The finding is part of a year-long review of the effects of climate and ice changes on polar bears, to help determine whe-

ther they should be protected under the Endangered Species Act. Scientists estimate the current polar bear population at 22,000.

The report, which the US Geological Survey released on Friday, offered stark prospects for polar bears.

Biologists and climate scientists concluded that under moderate projections for global warming, by mid-century, the bears will be largely relegated to the Arctic archipelago of Canada and spots off the northern Greenland coast, where sea ice persists even in warm summers.

This shrinking of their habitat could reduce the polar 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,' said Mr Steven Amstrup, lead biologist for the survey team.

In the report, the team said: '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 population.

A separate new analysis by scientists from the National Oceanic and Atmospheric Administration, published on Saturday in the journal Geophysical Research Letters, says sea ice coverage of the Arctic Ocean will decline by more than 40 per cent before the summer of 2050.

In a conference call with reporters on Friday, the Survey scientists 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 happens with emissions.

In other words, even in the unlikely event that all the major economies agree to rapid and drastic reductions in emissions of greenhouse gases, the floating Arctic ice cap will continue to shrink at a rapid pace for the next 50 years, wiping out much of the polar bears' habitat.

A decision on listing the bears as a threatened species will be made by another agency of the Interior Department, the Fish and Wildlife Service, in January, officials have said.

NEW YORK TIMES