Friday, May 18, 2007

Arctic Ice Retreating 30 Years Ahead of Projections

BOULDER, Colorado, April 30, 2007 (ENS) - Arctic sea ice is melting much more quickly than projected by even the most advanced computer models, a new government funded study has found. Comparing actual ice observations with climate models, the scientists conclude that the Arctic could be seasonally free of sea ice as early as 2020.

Scientists at the National Center for Atmospheric Research and the University of Colorado's National Snow and Ice Data Center have demonstrated that the Arctic's ice cover is retreating more rapidly than estimated by any of the 18 computer models used by the Intergovernmental Panel on Climate Change in preparing its 2007 assessments.

"While the ice is disappearing faster than the computer models indicate, both observations and the models point in the same direction - the Arctic is losing ice at an increasingly rapid pace and the impact of greenhouse gases is growing," says co-author Marika Holland of the National Center for Atmospheric Research, NCAR.

Arctic Ocean sea ice breaking up in March (Photo by James Hannigan ©UCAR)
Whereas the computer models indicate that about half of the ice loss from 1979 to 2006 was due to increased greenhouse gases, and the other half due to natural variations in the climate system, the new study indicates that greenhouse gases may be playing a significantly greater role.

The study, "Arctic Sea Ice Decline: Faster Than Forecast?" will appear Tuesday in the online edition of "Geophysical Research Letters." It was led by Julienne Stroeve of the National Snow and Ice Data Center and funded by the National Science Foundation and by NASA.

The authors arrived at their conclusions by comparing model simulations of past Arctic climate and sea ice conditions with observations by satellites and other instruments.

Satellites have flown over the Arctic and looked at sea ice since 1978. Some sea ice melts in the summer every year, even in the Arctic, where temperatures are still near freezing. But in 2002, satellites showed that the springtime melting of sea ice started earlier than normal.

Satellites helped scientists learn that there was about 502,000 square miles less sea ice each September since 2001 than there typically was in previous Septembers. September marks the yearly minimum of sea ice in the Arctic.

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