Extinction could be approaching.

Bears are dependent on sea ice because they use it to hunt for seals, which periodically pop up through breathing holes in the ice. Be said the Arctic Climate Impact Assessment, the product of four years of work by more than 300 scientistscause the ice has broken up earlier and earlier in the year over the past few decades, polar bears are deprived of crucial hunting opportunities.

The thinning of sea ice -- which is projected to shrink by at least half by the end of the century and could disappear altogether, according to some computer models -- could determine the fate of many other key Arctic species,.