Agencies' report warns of faster climate change

Konrad Steffen, who directs the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder and was lead author on the report's chapter on ice sheets, said the models the intergovernment panel used did not factor in some of the dynamics that scientists now understand about ice sheet melting. Steffen and his collaborators have identified, among other things, a process of "lubrication," in which warmer ocean water gets underneath coastal ice sheets and accelerates melting.

"This has to be put into models," said Steffen, who organized a conference during the summer in St. Petersburg, Russia, as part of an effort to develop more sophisticated ice sheet models. "What we predicted is sea level rise will be higher, but I have to be honest, we cannot model it for 2100 yet."

Still, Armstrong said, the report "does take a step forward from where the [intergovernment panel] was," especially in terms of ice sheet melting.

Scientists also looked at the prospect of prolonged drought over the next 100 years. They said it was impossible to determine yet whether human activity is responsible for the drought the Southwestern United States has experienced over the last decade, but every indication suggests the region will become consistently drier in the next several decades. Richard Seager, a senior research scientist at Columbia University's Lamont-Doherty Earth Observatory, said that nearly all of the 24 computer models the group surveyed projected the same climatic conditions for the North American Southwest, which includes Mexico.

"If the models are correct, it will transition in the coming years and decades to a more arid climate, and that transition is already underway," Seager said, adding that such conditions would probably include prolonged droughts lasting more than a decade.

The current models cover broad swaths of landscape, and Seager said scientists needed to work on developing versions that can make projections on a much smaller scale.

Armstrong said the need for "downscaled models" was one of the challenges facing the federal government. When it comes to abrupt climate shifts, he said, "we need to be prepared to deal with it in terms of policymaking. . . . There are really no policies in place to deal with abrupt climate change."

Richard Moss, who worked for the Climate Change Science Program from 2000 to 2006 and now serves as vice president and managing director for climate change at the World Wildlife Fund-U.S., welcomed the report but called it "way overdue."