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What is the evidence for
Arctic sea-ice thinning? Is Arctic sea-ice thinning everywhere or in
specific regions or areas? How substantial is the sea-ice thinning?
Is there evidence of changes in the aerial distribution of Arctic sea-ice?
Is Arctic sea-ice now forming later in the season and melting earlier?
What are the likely causes of the observed changes in Arctic sea-ice?
What are the long and the short-term implications of Arctic sea-ice
thinning in terms of climate change and in terms of possible impacts
on humans and ecosystems? Have Alaskan Native Peoples, in particular,
observed similar changes, and if so, what has been the impact of these
and other changes?
INTRODUCTION:
Charles (Chip) Groat
Director, U.S. Geological Survey, U.S. Department of the Interior, Reston,
VA
SPEAKER:
Douglas G. Martinson
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY
SPEAKER:
Caleb Pungowiyi
Director, Natural Resources Program, Eskimo Walrus Commission, Nome,
AK
OVERVIEW
Sea-ice has covered the
majority of the Arctic Ocean, year-round, with a 9-foot thick blanket
of ice as expansive as the United States, for as long as civilization
can recall. In sunlight, this vast area is blindingly radiant; a reflective
surface remarkably efficient in reflecting sunlight back into space,
before the sun's rays can heat the region. Likewise, the presence of
sea-ice serves to insulate the frigid atmosphere from the relatively
warm ocean water (which cannot be colder than the freezing point) thus
preventing the ocean from significantly warming the atmosphere. Sea-ice
is such an efficient insulator that in its absence, the exposed ocean
water would warm the overlying air, in winter, by some 20 to 40 degrees
C. Moreover, the exposed ocean is nearly as impressive in its ability
to absorb the warming sunlight as the ice is in reflecting it back into
space. Consequently, the presence or absence of ice leads to considerable
differences in the temperature (and with that, circulation) of the overlying
atmosphere. This dramatic contrast makes polar climate highly sensitive
to changes in sea-ice - even small changes in the sea-ice can result
in large changes in the polar climate. On a grander scale, these same
characteristics that constrain the polar temperatures help define the
temperature contrast between the tropics and the poles. Climate can
be thought of as the Earth's attempt to eliminate this contrast, that
is, to redistribute excess heat received in the tropics to the heat-starved
Polar Regions. In the simplest sense, the vigor, and many other characteristics
of climate, are controlled by the magnitude of this temperature contrast.
Thus, anything that influences polar temperatures can influence global
climate as well.
Observations are beginning
to document and reveal just how changes in the Arctic climate influence
the climate outside of the Polar Regions. Global climate model simulations,
on the other hand, provide additional insights into how the Earth's
climate might change as a result of specific changes in extent, thickness,
and duration of sea-ice. These models also provide insights as to how
the sea-ice may change as global climate changes, thus presenting clues
as to how to interpret observed changes in sea-ice.
Instrumental and Observational
Records of Changes in Arctic Sea-Ice
Though scientists have
been aware of the potential sensitivity of the climate system to changes
in sea-ice cover for many years, it has only been since the early 1970s
that scientists have finally been able to regularly observe sea-ice
through constant monitoring via satellites. During this interval of
time, scientists have observed a clear and steady decline in the extent
of the Arctic sea-ice cover, showing it to be disappearing at a rate
of approximately 3% each decade. There have also been a number of exceptionally
abnormal years recently, even in light of this steady decline. For example,
this decade has witnessed four summers in which the aerial extent of
Arctic sea-ice was the smallest ever observed. Furthermore, other, less
complete records of Arctic sea-ice suggest that the decline in extent
has been continuous since mid-century. While the reduction in ice extent
is unequivocal, changes in thickness are also apparent, but more ambiguous.
Last year, during a year-long experiment in the Arctic, the thickest
ice floe found for the purposes of setting up an ice station, was only
60% of the average (not even maximum) sea-ice thickness anticipated.
Measurements in the upper
Arctic Ocean also indicated an excess of freshwater (largely confined
to regions of thin ice), which was consistent with the notion of excess
melting during the previous year. Likewise, recently documented changes
in other parts of the Arctic Ocean are strongly suggestive (indirectly)
of a more pervasive thinning of Arctic sea-ice. The changes serve to
introduce considerable heat from the ocean to the ice. Such changes
imply that winter sea-ice growth will be reduced by 70-80% in those
regions in which these and other changes have occurred. On the other
hand, recent results from submarine surveys under the ice do not reveal
any clear indication of a general basin-wide thinning. While differences
in these observations are yet to be reconciled, the steady decline in
the aerial extent of sea-ice cover, predominantly in summer, suggests
a steady decline in the volume of sea-ice and a decline in the amount
of freshwater locked up in sea-ice.
