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2/13/2007

Glaciers not on simple, upward trend of melting

Earth News: Greenland
Global Warming Alert
Photo: File photo of a glacier in Greenland. Getting accurate computer models of Greenland and Antarctic glaciers is important because 99 percent of the Earth's glacial ice is found in those two places. Glacial ice is second only to the oceans as the largest reservoir of water on the planet.

Feb 12, 2007
Two of Greenland's largest glaciers shrank dramatically and dumped twice as much ice into the sea during a period of less than a year between 2004 and 2005. And then, less than two years later, they returned to near their previous rates of discharge.
The variability over such a short time, reported online Feb. 9 on Science magazine's Science Express, underlines the problem in assuming that glacial melting and sea level rise will necessarily occur at a steady upward trajectory, according to lead author Ian Howat, a post-doctoral researcher with the University of Washington's Applied Physics Laboratory and the University of Colorado's National Snow and Ice Data Center. The paper comes a year after a study in the journal Science revealed that discharge from Greenland's glaciers had doubled between 2000 and 2005, leading some scientists to speculate such changes were on a steady, upward climb.
"While the rates of shrinking of these two glaciers have stabilized, we don't know whether they will remain stable, grow or continue to collapse in the near future," Howat says. That's because the glaciers' shape changed greatly, becoming stretched and thinned.
"Our main point is that the behavior of these glaciers can change a lot from year to year, so we can't assume to know the future behavior from short records of recent changes," he says. "Future warming may lead to rapid pulses of retreat and increased discharge rather than a long, steady drawdown."
The findings come on the heels of the widely publicized Intergovernmental Panel of Climate Change's report issued Feb. 2. Some scientists criticized the report for disregarding the surprisingly high discharges of ice from Greenland's glaciers since 2000 when the panel estimated the amount of future sea level rise that will be caused by melting glaciers.
In the summary for policy makers (http://www.ipcc.ch/SPM2feb07.pdf), the Intergovernmental Panel on Climate Change explained its position saying, "Dynamical processes related to ice flow and not included in current models but suggested by recent observations could increase the vulnerability of the ice sheets to warming, increasing sea level rise. Understanding of these processes is limited and there is no consensus on their magnitude."
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