Science Magazine:glaciers not on simple upward melting trend
http://newsbusters.org/node/10804
Published Online February 8, 2007
Science DOI: 10.1126/science.1138478
Submitted on December 6, 2006
Accepted on January 24, 2007
Rapid Changes in Ice Discharge from Greenland Outlet Glaciers
Ian M. Howat 1*, Ian R. Joughin 2, Ted A. Scambos 3
1 Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Street, Seattle, WA 98105-6698, USA; National Snow and Ice Data Center, University of Colorado, 1540 30th Street, Boulder, CO, 80309-0449, USA.
2 Polar Science Center, Applied Physics Lab, University of Washington, 1013 NE 40th Street, Seattle, WA 98105-6698, USA.
3 National Snow and Ice Data Center, University of Colorado, 1540 30th Street, Boulder, CO, 80309-0449, USA.
* To whom correspondence should be addressed.
Ian M. Howat , E-mail: ihowat@apl.washington.edu
Using satellite-derived surface elevation and velocity data, we find major short-term variations in recent ice discharge and mass-loss at two of Greenland's largest outlet glaciers. Their combined rate of mass-loss doubled in less than a year in 2004 and then decreased in 2006 to near the previous rates, likely due to fast re-equilibration of calving front geometry following retreat. Total mass-loss is a fraction of concurrent gravity-derived estimates, pointing to an alternative source of loss and the need for high-resolution observations of outlet dynamics and glacier geometry for sea-level rise predictions.
http://www.sciencemag.org/cgi/content/abstract/1138478v1
By: University of Washington
Published: Feb 13, 2007 at 06:42
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."
"I think the IPCC authors made a responsible decision in producing their estimates while noting the recent discharges are a real concern that we do not yet understand well enough to make accurate predictions," says Ian Joughin, a glaciologist with the UW's Applied Physics Laboratory and co-author on the Science Express article...
http://www.yubanet.com/artman/publish/article_51099.shtml
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