COPENHAGEN - ONLY months before make-or-break UN climate talks in Copenhagen, an extraordinary conclave of climate scientists gathering here on Tuesday are expected to warn that global warming is accelerating more quickly than forecast by a key UN report for policymakers.

The UN Intergovernmental Panel on Climate Change (IPCC) concluded in early 2007 that global warming, if unchecked, would unleash a devastating amalgam of floods, drought, disease and extreme weather by century's end.

But a welter of new research suggests the impact could be even worse, and will arrive sooner rather than later.

Most worrying, they say, is the possibility that human activity - mainly the burning of oil, gas and coal - could trigger natural drivers of global warming which, once unleashed, 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.

The three-day conference is also likely to unveil a new scientific consensus that sea levels are set to rise at least a metre by 2100, more than double the IPCC estimate, which failed to take melt-off from the Greenland Ice Sheet into account.

'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.

Howard will present evidence showing for the first time that ocean acidification caused by climate change is stripping away the calcium-based shells of tiny organisms, called forams, that play a vital role in absorbing huge amounts of carbon pollution from the atmosphere.

'The policymakers that are meeting in Copenhagen in December need to consider this and other impacts in addition to what they traditionally think of as climate change,' he told AFP.

More than 2,000 scientists and 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. -- AFP