Polar bears’ ice not so thin after all

U. WASHINGTON (US) — The fate of polar bear may not be as grim as previously thought.

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.

Now scientists believe 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,” says 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.”

The earlier study projected 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—leading to the 2008 listing of polar bears as a threatened species.

The new research, published in the Dec. 16 issue of Nature, indicates there is no “tipping point” that would result in unstoppable loss of summer sea ice when greenhouse gas-driven warming rises above a certain threshold.

“Our research offers a very promising, hopeful message, but it’s also an incentive for mitigating greenhouse emissions,” says Cecilia Bitz, associate professor of atmospheric sciences at the University of Washington.

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 largely disappeared altogether in following decades.

However, the new study indicates that if greenhouse gas emissions are reduced substantially in the near future, rapid ice losses will be followed by substantial retention of the remaining ice through this century, as well as partial recovery of the ice that disappeared during the rapid ice loss.

Polar bears depend on sea ice for access to ringed and bearded seals, their primary food source. During seasons when they can’t reach sea ice, the bears mostly go without food and can lose about 2 pounds a day.

The periods when they don’t have ice access have increased and are expected to continue increasing with the current level of greenhouse gas emissions.

For the study, Amstrup divided the Arctic into four separate ecoregions according to the nature of ice typically found there. The 2007 study showed a very high likelihood that polar bears would become extinct in two of those regions given current trends in greenhouse gas emissions.

“There’s still a fairly high probability in both of those regions that polar bears could disappear,”Amstrup says.

“But with mitigation and aggressive management of hunting and other direct bear-human interactions, the probability of extinction would now be lower than the probability that polar bear numbers will simply be reduced.

“With mitigation, conditions for polar bears might even improve in the other two ecoregions. The benefit of mitigation to polar bears is substantial.”

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