et al. (1994) noted that in the subarctic river Kalix (northern
Production in High Arctic lakes occurs whenever snow is
Sweden) there was a higher humic fraction DOC during win-
absent and the sun is above the horizon. Much of the annual
ter (dark period) than during summer. The authors interpret
production occurs under total ice cover, since many lakes are
this as an effect from photodegradation of dissolved humic
not clear of ice until late July or early August (Kalff and
matter in river water during the long daylight periods of the
Welch 1974, Welch et al. 1989). Strong winds and low snow-
Arctic summer.
falls generally keep lakes snow free for much of the year.
Temperature has been found to immediately affect pro-
11.5.2.5. UV and Arctic freshwater
ductivity. Some preliminary results from a littoral zone of a
boreal lake indicate higher primary production with 2°C rise
The effects of UV on Arctic freshwater will be highly depen-
in temperature, even in the absence of additional nutrient
dent on the transparency and DOC level of the water. Arctic
loading (Kankaala et al. 1994). However, Schindler et al.'s
freshwater may be expected to be altered from increased UV,
(1997) 20-year study found no change in production with
especially water of high transparency and low DOC. It may
2°C temperature increase in boreal lakes. Phytoplankton
be anticipated that most species and populations are locally
biomass declined in proportion to reduced phosphorus con-
adapted to present-day irradiance; however, plankton in
centrations and inputs caused by declining streamflow.
both Arctic and alpine waters are commonly light stressed
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
757
and exhibit low repair capacities (Luecke and O'Brien 1983,
11.6.1. Prehistorical and historical effects
Hebert and Emery 1990, Hessen et al. 1990). A further in-
of climate change
crease in UV-B could thus cause detrimental effects on vari-
ous taxa. Organisms in shallow ponds without depth refugia
Oceanographic and terrestrial factors related to indigenous
could, in particular, be susceptible to UV. Recent studies of
occupation of the Arctic center around cyclic resource abun-
UV-B effects on bacteria and zooplankton have been under-
dance or biological productivity. In Northwest Alaska, past
taken in experimental enclosures in the Canadian Arctic
periods of warming are associated with intensive occupation
(Lean unpubl.). Combinations of in situ and lab studies have
of coastal sites while cold periods supported inland occupa-
been performed with phytoplankton in subarctic alpine
tion by Iñupiat (Mason and Gerlach 1995). Ocean dynamics
areas (Hessen et al. 1995, Van Donk and Hessen 1996), and
and especially areas of nutrient upwelling influence location
particularly with zooplankton in the Canadian Arctic (He-
and hence availability of marine mammals and fish. Areas in
bert and Emery 1990) and Norwegian subarctic and High
close proximity to polynyas have historically and prehistori-
Arctic at Svalbard (79ºN) (Hessen 1993, 1994, 1996). The
cally been productive areas for human settlement, as have
work with phytoplankton demonstrates high susceptibility
inland areas supporting large numbers of caribou and fish.
of flagellum status, phosphorus uptake, growth rate, and cell
Changes in ocean dynamics resulting in changes in polynya
wall morphology. A particularly intriguing discovery is that
location have caused shifts in settlement patterns (Schleder-
UV exposure induces cell wall changes that reduce digestibil-
mann 1980, Mason and Gerlach 1995). Sudden decreases in
ity of phytoplankton for zooplankton (Van Donk and Hes-
caribou populations or sudden changes in caribou migration
sen 1995). The zooplankton studies focus on the widespread
routes have forced indigenous peoples to abandon some
key genus Daphnia, and studies on melanic (UV tolerant)
areas for more productive ones; some past changes in cari-
and hyaline (UV susceptible) natural clones have been per-
bou concentrations have been attributed to climate change.
formed. These studies are intimately linked to population
Variations in climate may crucially alter societies living in
genetics and evolutionary history of these clones.
regions which are environmentally and climatically marginal
as certain economic activities, particularly those based on
agriculture, become inviable (Parry 1978). In pre-twentieth
11.6. Effects of climate change and
century Iceland, for example, periods of cooling were fre-
UV radiation on Arctic peoples
quently associated with poor harvests, and subsequent mal-
nutrition and death among livestock and humans (Ogilvie
An understanding of contemporary patterns of settlement
1982, 1984). In Greenland, the Norse settlement was aban-
and resource use combined with evidence from historical
doned around 1350 AD. Computer modeling of the climate
and archeological records can help estimate the magnitude
and agricultural data indicate that a combination of reduced
of potential impacts of climate change to Arctic communi-
summer growing season for fodder and an extended winter
ties. To the extent that Arctic peoples continue to harvest
feeding period for imported European domestic animals may
plant and animal foods, live permanently or seasonally on
have placed the Norse economy under extreme stress (Buck-
coastal spits and along river banks and lake shorelines, and
land et al. 1996, Barlow et al. 1997). Inuit living in the same
use snow mobiles and dog sleds for transportation, climate
area of Greenland, with seal hunting forming their main
changes will directly impact their lives.
