Polar Bears' Habitat Threatened By Thinning Of Arctic Sea Ice

The thinness of the ice covering the Arctic Ocean, approximately three metres deep, makes it far more vulnerable to longer summers than the glaciers of the Antarctic. A 40% thinning of the ice has occurred since the 1960s. Polar bears rely on the ice to hunt for seals, and its earlier break-up is giving them less time to hunt. Continued decrease in the Arctic's ice cover would also act to increase the effects of global warming in the northern hemisphere by decreasing the amount of sunlight reflected by the ice. It is also believed that the Arctic ice plays a role in the operation of the Gulf Stream, and that this could be disrupted by continued thinning.

Previous studies suggesting that the decrease in ice cover was caused by changing wind patterns relied on computer models to arrive at their conclusions. The new results are based upon observation and measurements made possible by the use, for the first time, of radar data from a European Space Agency satellite and microwave images obtained from an American satellite, to determine changes in the length of the Arctic summer.

Dr Seymour Laxon, from the Centre for Polar Observation and Modelling at UCL, said: "Results from the American satellite have shown that the length of summers has increased over the last 25 years. When we compared the data from the two satellites we were astonished by the similarity between changes in the ice thickness and the length of the summer melt season. This result suggests that if this continues, further melting will occur, leading to the eventual disappearance of the ice during summer."