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An explorer looks on in the Pastoruri glacier in Huaraz in November 2006. Ice atop the Cordillera Blanca, the largest glacier chain in the tropics, is melting quickly because of rising temperatures. ((Karel Navarro/Associated Press))

The world's largest tropical glacier is in danger of disappearing within five years, according to international researchers meeting this week in San Francisco.

Ohio State glaciologist Lonnie Thompson and a team of scientists said they have found evidence the Qori Kalis glacier of the Quelccaya ice cap in the Peruvian Andes could lose half its mass in 12 months and could be gone five years from now.

Thompson gave his presentation Thursday at the meeting of the American Association for the Advancement of Science. He told reporters afterward there was little mankind could do to stop the decline of the glacier and others like it.

"The lower elevation tropical glaciers are going right now, no matter what we do we're going to lose the glaciers on [Mount] Kilimanjaro and we're going to lose the lower elevation glaciers in the Andes," said Thompson.

The Quelccaya ice cap covers 44 square kilometres in the Cordillera Oriental region and is the world's largest tropical ice mass. Its biggest glacier, the Qori Kalis, has receded by at least 1.1 kilometres since 1963, when the first formal measurements were taken. The rate of retreat has increased from six metres per year between 1963and 1978 to 60 metres per year now, said Thompson.

The region also includes Peru's Cordillera Blanca, or White Mountain Range, one of the Andean country's most famous natural landmarks.

Climate change research has focused on melting glaciers in the north and south poles, but tropical glaciers also play a valuable role in local ecosystems as they feed rivers that supply fresh water to areas like Peru's arid coast.

Thompson worries the problem of global warming won't be addressed until things get worse.

"The question is, how far down this road do we go before there's any meaningful action to reduce emissions, what does the evidence have to be?" he said. "And unfortunately as human beings — it doesn't matter really what it is — we only deal well with crises."

The UN Intergovernmental Panel on Climate Change issued a report two weeks ago saying evidence of global warming was "unequivocal" and that man-made greenhouse gases were "very likely" behind the rising temperatures and sea levels.

The second of four reports from the panel identifying at-risk regions will be released April 6.

With files from the Associated Press