Two-thirds of the world’s polar bears will disappear by 2050, even under moderate projections for shrinking summer sea ice caused by greenhouse gases in the atmosphere.The finding is part of a yearlong review of the effects of climate and ice changes on polar bears to help determine whether they should be protected under the Endangered Species Act. Scientists estimate the current polar bear population at 22,000.

The scientists concluded that, while the bears were not likely to be driven to extinction, they would be largely relegated to the Arctic archipelago of Canada and spots off the northern Greenland coast, where summer sea ice tends to persist even in warm summers like this one, a shrinking that could be enough to reduce the bear population by two-thirds. The bears would disappear entirely from Alaska, the study said. “As the sea ice goes, so goes the polar bear”.

Sea ice conditions would have to be substantially better than even the most conservative computer simulations of warming and sea ice to avoid the anticipated drop in bear population.The scientists also said the momentum to a warmer world with less Arctic sea ice — and fewer bears — would be largely unavoidable at least for decades, no matter what happened with emissions of heat-trapping gases like carbon dioxide. Even in the unlikely event that all the major economies were to agree to rapid and drastic reductions in emissions of carbon dioxide and other heat-trapping gases, the floating Arctic ice cap will continue to shrink at a rapid pace for the next 50 years, wiping out much of the bears’ habitat.

In some places, the bears have adapted to eating a wide range of food like snow geese and garbage. But the survey team said their fate was 84 percent linked to the extent of sea ice.Sea-ice coverage of the Arctic Ocean will decline by more than 40 percent before the summer of 2050, compared with the average ice extent from 1979 to 1999. This summer the ice retreated much farther and faster than in any year since satellite tracking began in 1979.