Global mean temperatures have risen one degree Fahrenheit over the past 100 years, with more than half of the increase occurring in the last 25 years, according to University of Colorado at Boulder Senior Researcher Richard Armstrong.
"As slight as that may seem, it’s enough to make a difference," said Armstrong, who is affiliated with the National Snow and Ice Data Center headquartered at CU-Boulder. "Now, long-term monitoring of a series of cold region, or cryospheric, parameters shows that for several decades the amounts of snow and ice around the world have been decreasing."
To assemble the big picture, the NSIDC, commemorating 25 years of service, has organized a special session at the 2001 Fall Meeting of AGU, "Monitoring an Evolving Cryosphere." The session begins Tuesday, Dec. 11, and extends through Thursday afternoon, with 75 contributions from all areas of cryospheric study. Papers and posters include examinations of lake and river ice, glacier dynamics and mass ice balance studies in polar and continental glaciers, regional and polar snow cover trends and variations of Canadian ice cap elevation changes.
In the world of climate change, trends are most readily observed in the Earth’s cold regions, where the sensitivity of ice and snow to temperature changes serves as an early indicator of even relatively small differences, he said. Today’s receding and thinning sea ice, mountain glacier mass losses, decreasing snow extent, melting permafrost and rising sea level are all consistent with warming.
Although Arctic sea ice extent is decreasing by about 3 percent per decade, the trends are not uniform. While recent studies have indicated that the ice thickness also had decreased over several decades, new information shows that the ice may have thinned rapidly, Armstrong said.
Examination of springtime ice thickness in the Arctic Ocean indicates that the mean ice thickness decreased 1.5 meters between the mid-1980s and early 1990s.
"We attribute at least some of the thinning to changes in Arctic atmosphere and ice circulation patterns. While no similar trend was evident in ice thickness near the North Pole, the data unquestionably indicate a decrease in total ice volume in the western Arctic Ocean," said Walter B. Tucker, of the Army Cold Regions Research and Engineering Laboratory in Hanover, N.H.
"At low latitudes, glacial changes are pronounced, uncontested and solid evidence of climate warming," said Eric Rignot, a researcher at the Radar Science and Engineering Section of NASA’s Jet Propulsion Laboratory. "But what is happening in the polar ice sheets is less clear.
Materials provided by University Of Colorado At Boulder. Note: Content may be edited for style and length.
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