The causes for the observed
sea-ice changes are still uncertain, though there are some likely candidates,
such as the global warming that has been documented over the majority
of this century. Relative to mean global temperatures, temperatures
in the Polar Regions show the same general trends, but are amplified
relative to the changes observed in the tropics. Therefore, a general
climate warming of a degree or two at lower latitudes, is equivalent
to a warming of several degrees at the poles. The changes in Arctic
sea-ice do indeed track changes in polar temperature, but whether increased
temperature is a cause or an effect of the sea-ice change is unclear.
The sea-ice changes are also remarkably consistent with model predictions
given increases in atmospheric carbon dioxide. On the other hand, changes
in sea-ice also accompany changes in the regional atmosphere and as
such, may or may not be related to a global warming. In fact, some of
the above changes have been attributed to El Nino/La Nina cycles. These
atmospheric changes can modify the sea-ice by altering the upper ocean
structure and the winds, both of which influence ice growth, melt and
drift. Whether the changes in the atmosphere are responding to the change
in sea-ice or vice versa is not currently known. Confounding the interpretations
further is the fact that all of the various changes are generally consistent
with the global warming trends. At present, despite considerable uncertainties,
global warming seems to be the most likely candidate driving the changes
(and the one most consistent with the disparate observational evidence
and modeling studies).
While there is some indication
of what might be driving the observed changes, the most compelling unanswered
question at this time is whether these changes are part of a long-term
climate trend, or part of a climate cycle. In the latter instance, one
would expect to see a future reversal in the observed changes. However,
at present there is evidence that may support both possibilities, in
which case the most likely future projection would involve a long term
decline in the Arctic sea-ice cover, tempered in some years by a cooling
(ice build-up) phase of the cycle, and enhanced in other years by coinciding
with the warming (melting) phase of the cycle. If the decline in Arctic
sea-ice cover does continue at the present rate, the year-round (perennial)
ice will eventually disappear and ice will only appear in winter.
Impacts of Changes in
Arctic Sea-Ice: A Native Alaskan Perspective
The Bering Sea and the
Arctic Ocean sea-ice are important supporters and providers of life
to the indigenous people whose lives depend on the resources from these
very productive seas. For those who live in the Arctic regions, climate
change has had, and will have, serious consequences. While the scientific
community studies climate change and tries to determine whether the
observed changes are part of a long-term global climate warming trend,
many of the indigenous peoples of the Arctic are already feeling some
of the impacts of a changing, warming climate. It is important to understand
that from the perspective of many indigenous peoples who live in the
Arctic region, even small changes in the climate or environment can
have dramatic impacts on the lives of those whose livelihood is often
directly dependent upon, and tied to natural resources and the functioning
of ecosystems.
The Yupik and other indigenous
peoples of the Arctic have observed and experienced the following changes
which have had the following impacts:
- A reduction in sea-ice
and changes in the timing of ice formation and thaw in the Bering
and Chukchi Seas.
Impact - When
sea-ice is late in forming certain forms of hunting are delayed
or may not take place at all. When sea-ice in the spring melts or
deteriorates too rapidly, it greatly decreases the length of the
hunting season for all communities. In both, the spring and the
fall hunting season, the window of opportunity is very limited and
is also affected by others environmental conditions such as changes
in wind, precipitation, and surf. The fall of 1997 and 1998 were
two of the warmest in recent years, especially 1998. In both years
hunters reported poor seal hunting.
Impact - Different
species of fish have historically followed or accompanied the freeze-up
of sea-ice. In the fall of 1998, freeze-up did not occur until late
November. Up until that time, no fish or seals were caught in any
abundance.
- Changes in precipitation
in the summer, fall, and winter.
Impact - Many
traditional foods are dried (e.g., seal, walrus, whale, fish, and
birds) in the spring and summer in order to preserve them for consumption
over the long winter months. When the air is too damp and wet during
the "drying" seasons, food that is set out for drying gets moldy
and sour. The Yupik and other indigenous communities have observed
the prevalence of more rain, fog, and cloudy skies during the "drying"
seasons.
Impact - The
length of the wet season also affects the ability to gather greens
such as willow leaves, beach greens, sour dock, wild celery, stink
weeds, Labrador tea, etc., The Yupik and other indigenous peoples
have been experiencing wetter, earlier springs, and wetter, earlier
falls which affect the drying and gathering of traditional plants.
- Changes in storm surges,
shore erosion, and wind.
