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The steady disappearance of Arctic sea ice, which is causing the exposed and darker surface of the Arctic Ocean to absorb more sunlight, is having a more profound impact on global warming than previouslyestimated, according to a new study. The decline of albedo, or reflectivity, from the Arctic Ocean equals roughly 25 percent of the warming caused by rising carbon dioxide levels, according to scientists at the University of California, San Diego. The impact of this “albedo feedback,” in which the highly reflective white surface of sea ice is replaced by heat-absorbing open ocean, is considerably stronger than climate models had predicted, according to the UCSD research , published in the Proceedings of the National Academy of Sciences. Researchers had thought increasing Arctic cloud cover might slow the albedo feedback, but this study indicates that is not happening.