economic base, continued to thrive. From these and other
Climate change affects people on different scales; glob-
examples, it is possible to infer that dependence upon local
ally, regionally, and subregionally. While a general warming
resources and the vulnerability of local environments and
of the Arctic is predicted, regional weather patterns are prob-
geography to changes in parameters such as precipitation,
ably more important to human use and habitation as some
temperature, sea level, and ice cover can lead to large-scale
areas will become cooler while others warm. Should glaciers
shifts in resource use and settlement patterns in the Arctic.
and ice sheets melt significantly over the coming decades, sea
level rise will impact village location, transportation, tourism,
11.6.2. Settlement and resource use
water resources, and other facets of Arctic life. If climatic
warming results in less sea ice and better access to northern
Indigenous patterns of resource use and settlement location
oceans, it is reasonable to project that activities such as ship-
are based on stable patterns of resource availability. Settle-
ping, mining, and on-and offshore oil development will in-
ments have been established where food, water, shelter, and
crease. To understand the impacts of climate change on
transportation are reliable. Today hunting and fishing camps
communities and regions, it is important to identify associ-
are set where resource abundance can be predicted for certain
ated regional policy concerns (Yin and Cohen 1994).
times of the year; as resource availability shifts so do hunt-
Potential effects of climate change on settlement and re-
ing and fishing camps. While today many would describe the
source abundance can be inferred from the past record. To
economy of northern peoples as mixed, the robustness of the
the peoples living in the North, normal seasonal variation has
indigenous economies depends on their abilities to accom-
always been considerable, commonly demanding or enabling
modate the annual variability in local plant and animal re-
routine changes of settlement area, social grouping, house
sources as well as the physical environment (Langdon 1986).
form, subsistence activity, mode of transportation, and diet.
Many coastal settlements in the Arctic, particularly in
While access to modern resources may mitigate the effects of
Alaska and Russia, are on low-lying coastal plains and river
climate change, impacts upon the ability of northern popula-
deltas. Storms during summer and fall have historically
tions to continue traditional ways of life might be overwhelm-
caused damage to these communities. Coastal erosion
ing. Establishment of permanent villages and towns may also
threatens several villages in Alaska, and some have already
compound the effects as people today are tied to villages and
moved to more protected areas. Changes in ice formation
less able to move with shifting resources. In some areas then,
and breakup could increase flooding along rivers. A rise in
climate change might further remove people from culturally
sea level will threaten many more communities as coastal
important hunting, gathering, and fishing activities and asso-
plains and spits are flooded and the geography of major
ciated spiritual and social relationships, knowledge transfer-
river deltas transformed. Detailed information on commu-
ence, and other traditional economic endeavors.
nity response to floods is provided by Newton (1995).
758
AMAP Assessment Report
Loss of permafrost from climate warming may also
be shaded by other factors besides climate change, including
threaten existing structures such as buildings, underground
global economic forces, technological changes, and political
storage, roads, and pipelines. Areas that presently have large
developments. This is evident in the Mackenzie Basin Impact
amounts of massive ground ice could become particularly
Study (MBIS) case from northwest Canada (Cohen 1997).
unstable, causing increased problems for existing roads and
buildings and new construction. At the same time, construc-
11.6.3.1. Commercial fisheries
tion methods may become easier in some areas as soils thaw,
dry out, and become more stable.
The effects of both warmer and cooler ocean temperatures
Precipitation and river flow are also important considera-
on fish populations are discussed in section 11.5.2.1.1.
tions for village location. Temperature and humidity changes
A warmer ocean could bring large economic benefit to Arc-
may affect both the energy balance of ecosystems and the
tic residents if fish populations increase. However, some
availability of water and snow cover. Much of the Arctic re-
populations might decline as species composition changes.
ceives little precipitation, and a decrease in snowfall or rain
Aquaculture would probably profit from a temperature in-
could reduce water supplies for villages and towns. In the
crease. However, toxic algae and new fish diseases might
large areas of coastal plain and wet tundra, an increase in
cause increasing problems in a warmer ocean as might occa-
precipitation could make lands unusable for settlement.
sional episodes of high surface water temperatures (Øiestad
Changes in snow cover and sea ice would also affect travel-
1990). Beneficial influences on wild salmon populations
ing conditions over the land and sea respectively, altering the
might come from river and stream temperatures, flow rate,
ability of hunters to reach other villages and hunting loca-
and sediment amount. As discussed in section 11.5.2.4.2,
tions in winter. Increased precipitation and run-off could
some fish species, including salmonids, are likely to benefit
also interfere with springtime travel.
from effects of a warming climate. In some areas where
Thus, climatic changes would impact geophysical and
ocean temperatures decrease and the extent of sea ice ex-
biological processes. Changes in air and water temperature,
pands fisheries would be expected to collapse (Øiestad 1990).
precipitation, and storm patterns could affect availability of
fish, land and marine animals, and plant foods to humans.