- Changes in migration
patterns and habitat of terrestrial and marine mammals.
- Changes in the availability
of food resources for sea birds and marine life.
Impact - Each
species of marine mammals requires a certain type of sea-ice for
resting, molting, socializing, breeding, rearing, and migration.
As marine mammal hunters, the Yupik and other indigenous peoples
of the Arctic closely observe the quality of ice for spring hunting.
If it has been a mild fall and winter, ice quality is poor. In this
case the ice is soft, thin, and disintegrates easily from wind,
waves, and warm temperatures. As a result, some of the newborn seal
and walrus pups do not have sufficient time to wean properly and
typically, will not survive. In June of 1996 many seal pups washed
up dead on the shores of St. Lawrence island. Few walrus calves
were reported in 1997 and 1998 as well. In addition, the lack of
ice or poor ice conditions will result in stress on marine mammals
and affect productivity.
Biography of Caleb
Pungowiyi
Caleb Pungowiyi is
the current Director of the Natural Resources Program of the Subsistence
and Eskimo Walrus Commission. He also serves as Commissioner on the
Bering Straits Regional Commission and as an active Member on the following
Boards and Commissions: Marine Mammal Commission; Advisory Committee
of the Office of Polar Programs of the National Science Foundation;
Alaska Scientific Review Group; Rural Alaska Resources Association;
Bering Sea Impact Study; and the Indigenous Peoples Council for Marine
Mammals.
Mr. Pungowiyi is the former
President and CEO of the Inuit Circumpolar Conference, representing
120,000 Inuit of Alaska, Canada, Greenland and Chukotka, Russia. In
addition, he has served as a Member of the following Boards and Commissions:
Alaska Native Science Commission; the National Academy of Sciences Polar
Research Board's Committee on Bering Sea Ecosystems; Advisory Panel
on Arctic Impacts from Soviet Nuclear Contamination, with the former
Congressional Office of Science and Technology; Native American Rights
Fund; Alaska Coastal Policy Council; and the Alaska Conservation Foundation.
Biography of Douglas
Martinson
Douglas Martinson
is a senior research scientist at the Lamont-Doherty Earth Observatory,
and an Adjunct Professor in the Department of Earth and Environmental
Sciences at Columbia University. His primary research interest is directed
at understanding how changes in Polar Regions affect the global climate.
His research also involves both modeling and field work. In this capacity
Dr. Martinson has been to the Arctic and Antarctic polar oceans many
times, and was awarded the United States Antarctic Service Medal in
1987. He was Chief Scientist for the first sea-ice camp in the Antarctic
region (Ice Station Weddell, 1992), Chief Scientist on the inaugural
science cruise of the first U.S. Ice-Breaking Research Vessel (the Nathaniel
B. Palmer), and a member of the Science Steering Committee and a Principal
Investigator for the recently concluded NSF (National Science Foundation/Office
of Naval Research SHEBA (Surface Heat Budget of the Arctic) project,
which operated from a field camp situated in the Arctic for an entire
year. Dr. Martinson is presently preparing for his next field trip to
study the Antarctic winter, which will be underway in a couple of months.
He is author of dozens of articles in the peer-reviewed literature,
the latest one dealing with the future of the Arctic Sea-Ice Cover.
Dr. Martinson also teaches a graduate course on "quantitative methods
of data analysis". Dr. Martinson is a member of a number of national
and international committees dealing with global climate change, and
the role of Polar Regions in climate. He was Chairman of the National
Research Council's (NRC's) Panel on Climate Variability over Decade
to Century Time Scales which recently produced the U.S. Science Strategy
for Studying Climate Variability over Decade-to-Century Time Scales.
He is a member of the NRC Global Change Research Committee, and NRC
Climate Research Committee. He is a member of the Science Steering Group
for the World Climate Research Programme's (WCRP's) Climate Variability
and Prediction (CLIVAR) project, the Science Steering Group for the
WCRP Arctic Climate System (ACSYS) project, and a member of the WCRP
Task Force defining the new Climate and Cryosphere project, among others.
He has also served on a number of advisory committees (as Chair or as
a member) at the following institutions and agencies: the National Science
Foundation, the National Aeronautics and Space Administration, and the
American Meteorological Society.
Dr. Martinson received
his Ph.D. at Columbia University, NY, in 1982 in paleoclimatology and
polar oceanography. He was later awarded a Post-Doctoral Fellowship
in the Department of Physical Oceanography at the Woods Hole Oceanographic
Institution, where he stayed until returning to Lamont-Doherty and Columbia
University in 1985.
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