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Polar bear 'doomed'? Only if greenhouse-gas emissions aren't cut.

Greenhouse-gas emissions worldwide must be cut to avoid a disappearance of summer sea ice in the Arctic, which is crucial to the polar bear.

By Staff writer / December 15, 2010

In this undated file photo, a polar bear is shown in the Arctic National Wildlife Refuge in Alaska.

Subhankar Banerjee/AP/File

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Polar bears – the white-furred poster children for global warming's impact on the Arctic – could step back from the brink of extinction over the course of this century if concerted efforts are made to reduce greenhouse-gas emissions and if rigorous wildlife management efforts are undertaken to keep bears and people safely apart.

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That's the simple message behind a modeling study unveiled Wednesday by a team of federal and university scientists specializing in Arctic climate and polar-bear ecology.

In some respects, the conclusion isn't surprising, say some researchers who were not involved in the study. But, they add, buried in the study's details is a change in expectations for how the Arctic Ocean's sea ice is likely to behave as the climate warms. This change, if born out in the real world, could give Ursus maritimus more ice rafts to clamber over than might otherwise be the case.

"This is hopeful news for polar bears," says Walt Meier, a researcher with the National Snow and Ice Data Center at the University of Colorado at Boulder.

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The study is being released even as environmentalists and scientists are pressing the federal government to list the bears as "endangered." In November, a US district court ruled that the Interior Department had to take a second look at its 2008 decision to list the bears as "threatened," rather than the more-dire "endangered." The department must turn its latest evaluation over to the court by Dec. 23.

Perched at the top of the Arctic food chain, polar bears are seen as key indicators of the overall health of the marine environment above the Arctic Circle.

Three years ago, summer sea ice that the bears rely on as platforms for hunting seals, as well as for breeding, receded the furthest since satellites first began monitoring sea-ice coverage in the Arctic Ocean in 1979.

Many specialists attributed the decline to the effects of global warming, as well as to changes in seasonal wind patters that drove broken sea ice out of the Arctic basin and into the North Atlantic, researchers noted.

The dramatic retreat of Arctic sea ice in the summer of 2007 prompted some researchers to warn that the system may have reached a tipping point that would lead to the disappearance of summer sea ice within the next several decades, regardless of actions humans took to reduce greenhouse-gas emissions.

That concern, in turn, helped elevate the polar bear to climate-icon status and reportedly fed into then-President George W. Bush's decision in 2008 to list the bear as "threatened" under the Endangered Species Act.

No 'tipping point'

The new study, however, finds no "tipping point" now or in this century in Arctic sea-ice decline, but rather a relatively steady fall-off in ice extent as average temperatures increase.

The study's authors say that this gives cause for hope that once greenhouse-gas concentrations stabilize, the average temperatures in the Arctic would respond in ways that would keep the sea ice from declining further, although natural shifts in seasonal weather patterns would continue to play its role in varying sea-ice extent from one year to the next.

"Polar bears do not appear to be doomed by what we have contributed already" to atmospheric concentrations of greenhouse gases, says Cecilia Bitz, an atmospheric scientist at the University of Washington in Seattle and a member of the team reporting its results in Thursday's issue of the journal Nature.

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