Posts Tagged ‘ Climate ’

Polar Bears Still on Thin Ice, but Cutting Greenhouse Gases Now Can Avert Extinction, Experts Say

Polar Bears Still on Thin IceScienceDaily (Dec. 15, 2010) โ€” Polar bears were added to the threatened species list nearly three years ago as their icy habitat showed steady, precipitous decline because of a warming climate. But it appears the Arctic icons aren’t necessarily doomed after all.

Scientists from several institutions, including the U.S. Geological Survey and the University of Washington, have found that if humans reduce greenhouse gas emissions significantly in the next decade or two, enough Arctic ice is likely to remain intact during late summer and early autumn for polar bears to survive.

“What we projected in 2007 was based solely on the business-as-usual greenhouse gas scenario,” said Steven Amstrup, an emeritus researcher with the U.S. Geological Survey and the senior scientist with the Montana-based conservation organization Polar Bears International. “That was a pretty dire outlook, but it didn’t consider the possibility of greenhouse gas mitigation.”

That study projected that only about one-third of the world’s 22,000 polar bears might be left by mid-century if the dramatic Arctic ice decline continued, and that eventually they could disappear completely. The work led to the 2008 listing of polar bears as a threatened species.

The new research, published in the Dec. 16 issue of Nature, is based in part on modeling proposed by Cecilia Bitz, a UW associate professor of atmospheric sciences. It indicates there is no “tipping point” that would result in unstoppable loss of summer sea ice when greenhouse gas-driven warming rose above a certain threshold.

“Our research offers a very promising, hopeful message, but it’s also an incentive for mitigating greenhouse emissions,” Bitz said.

Amstrup is the lead author of the Nature paper. Besides Bitz, co-authors are Eric DeWeaver of the National Science Foundation, David Douglas and George Durner of the USGS Alaska Science Center, Bruce Marcot of the U.S. Forest Service in Oregon and David Bailey of the National Center for Atmospheric Research in Colorado.

Because the scientists were looking specifically to see if there is a tipping point beyond which seasonal Arctic ice could not recover, they used a general circulation model with a sea-ice component particularly sensitive to rising temperatures, with major parts of it designed by Bitz.

“We didn’t necessarily need to compare with other models since we were using one that is extremely sensitive in the Arctic, which allowed us to make a more conservative statement about the potential to slow the loss of sea ice,” she said.

Previous work by Bitz and others showed that unchecked temperature increases, along with natural environmental volatility, could result in the loss of vast areas of Arctic ice in less than a decade. It also showed that with continued business-as-usual greenhouse gas emissions the ice did not recover after such rapid ice losses, and it largely disappeared altogether in following decades.

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