Sea levels this century may rise several times higher than predictions made in 2007 that form the scientific foundation for policymakers today, the meeting heard.

In March 2007, the UN's Intergovernmental Panel on Climate Change (IPCC) concluded that global warming, if unchecked, would lead to a devastating amalgam of floods, drought, disease and extreme weather by the century end.

The world's oceans would creep up 18 to 59 centimetres (7 to 23 inches), enough to wipe out several small island nations, and wreak havoc for tens of millions living in low-lying deltas in east Asia, the Indian subcontinent and Africa.

But a new study, presented at the Copenhagen meeting on Tuesday, factored in likely water runoff from disintegrating glaciers in Greenland and Antarctica, and found the rise could be much higher.

The IPCC estimate had been based largely on the expansion of oceans from higher temperatures, rather than meltwater and the impact of glaciers tumbling into the sea.

Using the new model, "we get a range of sea level rise by 2100 between 75 and 190 centimetres when we apply the IPCC's temperature scenarios for the future," said climate expert Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research.

Even if the world manages to dramatically cut the emission of greenhouse gases driving global warming, the "best estimate" is about one metre (3.25 feet), he said.

"A few years ago, those of us who talked about the impact of the ice sheets were seen as extremists. Today it is recognized as the central issue," said glaciologist Eric Rignot of the University of California at Irvine.

"The world has very little time," IPCC chief Rajendra Pachauri told the meeting after the new findings were presented.

Participants also spoke out about fears that greenhouse gases -- mainly emissions from oil, gas and coal -- could trigger tipping points that would be nearly impossible to reverse.

The shrinking of the Arctic ice cap, and the release of billions of tonnes of greenhouse gases trapped in melting permafrost are two such "positive feedbacks" that could become both cause and consequence of global warming.

"We need to look at what is a 'reasonable worst case' in the lifetime of people alive today," said John Ashton, Britain's top climate negotiator, noting even rich nations had yet to take such scenarios seriously.

"A sea level rise of one or two meters would not just be damaging for China, it would be an absolute catastrophe. And what is catastrophic for China is catastrophic for the world," he said.

Up to 600 million people living close to coast lines in poor and rich countries alike could be affected, said Konrad Steffen, head of the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorodo.

"They will have to move -- it would change the whole structure of populations, and we know had badly we deal with migration," he told AFP.

Among the worst hit countries will be Bangladesh, which would lose some 17 percent of its landmass, displacing nearly 15 million people.

"These startling new predictions on sea levels rise spell disaster for millions of the world's poorest people," said Rob Bailey of Oxfam. "This must be a wakeup call for rich countries are not doing anywhere near enough to prevent these cataclysmic predictions becoming a reality."

More than 2,000 researchers from 80 countries responded to the open invitation to present their findings, which were then vetted by a panel of climate experts, many of them top figures in the IPCC.

"I and a lot of scientists see this meeting as an opportunity to update the science that has come out since the last IPCC report," said William Howard, a researcher from the University of Tasmania in Hobart, Australia.

"The huge response from scientists comes from a sense of urgency, but also a sense of frustration," said Katherine Richardson, head of the Danish government's Commission on Climate Change Policy.

Richardson said the 2007 IPCC report, called the Fourth Assessment Report, was an invaluable document but it would be years out of date when negotiators convene in Copenhagen in December to hammer out a global climate treaty.

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