It is reported that sea level is rising at a rapid speed and may lead flooding several cities until some major preventive steps are taken to check the carbon dioxide emissions.

The scientists feel that the earth will soon see a huge retreat of ice sheets once a threshold of warming crosses the danger point.

According to Roger Highfield, Science Editor of News.telegraph, "that the rise would produce a catastrophic sea level rise of at least 20ft, drowning the centre of London and displacing millions in Britain alone".

Temperatures are rising on track to melt the Greenland and Antarctic ice sheets sooner than thought, triggering the 20ft sea rise by 2600 and inundating heavily-populated coastal areas, including much of the Netherlands.

Two international teams report today in the journal Science that Arctic summers by 2100 may be as warm or warmer than they were nearly 130,000 years ago, when sea levels eventually rose up to 20ft higher than today. Such a rise had been thought to be at least 1,000 years away.

The work is "fascinating and scary at the same time", said Prof Michael Oppenheimer of Princeton University. "We should take this as a serious warning sign."

Profs Bette Otto-Bliesner and Jonathan Overpeck report the findings with colleagues from the National Centre for Atmospheric Research in Boulder, Colorado, US Geological Survey and universities and organizations worldwide.

"This is a real eye-opener," said Prof Overpeck. "We could have a six metre sea level rise as early as 2600 - 500 years from now. If we warm the Arctic (and Antarctic) more than it warmed 129,000 years ago, then the rate of ice sheet retreat and sea level rise could be even greater."

Prof Bill McGuire, of the Benfield Hazard Research Centre, University College London, said: "Last year a six metre [20ft] rise was thought to be at least 1,000 years away. This year it is 500 as the Greenland ice sheet continues to fall apart at an accelerating rate."

The Benfield team has predicted that a 20ft rise would leave many towns and cities, including Edinburgh, Newcastle, Bristol, Plymouth, Norwich, Peterborough and Bournemouth, waterlogged, with well over two million people displaced.

In the London area, much of Southwark, Lewisham, Greenwich, Tower Hamlets, Bexley and Barking and Dagenham would be under water, along with large areas of south Essex and north Kent earmarked for the Thames Gateway Development.

Prof McGuire said a "doomsday" scenario would see a 275ft rise but this was extremely unlikely and would only happen if we do nothing about carbon emissions, leading to a runaway greenhouse effect.