TWO major glaciers in Greenland have recently begun to flow and break up more quickly under the onslaught of global warming, according to a new study which has raised the spectre of millions drowning from rising sea levels.The report by the University of Swansea's School of the Environment and Society said the Kangerdlugssuaq and Helheim glaciers had doubled their rate of flow to the ocean over the past two years after steady movement during the 1990s.

This spurt meant that current environmental models of the rate of retreat of Greenland's giant ice sheet – which could add seven metres to the height of the world's oceans if it disappears – had underestimated the problem.

"It seems likely that other Greenland outlets will undergo similar changes, which would impact the mass balance of the ice sheet more rapidly than predicted," the study said.

It said the fact that the two major outflow glaciers had shown the same sudden acceleration despite being more than 300km apart suggested the cause was not local but more likely climatic or oceanic in origin.

"In both of these glaciers the acceleration and retreat has been sudden, despite the progressive nature of warming and thinning over some years," the report said.

Advertisement:"The longevity of this flux increase is unknown but could be substantial," it added.

The report followed a warning earlier this week from Britain's Hadley Centre for Climate Prediction and Research – a branch of the Meteorological Office – that the Greenland ice sheet could be disappearing faster than previously thought.

The ice sheet contains one-tenth of the world's freshwater reserves.

Scientists predict that global average temperatures will rise by between one and six degrees Celsius this century unless urgent action is taken now to cap and reduce carbon emissions.

Even a rise of three degrees could result in cataclysmic species loss, melting polar icecaps raising sea levels by many metres and wholesale famine and disease.

Greenland is only part of the picture, and there is also evidence of local warming and melting on the giant Western Antarctic ice sheet.

Scientists said on Monday the world had to halt greenhouse gas emissions and reverse them within two decades or watch the planet spiralling towards destruction.

The first phase of the global Kyoto protocol on cutting greenhouse gas emissions runs until 2012, and negotiations have only just started on finding a way of taking it beyond that.

The United States, the world's biggest polluter, has rejected both the protocol in its current form and any suggestion of expanding or extending it.