11.6.3.2. Reindeer herding
Indigenous hunting strategies are the result of the interplay
of complex variables such as the distribution of numerous
In Fennoscandia and Eurasia domestic reindeer herding is an
game species, dietary needs, transportation possibilities, and
important livelihood among indigenous pastoralists. It is an
energy expenditures of different hunting forms (Freeman
important food source, a foundation of cultural heritage,
1984). Animal and fish species which often seem abundant
and a vital economic resource. Changes to reindeer herding
are largely composed of seasonal migrants to specific feeding
caused by increased precipitation and temperature and resul-
grounds where food production can be intense but short.
tant changes in vegetation composition and nutritive value
Changes in vegetation and precipitation could shift the
are difficult to predict. Displacement of high quality forage
migration of terrestrial mammals and alter the breeding and
by low quality or non-food species as described in section
molting areas of birds. Cooling or warming of rivers and
11.5.1.1 may severely reduce grazing lands impacting the
lakes would probably affect the distribution and abundance
economies of reindeer herders (Bryant et al. 1991). Changes
of all types of freshwater and anadromous fish.
in timing of break-up or increased river levels could make it
Marine mammals are important cultural and dietary re-
difficult to move animals between pasturage.
sources for indigenous people of the Arctic (Lantis 1938,
Worl 1980). Human exploitation of marine mammals is de-
11.6.3.3. Transportation
pendent on sea ice conditions, including lead and polynya
formation, ice extent, and location of shorefast ice. At the
Warmer temperature and a possible reduction in seasonal
same time, the population density of many marine mammals
and annual sea ice cover may increase the opportunities for
including ringed seals and walrus is positively correlated
shipping in the Arctic through the Northern Sea Route and
with the distribution and condition of coastal sea ice (Mac-
the Northwest Passage as well as by increasing ice-free days
Laren 1961). Climate change might cause ringed seals,
for some harbors. At the same time, regional decreases in
whales, or walrus to migrate in new paths, thereby signifi-
ocean temperature may have the opposite effect and close
cantly affecting subsistence harvesting. All of the above
off areas to year-round shipping. Changes to regional ship-
changes may directly impact the way indigenous peoples are
ping practices including cruise ships will also depend on re-
able to obtain food resources and maintain their economies.
gional economic activity, which may be affected by a change
Increases in off-shore oil development and shipping due
in ocean access or other climate-affected parameters.
to a decrease in sea ice might affect populations of marine
mammals in general. Of particular concern are culturally
11.6.3.4. Forestry
and nutritionally important animals such as ringed seals,
whales, walrus, and polar bears (Stirling and Calvert 1983,
The northern treeline is expected to move north as the cli-
Stirling 1988, Stirling and Derocher 1993). An increased
mate warms and conditions become more favorable (Mac-
ability for humans to live in the north may also increase
Donald et al. 1993, Sveinbjornsson et al. 1992). In areas of
human-bear interactions, and bears could be pushed out of
nutrient availability trees are also expected to grow more
parts of their present range.
quickly; this could supply more harvestable trees in the fu-
ture. However, as a result of decreased summer precipitation
and drier foliage and leaf litter, outbreaks of defoliating in-
11.6.3. Economic activities
sects might increase resulting in increased forest fires as dis-
A warmer climate will impact communities economically and
cussed in section 11.5.1.1.2.
socially. Accounting for these factors requires consideration
Fire may have beneficial effects if the intensity of fire is
of the nature of Arctic communities, which often include
not too great. Fire can fertilize the forest floor and stimulate
both wage and non-wage (subsistence) economies and life-
growth of early successional deciduous trees that provide
styles (Peterson and Johnson 1995). Adaptation responses will
habitat for moose and other large herbivores. On the other
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
759
hand, drier, windy conditions that may coincide with cli-
monly referred to as snow blindness, has always been a
matic warming may cause intense fires which burn off the
problem in the Arctic, as evidenced by Inuit ocular shields.
organic layer and release nutrients from the system (Ka-
Cataract formation has been linked to a variety of causes,
sischke et al. 1995, Starfield and Chapin 1996, Flannigan
including UV radiation. There has been some evidence to
and Van Wagner 1991).
link cortical cataracts with chronic ocular UV-B exposure
(Dolin 1995). Increasing UV-B should be considered a prob-
lem which could be costly for remote health care (IASC
11.6.3.5. Agriculture
1995). Other eye diseases such as spheroidal degeneration of
Arable land in the Arctic is mainly limited by surface and
the cornea and conjunctivea (climatic droplet keratopathy)
soil temperatures. Temperature records from four sites in
and pterygium may or may not be associated with UV-B ex-
Alaska show a general increase in the agricultural growing
posure. However, pterygium mainly occurs under conditions
season between 1924 and 1989 although regional patterns
of climatic extremes and might, therefore, be of special rele-
were inconclusive (Sharratt 1992). Lengthened growing sea-
vance for UV-B in the Arctic (IASC 1995, WHO 1993).
