Arctic Sea-Ice: Changes, Causes, and Implications
U.S.Global Change Research Program -- April, 1999
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 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. Asa 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.
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.
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. 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.