for National Geographic News
Two-thirds of the world's polar bears could disappear by 2050 as global warming continues to melt the Arctic's sea ice, according to a series of U.S. government studies released last Friday.
The new findings paint a sobering picture for polar bears, whose dependence on sea ice makes them particularly vulnerable to warming temperatures.
"Our results have demonstrated that as the sea ice goes, so goes the polar bear," said Steven Amstrup, a U.S. Geological Survey (USGS) wildlife research biologist in Anchorage, Alaska, and leader of the polar bear studies.
USGS conducted the studies to help the U.S. Fish and Wildlife Service determine whether polar bears warrant protection under the U.S. Endangered Species Act. That decision is due in January 2008.
(Read: "Polar Bears Proposed for U.S. Endangered Species List" [December 27, 2006].)
Kassie Siegel is a climate change activist with the Center for Biological Diversity in Joshua Tree, California. The new studies, she said, represent a watershed moment in the climate crisis.
"If we don't change the path that we're on now, then it will be too late," she said. "Polar bears will become extinct."
Polar Bears and Sea Ice
Scientists estimate that 20,000 to 25,000 polar bears live throughout the Northern Hemisphere in areas that are covered by sea ice for extensive periods.
Polar bears eat mostly seals and other fatty marine mammals that they hunt from the ice.
In some places—like the southern end of polar bear range in Canada's Hudson Bay—the sea ice melts in the summer. The bears then come onto land, where they have insufficient food until the sea ice refreezes in the fall.
Those bears, USGS's Amstrup said, may be the first to die off. As the sea ice melts sooner each summer, the bears will be forced to come ashore earlier and face food shortages before they have stored enough fat to last through the season.
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