son was due to earlier last spring freezes, later first fall
UV-B radiation is able to suppress the immune system
freezes, or both. These trends are similar to mid-latitude
which may exacerbate a variety of existing health threats.
trends and do not indicate an Arctic amplification of grow-
This immune suppression can cause the reactivation of vi-
ing season length. In a study based on soil surveys and cli-
ruses including herpes, chicken pox, Epstein-Barr, and the
mate in Alaska and northwestern Canada, the impact of a
wart virus. Immunosuppression appears to be independent
doubling of CO2 on arable land was modeled (Mills 1994).
of skin pigmentation, and very small doses of UV-B are able
Potentially arable lands showed increased moisture deficits
to start the reaction (Olivarius et al. 1996). It is unclear how
and an improved climatic capability for agriculture with an
much exposure is necessary to induce a systemic immune
increase of nearly 160 000 km2 (16 M Ha) of arable land in
suppression (IASC 1995).
the study area due to warming temperatures. Moisture limi-
tations, it is predicted, would limit the use of some of this
land, and serious questions remain about the adaptation of
11.7. International efforts
existing plant species to higher CO2 levels (Mills 1994).
11.7.1. Agreements
The Montreal Protocol on Substances That Deplete the
11.6.4. Effects of UV radiation on human health
Ozone Layer and its amendments have set standards to re-
UV radiation is linked to a variety of skin disorders and an
duce the production of CFCs and other ozone depleting sub-
increase in UV dose to northern populations is a health con-
stances. The impetus for these international agreements has
cern. The effects of UV radiation on human health are cov-
been the discovery of ozone holes in Antarctica. Projections
ered more fully in chapter 12, section 12.2.4.2. The health
regarding the Arctic ozone layer are not directly addressed
effects of UV radiation include skin disorders (cancer, changes
by these agreements but, because of the likely link between
in elasticity and hypersensitivity), eye damage, and immune
stratospheric cooling and ozone depletion in the Arctic, fur-
suppression. Skin disorders have been shown to affect differ-
ther investigation is warranted to determine if measures
ent northern populations in different ways. Both carcinomas
need to be taken to assure the protection of the Arctic stra-
and malignant melanomas of the skin are less common in
tospheric ozone layer. Compliance with the Montreal Proto-
the Greenland Inuit population than in the general Danish
col is still of some concern. Bulgaria, Poland, Russia, Ukraine,
population. Several reasons have been posed for this, includ-
and Belarus have each said that they may not be able to
ing the low UV radiation historically received in the Arctic
reach their agreed phase-out goals. Evidence of illegal trade
and the pigmentation of the native people. Changes in elas-
in the controlled substances may undermine the goals of the
tosis of the skin, which can be linked to UV exposure, have
Montreal Protocol and amendments. Continued re-examina-
been observed in Inuit (Wulf et al. 1989). Erythema (sun-
tion of the available science and compliance information is
burn) while a temporary irritant, has also been linked to ma-
necessary to assure the success of the Montreal Protocol's ef-
lignant melanoma. Young children who get severe sunburns
forts to reduce ozone depleting substances.
are particularly prone to skin cancer later in life (WHO
The United Nations convened the Framework
1993). A preliminary investigation has suggested that poly-
Convention on Climate Change at the Rio Earth Summit in
morphic light eruption, a photodermatosis resulting from
1992. 162 countries signed the agreement to implement na-
sun exposure, is more common in the Arctic than at lower
tional policies to monitor and attempt to reduce greenhouse
latitudes. The ratio of UV-B to UV-A has been proposed as
gas emissions. Significant to the Arctic climate, it was also
an explanation for the disorder at high latitudes. Actinic
agreed that sustainable management of greenhouse gas sinks
prurigo, another idiopathic photodermatosis, has been
(natural ecosystems which can remove greenhouse gases from
found to be frequent in the Canadian Inuit population and
the atmosphere) should be promoted. At the more recent
has been linked to UV-B sensitivity (Orr and Birt 1984).
Berlin conference, timeframes to reduce greenhouse gases
Ozone depletion may, therefore, reduce the incidence of
were set, but no new targets were agreed upon. Appropriate
polymorphic light eruption and increase the incidence of
greenhouse targets are critical to the Arctic environment be-
actinic prurigo in the Arctic. Some of these effects are miti-
cause of its high sensitivity to climate change. While re-
gated in the Arctic because most skin is covered by clothing
search to determine the appropriate targets may take many
for much of the year. Changes in personal exposure patterns
years, efforts should be made immediately to assure the
can have a greater effect than small changes in stratospheric
most cautionary levels are agreed upon as soon as possible.
ozone.
