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FILE - This undated file photo released by the U.S. Fish and Wildlife Service shows a sow polar bear resting with her cubs on the pack ice in the Beaufort Sea in northern Alaska. A federal judge on Monday, Oct. 17, 2011, threw out a key section of an Interior Department rule that declared global warming is threatening the survival of the polar bear. (AP Photo/U.S. Fish and Wild Life Service, Steve Amstrup, FILE)

FILE - This undated file photo released by the U.S. Fish and Wildlife Service shows a sow polar bear resting with her cubs on the pack ice in the Beaufort Sea in northern Alaska. A federal judge on Monday, Oct. 17, 2011, threw out a key section of an Interior Department rule that declared global warming is threatening the survival of the polar bear. (AP Photo/U.S. Fish and Wild Life Service, Steve Amstrup, FILE)

Huge crack discovered in Antarctic glacier

A major glacier in Antarctica is melting unusually quickly because ocean currents are undermining it from below, researchers find. Scientists are gathering meaningful and accurate data of how ice sheets and glaciers are changing over time, and what this means for our planet.