This is Chapter 6 of the Arctic Climate Impact Assessment.
Lead Author: John E.Walsh; Contributing Authors: Oleg Anisimov, Jon Ove M. Hagen,Thor Jakobsson, Johannes Oerlemans,Terry D. Prowse,Vladimir Romanovsky, Nina Savelieva,Mark Serreze, Alex Shiklomanov, Igor Shiklomanov, Steven Solomon; Consulting Authors: Anthony Arendt, David Atkinson, Michael N. Demuth, Julian Dowdeswell, Mark Dyurgerov, Andrey Glazovsky, Roy M. Koerner, Mark Meier, Niels Reeh, Oddur Sigur0sson, Konrad Steffen, Martin Truffer
Recent observational data present a generally consistent picture of cryospheric change shaped by patterns of recent warming and variations in the atmospheric circulation. Sea-ice coverage has decreased by 5 to 10% during the past few decades.The decrease is greater in the summer; new period-of-record minima for this season were observed several times in the 1990s and early 2000s. The coverage of multi-year ice has also decreased, as has the thickness of sea ice in the central Arctic. Snowcovered area has diminished by several percent since the early 1970s over both North America and Eurasia. River discharge over much of the Arctic has increased during the past several decades, and on many rivers the spring discharge pulse is occurring earlier.The increase in discharge is consistent with an irregular increase in precipitation over northern land areas. Permafrost temperatures over most of the subarctic land areas have increased by several tenths of a degree to as much as 2 to 3 ºC during the past few decades. Glaciers throughout much of the Northern Hemisphere have lost mass over the past several decades, as have coastal regions of the Greenland Ice Sheet.The glacier retreat has been especially large in Alaska since the mid-1990s. During the past decade, glacier melting resulted in an estimated sea-level increase of 0.15 to 0.30 mm/yr. Earlier breakup and later freeze-up have combined to lengthen the ice-free season of rivers and lakes by up to three weeks since the early 1900s throughout much of the Arctic.The lengthening of the ice-free season has been greatest in the western and central portions of the northern continents.While the various cryospheric and atmospheric changes are consistent in an aggregate sense and are quite large in some cases, it is likely that low-frequency variations in the atmosphere and ocean have played at least some role in forcing the cryospheric and hydrological trends of the past few decades.
Model projections of climate change indicate a continuation of recent trends throughout the 21st century, although the rates of the projected changes vary widely among the models. For example, arctic river discharge is likely to increase by an additional 5 to 25% by the late 21st century.Trends toward earlier breakup and later freeze-up of arctic rivers and lakes are likely if the projected warming occurs. Models project that the wastage of arctic glaciers and the Greenland Ice Sheet will contribute several centimeters to global sea-level rise by 2100.The effects of thermal expansion and isostatic rebound are superimposed on the glacial contributions to sea-level change, all of which combine to produce a spatially variable pattern of projected sea-level rise of several tens of centimeters in some areas (the Beaufort Sea and much of the Siberian coast) and sea-level decrease in other areas (e.g., Hudson Bay and Novaya Zemlya). Increased inflow of cold, fresh water to the Arctic Ocean has the potential for significant impacts on the thermohaline circulation and global climate.
Models project that summer sea ice will decrease by more than 50% over the 21st century, which would extend the navigation season in the Northern Sea Route by between two and four months. Snow cover is projected to continue to decrease, with the greatest decreases projected for spring and autumn. Over the 21st century, permafrost degradation is likely to occur over 10 to 20% of the present permafrost area, and the southern limit of permafrost is likely to move northward by several hundred kilometers. Arctic coastal erosion and coastal permafrost degradation are likely to accelerate this century in response to a combination of arctic warming, sea-level rise, and sea-ice retreat.
Chapter 6: Cryosphere and Hydrology
6.2. Precipitation and evapotranspiration
6.3. Sea ice
6.4. Snow cover
6.5. Glaciers and ice sheets
6.7. River and lake ice
6.8. Freshwater discharge
6.9. Sea-level rise and coastal stability