The presently proposed system of management depends on
Ocular damage linked to UV exposure includes photo-
individual countries reaching concentration goals within
keratitis, cataracts, and pterygium. The highly reflective
their country limits. This form of regulation may not be suf-
snow covered surfaces in the Arctic can help reflect ambient
ficient to protect the Arctic, which is under no single nation-
UV to the eye, increasing the UV exposure to levels higher
al control. The newly-formed Arctic Council, however, may
than those observed at lower latitudes. Photokeratitis, com-
take up this issue. Further efforts will be needed to assure
760
AMAP Assessment Report
that Arctic levels due to transport do not exceed set stan-
The Nordic Ozone and UV Group has coordinated research
dards. The treaty signed in 1979 at the Geneva Convention
on ozone and UV for the Nordic countries. This group has
concerning long-range transports may be invoked to aid in
been very effective in focusing research needs and intercom-
the control of greenhouse gases in the Arctic. Furthermore,
paring results. Further benefits would be gained from partici-
while the United States and the European Union have agreed
pation from Canada, the United States, and Russia.
that a binding treaty should be drawn up with regard to
The International Arctic Science Committee (IASC), a non-
greenhouse gas emissions, many other countries prefer that
governmental organization established in 1990 to encourage
this agreement remain voluntary.
and facilitate Arctic research, has proposed a comprehensive
program to assess the effects of UV radiation on the Arctic en-
vironment and the regional impacts of climate change in the
11.7.2. Programs
Barents and Bering Seas. The program is presently in search
The Arctic has many unique attributes which make it parti-
of funding to implement the proposed research program.
cularly susceptible to climate change, ozone depletion, and
UV enhancement, more so than mid-latitude and even Ant-
11.7.3. Assessments
arctic environments. While many programs address climate
change at mid-latitudes and ozone in the Antarctic, the in-
This AMAP document is the first document sponsored by a
ternational community has only recently begun to address
large, international committee to assess what is known about
these problems in the Arctic. Individual efforts to under-
climate change, ozone, and UV, and their effects in the Arc-
stand climate change, ozone, and UV radiation in the Arctic
tic. Some of the information presented in this chapter has
are on-going at a number of institutions around the world.
been presented in other assessments. For the most part, how-
Several international programs have been started in the last
ever, the information has not previously been brought to-
decade to address issues of climate change, ozone, and UV
gether in the context of Arctic research. Several important
radiation in the Arctic.
assessments have been written concerning global climate
The EU has been active in climate change issues and has
change, ozone, and UV radiation, yet most effort has been
sponsored a number of projects related to ozone and UV in
placed on northern mid-latitude and Antarctic changes. Con-
the European Arctic. The European Commission's Environ-
siderably less effort has been placed on the Arctic. In some
ment Research Programme has supported European Arctic
cases, the Arctic environment is not addressed at all; in other
Stratospheric Ozone Experiment (EASOE) and Second Eu-
cases, the Arctic environment is addressed as part of the po-
ropean Stratospheric Arctic and Mid-latitude Experiment
lar environments. Such grouping ignores the vast differences
(SESAME) as well as a recent project, Ultraviolet Radiation
between Arctic and Antarctic environments and concerns.
in the Arctic; Past, Present and Future (UVRAPPF) to exam-
ine ozone and UV in northern Europe. The European Com-
11.7.3.1. Climate change
mission has also funded a program of experimental research
into the impacts of enhanced UV-B radiation on European
The Intergovernmental Panel on Climate Change (IPCC),
heathlands (UVECOS), which includes several different eco-
jointly established by the World Meteorological Organi-
systems within the European Arctic from Lapland to High
zation and the United Nations Environmental Programme in
Arctic Svalbard. These efforts have revealed and brought
1988, has produced a number of documents, most notably
into focus many questions which still need to be answered.
four scientific assessments (IPCC 1990a, 1992a, 1994, 1996a)
Because issues of climate change, ozone depletion, and UV
summarizing the present understanding of the science of cli-
radiation affect the entire Arctic, these programs would ben-
mate change, and four assessments of the impacts of climate
efit from expansion or coordination with North American
change (IPCC 1990b, 1992b, 1996b). These assessments
and Russian research communities in order to obtain more
have focused on modeling and model predictions for future
complete information on the Arctic environment.
levels. The IPCC documents have illuminated serious prob-
The World Meteorological Organization (WMO) has
lems in the existing models for Arctic climate. At present no
sponsored and coordinated a number of scientific activities
international programs exist to promote the advancements of
related to climate change, ozone, and UV radiation. The
the climate models for future predictions in the Arctic, al-
Global Atmosphere Watch (GAW) program coordinates
though scientists continue to work on improving their indi-
monitoring sites around the globe, including in the Arctic.
vidual models. The IPCC scientific assessments take a more
The World Climate Research Programme within the WMO
general view and do not focus on any region of the Earth.
has established Stratospheric Processes and their Role in
Because of the unique qualities of the Arctic environment
Climate (SPARC). These programs need to be expanded to
and its interactive processes, many of the general results are
give more emphasis to Arctic issues in line with the impor-
not applicable to the Arctic. Focused effort, on the part of
tance of the Arctic in the global climate system. The World
the IPCC, to examine the Arctic's responsivity to climate
Climate Research Programme has also established the Arctic
change through available data from the Arctic would be ap-
Climate System Study (ACSYS) to examine freshwater bal-
propriate and useful to understanding global climate change.
ance, runoff, and sea ice in the Arctic. A useful product
which may result from this program is the ACSYS precipi-
11.7.3.2. Ozone and UV
tation data center to be established in Germany.
