Reuters: A deep freeze holding 90 percent of the world’s ice, Antarctica is one of the biggest puzzles in debate on global warming with risks that any thaw could raise sea levels faster than U.N. projections. Even if a fraction melted, Antarctica could damage nations from Bangladesh to Tuvalu in the Pacific and cities from Shanghai to New York. It has enough ice to raise sea levels by 57 metres if it melted, over thousands of years. A year after the U.N.’s Intergovernmental Panel on …