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. Last Updated: 07/27/2016

Polar Bears May Be on Thin Ice

WASHINGTON -- Two-thirds of the world's polar bears will be killed off by 2050 -- and the entire population gone from Alaska -- because of thinning sea ice from global warming in the Arctic, U.S. government scientists forecast.

Only on the northern Canadian Arctic islands and the west coast of Greenland are any of the world's 16,000 polar bears expected to survive through the end of the century, said the U.S. Geological Survey, which is the scientific arm of the Interior Department.

USGS projects that during the next half-century, polar bears will disappear along the north coasts of Alaska and Russia and lose 42 percent of the Arctic range that they need to live in during the summer, when they hunt and breed. A polar bear usually lives about 30 years.

"Projected changes in future sea ice conditions, if realized, will result in the loss of approximately two-thirds of the world's current polar bear population by the mid-21st century," said the report, which was released Friday.

Polar bears depend on sea ice as a platform for hunting seals, which are their primary food. They rarely catch seals on land or in open water. Because the general decline of Arctic sea ice appears to be underestimated, scientists said their forecast of how much polar bear populations will shrink also might be on the low side.

"There is a definite link between changes in the sea ice and the welfare of polar bears," said USGS scientist Steven Amstrup, the lead author of the new studies. "As the sea ice goes, so goes the polar bear."

Amstrup said 84 percent of the scientific variables affecting the polar bear's fate was tied to changes in sea ice.

As of this week, the extent of Arctic sea ice had fallen to 12.3 million square kilometers -- 647,500 square kilometers below the previous record low, in September 2005, according to the National Snow and Ice Data Center.

Scientists do not hold out much hope that the buildup of carbon dioxide and other industrial gases blamed for heating the atmosphere can be turned around in time to help the polar bears.

Polar bears have walked the planet for at least 40,000 years.

"In spite of any mitigation of greenhouse gases, we are going to see the same amount of energy in the system for at least 20, 30, 40 years," USGS director Mark Myers said.

Greenland and Norway have the most polar bears, while one-quarter of them live mainly in Alaska and travel to Canada and Russia. The agency said their range would no longer include Alaska and other southern regions.

The findings of U.S. and Canadian scientists are based on six months of new studies, during which the health of three polar bear groups and their dependency on Arctic sea ice were examined using new and traditional models, Myers said.

USGS issued nine separate reports on polar bears Friday. They were made public to help guide Interior Secretary Dirk Kempthorne's decision, expected in January, on his agency's proposal to add the polar bear to the government's endangered species list.

In December, Kempthorne proposed designating polar bears a "threatened" species deserving federal protection under the Endangered Species Act because of melting Arctic sea ice from global warming. That category is second to "endangered" on the government's list of species believed most likely to become extinct.

That action is in response to a lawsuit in 2005 by three environmental groups -- the Center for Biological Diversity, Natural Resources Defense Council and Greenpeace -- to force such a proposal from Interior's Fish and Wildlife Service, which oversees endangered species.

USGS declined to provide precise estimates of polar bear populations 50 years from now.