Toronto hosts the WMO's Ozone and UV Database cen-
The World Meteorological Organization, in conjunction
ter which offers data over the Internet. There is increased
with the United Nations Environmental Program (UNEP),
need to include more ozone and UV data from the Arctic in
the US National Oceanic and Atmospheric Administration
this center. The responsibility for inputting ozone and UV
(NOAA), and the US National Aeronautic and Space Agency
data lies with the individual countries and agencies collect-
(NASA), has produced several assessments addressing the
ing the data. The data, once available, need to be examined
present understanding of ozone depletion. The most recent
in a regional, rather than national, perspective in order to
report, Ozone Depletion: 1994 (WMO 1994), documents
understand observations with respect to the Arctic. This is
observed ozone loss in the Arctic which is consistent with
beyond the present scope of the WMO data center.
photochemical model calculations. However, the recent
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
761
11.8.2. Climate change: Recommendations
ozone anomalies, which had not been well documented
when the last report was written, need to be addressed in
There is a strong need to improve understanding of the
future documents. The Arctic has been grouped together
climate system and to develop reliable methods of climate
with the Antarctic in past reports. In light of recent under-
prediction for the Arctic. Baseline information is needed
standing of the different character of ozone in the Arctic
throughout the Arctic to be able to assess any future changes.
versus the Antarctic, future assessments should address the
Ice and lake sediment cores, peat cores, biological records,
Arctic separately, with full attention to what is known about
archaeological records, and historical documents should be
the Arctic and the observed anomalies. Future assessments
examined to determine the climate of the past few hundred
should also address the issue of UV radiation in the Arctic
years for the Arctic. Traditional knowledge needs to be doc-
in more depth than previous reports.
umented and incorporated into the present scientific knowl-
UNEP has co-sponsored several important reports on UV
edge of climate change. Crucial aspects of climate in the
radiation and its effects. However, very little attention has
Arctic, particularly the hydrological and trace gas cycles,
been given to the Arctic environment in any of these reports.
are insufficiently understood. Increased knowledge of these
The Scientific Committee on Problems of the Environment
systems is necessary before reliable predictions can estimate
(SCOPE) has also sponsored several important reports on
future changes. The role of gaseous exchange in Arctic ter-
UV radiation, again with no significant attention to the Arc-
restrial areas requires further investigation to understand
tic. The effects of UV radiation in the Arctic were reviewed
both the Arctic climate and the global climate. Existing at-
by the International Arctic Science Committee (IASC). The
mospheric models need to better incorporate the dynamical
resulting reports offer an extensive evaluation of what is
nature of the Arctic feedback mechanisms to provide valid
known about UV effects in the Arctic and underlines how
estimates.
little is known about the effects of UV on Arctic species,
Every effort should be made to increase the number of
ecosystems, and human inhabitants (IASC 1995, 1996).
climatologically useful observations on, above, and below
the ice pack, with a concentration of effort in critical regions
that are particularly sensitive to climate change, such as
11.8. Conclusions and recommendations
shelf regions and the Arctic Ocean's primary outflow region,
Fram Strait. Buoys, moorings, aerial surveys, and satellite re-
11.8.1. Climate change: Conclusions
mote sensing are likely sources of the information needed to
The climate of the Arctic affects both the inhabitants of the
monitor the state of the Arctic ice pack. Increased support of
Arctic and the global climate system. Anthropogenically-dri-
such measurement programs is important to understanding
ven climate change is likely to be most severe in the Arctic
changes in Arctic climate.
because of the strong feedback mechanisms. The Arctic has
undergone rapid changes in the past. Recent changes have
11.8.3. Ozone: Conclusions
been linked to anthropogenic forcing; but despite the global
consequence of changes in the Arctic climate, monitoring of
In the last 20 years, ozone concentrations in the Arctic have
basic climatic parameters, such as sea ice, precipitation, and
been changing more than those at mid-latitudes, with ob-
the atmosphere, are not adequate to assess these recent
served trends of in excess of 10% per decade. Of more con-
changes. Present monitoring in the Arctic is not adequate to
cern than the average trend is the occurrence of short-term
assess the impacts of global climate change. The uneven geo-
episodes of extreme ozone depletion. There are indications
graphical location of present monitoring stations limits the
that the occurrence of these episodes is increasing, yet their
present ability to understand the climate system.
full cause is not well understood. Because ozone depletion in
In preparing this document it became evident that knowl-
the Arctic is linked to stratospheric cooling, future climate
edge from Arctic people is underutilized in climate change
change is expected to have a strong influence on future ozone
research. Arctic peoples have passed down information
levels. The reductions of CFC's alone may not be enough to
through generations on climate change which has been use-
restore the Arctic ozone layer to pre-1980s levels.
ful for their survival. Traditional knowledge is a valuable
source of information on present climate dynamics and
11.8.4. Ozone: Recommendations
needs to be documented and included in future assessments.
