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This would give a total potential temperature rise of 2.5C – 4.7C. There was even an outside chance of much greater warming, of around 7C, he said.

He said: “There is no room now to argue that the earth is warming. Sadly policy makers have shied away from such findings and that is why there is no concensus on where to stabilise global temperatures or how,” he said. Even a minimal temperature change of 1C would put food security and water availability at risk.”

Other scientists were equally gloomy on the impacts of rising sea level, warning that rising oceans would have major impacts around the world and were likely to hit low-lying countries, particularly hard. Countries like Bangladesh, China, the Mumbai region of India were especially at risk but even developed ones like Britain would be affected badly.

Dr John Church of the Centre for Australian Weather and Climate Research, Hobart, Tasmania, Australia, told the conference, sea level rise by 2100 could be in the range of about one meter, or possibly more.

The warning comes from new research into the behaviour of glaciers and ice sheets, especially in Greenland. It had been thought the main effect of global warming was simply to melt them.

However, the new research shows that as water melts it sinks down to the bedrock under the glaciers and lubricates them, so that their movement to the sea accelerates sharply.

This has turned out to be a much more powerful effect than simple melting and means the IPCC, whose 2007 report projected a sea level rise of 18 - 59 cm by 2100, must once again revise its earlier findings.

Eric Rignot, Professor of Earth System Science at the University of California Irvine and Senior Research Scientist at NASA's Jet Propulsion Laboratory said the finding had emerged from research conducted after the IPCC report was written.

He said: “As a result of the acceleration of outlet glaciers over large regions, the ice sheets in Greenland and Antarctica are already contributing more and faster to sea level rise than anticipated. If this trend continues, we are likely to witness sea level rise one meter or more by year 2100.”

The point of the Copenhagen meeting is to draw together all the latest science on climate change in preparation for the UN negotiations planned for this December at which politicians will try to draw up a replacement for the Kyoto treaty on reducing greenhouse gases, which expires in 2012.

However, John Ashton, a senior civil servant at the British Foreign Office, launched a startling attack – for a government official – on the ability of politicians to deal with climate change, or even understand it.

He said he believed politicians had still failed to grasp the seriousness of climate change – or were even prepared to bend scientific findings to purely political ends.

"Policymaking is not adapted to deal with the problem of climate change, " said Ashton. “Politiicans often see science as just another group and that opinions based on science are just another lobby. There are also plenty of people who due to ignorance or mischief are willing to confuse the issue.”

Ashton did not name any particular politicians or issues but his comments come just weeks after the government gave its approval to the building of a third runway at Heathrow airport, an issue which is said to have left many of Britain’s climate policy-makers seething.

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