FILE - In this Sept. 13, 2006 file photo, ice chunks float in the Arctic Ocean as the sun sets near Barrow, Alaska. The Arctic is a thermostat against overheating and a barometer of change, but now its own protective ozone layer that keeps out damaging ultraviolet radiation has thinned to record levels, the U.N. weather agency said Tuesday April 5, 2011. (AP Photo/Arctic Sounder, Beth Ipsen)
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