Record year for Greenland ice sheet melt
By Koren Capozza
UPI Science News
From the Science & Technology Desk
Published 12/7/2002 11:59 PM
SAN FRANCISCO, Dec. 7 (UPI) — New studies on atmospheric, marine and terrestrial changes at the planet’s poles suggest Earth may be entering a period of rapid climatic change.
Scientists caution that the evidence is mixed and the jury still out on whether humans are causing the present period of global warming, but significant new findings add credence to the theory that the planet is experiencing an unprecedented rate of system change.
One piece of evidence comes from a University of Colorado study, which found that the Greenland ice sheet melted in record amounts during 2002 while the Arctic sea ice plummeted to the lowest level in satellite record.
Satellite data collected since 1979 indicate a dramatically increasing melting trend, with the 2002 melt extent surpassing all previous records. Authors of the study suspect the 2002 sea ice record may actually be the lowest in several centuries.
Run-off from the melting ice is also likely contributing to a rise in ocean levels and a decrease in sea ice, said the authors.
“We warm up the [sea] ice — more of it melts. That opens more water and more radiation is absorbed which continues the vicious cycle,” said James Morison, professor of marine science at the University of Washington.
As the surface of the Greenland ice cap melts, it may also set in motion a cycle which accelerates the rate of ice flow. Melt water penetrates the ice sheet up to 2 km deep creating a lubricating thin layer of water which causes the ice sheet to slide towards the ocean, said Konrad Steffen, professor of geography at the University of Colorado at Boulder.
Current temperatures in Greenland seem to mirror another period of abnormal warming which occurred in the 1930s. However, the rate of temperature increase is much higher than in the past, said Steffen.
A different cycle with similar consequences is occurring at the tree line in Arctic regions, according to research by scientists at the University of Alaska at Fairbanks (UAF). The tree line is creeping forward, encroaching on regions which were previously inhospitable to forest growth. Researchers have also observed an increase in spruce forest density and an expansion of shrubs in the treeless portion of the Arctic.
Aerial photographs taken of an Arctic region in Alaska in 1949 compared with snapshots taken of the same region in 2000 demonstrate that the area, once mostly denuded of vegetation, is now peppered with shrub vegetation.
This rapid increase in plant growth in the Arctic may influence the climate system, said F. Stuart Chapin of UAF. The shrubs and trees absorb more of the sun’s energy, which is later transferred to the atmosphere — a process that may enhance the Arctic warming effect. However, because plants also mitigate the influence of increased carbon dioxide in the atmosphere, it’s unclear what net effect this new plant growth will ultimately have on the global environment, noted Chapin.
Still, Chapin estimates that if this expansion in vegetation growth occurred throughout the Alaskan arctic, it could increase summer temperatures in the northern part of the state by as much as 2.5 to 7 degrees F.
“If we look at these individual pieces of evidence, it’s hard to conclude that there’s rapid change going on but taken together it represents a pretty compelling story that change is occurring,” said Larry Hinzman, researcher with the Water and Environmental Research Center at UAF.”
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Posted by: Paul on December 08, 2002 at 19:11:24