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美国：北极熊命运堪忧 Most polar bears could be lost by 2050 "There is a definite link between changes in the sea ice and the welfare of polar bears," said Steve Amstrup, who led the research team. Arctic sea ice is already at an all-time low this year and is expected to retreat farther this month, according to the US National Snow and Ice Data Center. That means that polar bears -- some 16,000 of them -- will disappear by 2050 from parts of the Arctic where sea ice is melting most rapidly, along the north coasts of Alaska and Russia, researchers said. Other polar bear populations could survive beyond that date but many of those could be gone by 2100, Amstrup said. By century's end, the only polar bears left might live in the Canadian Arctic islands and along the west coast of Greenland. "Projected changes in future sea ice conditions, if realized, will result in loss of approximately two-thirds of the world's current polar bear population by the mid 21st century," the report's executive summary said. "Because the observed trajectory of Arctic sea ice decline appears to be underestimated by currently available models, this assessment of future polar bear status may be conservative." In January, the US Fish and Wildlife Service proposed listing the polar bear as a threatened species under the Endangered Species Act, noting polar bears depended on sea ice as a platform to hunt seals, their main prey. | 