Changes in sea ice coverage and thickness are the primary
The recent changes in the ozone concentrations in the Arctic
driving forces in the polar amplification of global warming
require further examination. Both the mean trends and dis-
forecast by many climate models. Yet there are few continu-
tributions in the Arctic ozone layer need to be understood
ous and ongoing measurements of the surface energy bal-
before confidence may be placed on predictions about the
ance, of the ice thickness distribution, or of the structure of
Arctic ozone layer. There is a pressing need to accurately ex-
the upper ocean. In the past, the drifting ice stations of the
plain the mechanisms responsible for the recently documented
Former Soviet Union provided many key measurements, but
ozone anomalies in the Arctic. The cause and impact of
that series of manned camps has ended and none from any
these anomalies need to be further understood. The poten-
nation are likely to replace them.
tial link between climate change, in particular the cooling of
Prediction of Arctic climate is not reliable at this time.
the stratosphere, and Arctic ozone concentrations requires
The complex interactions of the various components of the
immediate further research.
Arctic make climate modeling and therefore climate predic-
tions extremely difficult and uncertain at this time. The cli-
11.8.5. UV: Conclusions
mate models in existence do not agree well with current
measurements, nor do they agree with each other with re-
UV radiation in the Arctic is not negligible, as is often as-
spect to predictions when applied to the Arctic. Sea ice dy-
sumed, because of the large amount of diffuse radiation.
namics and trace gas balance, particularly over land, are
In the Arctic, UV is difficult to measure and difficult to esti-
very important aspects of the climate system in the Arctic,
mate from satellite information, yet existing UV ground-
yet very little is known about changes taking place in either
monitoring stations in the Arctic are very unevenly distri-
of these components.
buted, so that the present spatial coverage of UV monitoring
762
AMAP Assessment Report
is insufficient. The increase of UV during the observed ozone
11.8.9. Climate change and UV effects
depletion events needs further study, particularly because
on humans: Conclusions
these events often occur in spring-time when snow cover is
decreasing and ecosystems are extremely sensitive.
The effects of climatic warming on the Arctic ecosystems are
likely to be large and to have a noticeable impact on present
human ways of life. Climate change, through its effect on
11.8.6. UV: Recommendations
physical properties of the land and ocean, could greatly im-
The existing UV monitoring efforts in the Arctic need to be
pact infrastructure, especially transportation and large struc-
expanded to give more broad geographical coverage; moni-
tures; this could make the Arctic more accessible to develop-
toring is particularly needed in the Russian Arctic. Merging
ment. Agriculture, forestry, and fisheries will likely be altered.
the available UV data with satellite information to develop
While these changes may include some economic benefits,
models for estimating UV throughout the entire Arctic is
they are likely to permanently impact traditional ways of life.
necessary for determining a broad UV climatology of the
Sea level rise could displace many permanent communities.
Arctic. Both the UV reaching vertical surfaces and that
Effects of UV radiation on human health in the Arctic are
reaching horizontal surfaces are relevant to the ecosystems
larger than previously suspected. The strong seasonal cycle
in the Arctic, and more research is needed to determine the
often exposes populations to high UV levels in the early
character and climatology of ambient UV levels. UV during
spring when they have not yet developed protective pigmen-
episodes of severe ozone depletion events needs to be under-
tation. UV has been linked to dermatological, ocular, and
stood further.
immunosuppression effects, all of which can have severe im-
pacts on the health of Arctic people. The low sun angle and
high reflectivity of snow make UV even more hazardous for
11.8.7. Climate change and UV effects
Arctic populations than previously thought. Because of the
on ecosystems: Conclusions
high cost of administering health care in the Arctic, UV ef-
Despite the general understanding of possible climate changes
fects due to decreasing ozone are likely to have high eco-
to the Arctic, little is known about the specific effects of cli-
nomic impact.
mate change on marine or terrestrial ecosystems or on indi-
vidual species. Little is known about widespread effects of
11.8.10. Climate change and UV effects
climate change which have occurred already because of the
on humans: Recommendations
lack of ecosystem monitoring and the complexity of the
feedback mechanisms in the Arctic. Changes in sea ice,
Of particular importance is an examination of the effects of
snow, and permafrost extent will determine the available
UV and climate change on Arctic peoples and on the plants,
habitat for plants and animals in the Arctic. Climate changes
mammals, and fish they harvest for food, on grazing animals,
are likely to take place faster than Arctic ecosystems are
and on the physical environment. It is important to include
likely to be able to respond.
indigenous people in future policy planning and research ef-
The effects of UV radiation on Arctic ecosystems are
forts in order to understand the impacts of both UV and cli-
not well understood. Many of the assumptions made for
mate change on traditional ways of life.
the Arctic are based on UV studies carried out in the Ant-
The examination of the direct effect of UV radiation on
arctic or at mid-latitudes. Those UV effects that have been
human health requires immediate attention, particularly
observed appear to be tied to such factors as water stress
with respect to ocular damage and additionally to immuno-
and other environmental factors that are also influenced
supression effects and dermatological disorders.
by climate change. The springtime changes in ozone con-
centrations could expose primary production in the Arctic
Ocean as well as the terrestrial ecosystems to harmful UV
Acknowledgments
radiation because of the timing and intensity of the changes;
changes in primary production would impact higher trophic
Editors
levels.
