October 3, 2011
Climate activists Lesley Butler and Rob Bell (R) "sunbathe" on the edge of a frozen fjord in the Norwegian Arctic town of Longyearbyen April 25, 2007. REUTERS/Francois Lenoir
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SINGAPORE (Reuters) - A huge hole that appeared in the Earth's protective ozone layer above the Arctic in 2011 was the largest recorded in the Northern Hemisphere, triggering worries the event could occur again and be even worse, scientists said in a report on Monday.