From Scientific American:
Two-thirds of the world’s current polar bear population could be gone by midcentury if predictions of melting sea ice hold true, the U.S. Geological Survey reported on Friday. The fate of polar bears might be even more imperiled than that estimate, because sea ice in the Arctic might be vanishing faster than the available computer models predict, the geological survey said in a report aimed at determining whether the arctic bear should be classified as a threatened species.
More here.