Elizabeth C. Weatherhead, C. Michele Morseth.
Authors
11.8.8. Climate change and UV effects
R.B. Alley, A.L. Andrady, S.E. Bayley, H. Beach, L.O. Björn,
on ecosystems: Recommendations
J-P. Blanchet, N. Bond, R. Booth, D. Bromwich, T. Calla-
ghan, E. Carmack, B. Chen, J. Christy, V. Collin-Wilmsen,
Climate change effects on ecosystems need to be examined
S. Das, M.S.V. Douglas, P. Gleckler, P. Groisman, W. Gra-
in terms of an integrated assessment, taking into account
néli, O.W. Heal, H. Hengeveld, D.O. Hessen, H.P. Hunting-
relevant environmental factors such as acidification, UV
ton, M.O. Jeffries, K. Jokela, T.R. Karl, J. Key, K. Kvenvol-
and pollutants, as well as the effects of climate change on
den, M. Lange, R. Lindsay, J. Maslanik, A. McCulloch, T. Mc-
competing species within an ecosystem. The potential for
Govern, I. Melnikova, P. Novelli, A. Ogilvie, S. Oltmans,
climate change to alter the Arctic environment demands
B.R. Parker, D. Perovich, B.J. Peterson, W. Pollard, B.B. Pré-
immediate assessment of available baseline information as
zelin, C.E. Randall, D.A. Robinson, D. Schindler, A.J. Schwei-
well as fundamental research into the effects of change on
ger, J-S. Selmer, M. Serreze, P. Sheridan, D. Sliney, J.P. Smol,
particular species as well as ecosystems. UV effects need to
K. Stamnes, P. Taalas, P. Tans, W.B. Tucker III, C.J. Voro-
be examined in terms of an integrated assessment, taking
smarty, R.Weaver, A.P. Wolfe, M-K. Woo, H.C. Wulf, S-Å.
into account relevant environmental factors, such as acidi-
Wangberg.
fication and water stress, as well as the effects of UV on
competing species within an ecosystem. Both aquatic and
Reviewers
terrestrial ecosystems need to be examined through efforts
R.G. Barry, J.D.W. Kahl, M. Lange, M. Meier, B.B. Prézelin,
such as IASC's proposal to establish and coordinate focused
F. Roots, D. Schindler, J-S. Selmer, G. Weller.
centers of research in the Arctic for the purpose of studying
UV effects.
Chapter 11 · Climate Change, Ozone, and Ultraviolet Radiation
763
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Document Outline
- Go to opening screen
- 11.1. Introduction
- 11.2. Climate change
- 11.2.1. Dynamic interactions
- 11.2.2. Climate change: Methods of assessment and recent trends
- 11.2.3. Ability to predict
- 11.2.4. Components of the Arctic
- 11.3. Arctic stratospheric ozone
- 11.3.1. Arctic stratospheric ozone
- 11.3.2. Chemistry of ozone depletion … Polar vortex dynamics
- 11.3.3. Measurements of stratospheric ozone
- 11.3.4. Results of measurements
- 11.3.5. Arctic ozone anomalies
- 11.4. UV radiation
- 11.4.1. Measurements
- 11.4.2. Modeling
- 11.4.3. Biologically relevant UV
- 11.4.4. UV on land
- 11.4.5. UV penetration in aquatic systems
- 11.5. Effects of climate change and UV radiation on the biosphere
- 11.5.1. Terrestrial ecosystems
- 11.5.2. Aquatic ecosystems
- 11.6. Effects of climate change and UV radiation on Arctic peoples
- 11.6.1. Prehistorical and historical effects of climate change
- 11.6.2. Settlement and resource use
- 11.6.3. Economic activities
- 11.6.4. Effects of UV radiation on human health
- 11.7. International efforts
- 11.7.1. Agreements
- 11.7.2. Programs
- 11.7.3. Assessments
- 11.8. Conclusions and recommendations
- 11.8.1. Climate change: Conclusions
- 11.8.2. Climate change: Recommendations
- 11.8.3. Ozone: Conclusions
- 11.8.4. Ozone: Recommendations
- 11.8.5. UV: Conclusions
- 11.8.6. UV: Recommendations
- 11.8.7. Climate change and UV effects on ecosystems: Conclusions
- 11.8.8. Climate change and UV effects on ecosystems: Recommendations
- 11.8.9. Climate change and UV effects on humans: Conclusions
- 11.8.10. Climate change and UV effects on humans: Recommendations
- Acknowledgments
- References