The Jakobshavn Glacier, on Greenland's west coast, is melting twice as fast as 10 years ago and advancing toward the sea at 12 kilometres (seven miles) per year, compared with six kilometres (three and a half miles) before.

In its 4th Assessment report issued earlier this year, the UN's Intergovernmental Panel on Climate Change (IPCC) said the world's oceans could rise by 50 centimeters (20 inches), putting tens of millions, perhaps hundreds of millions of people at risk by century's end.

But that estimate does not factor in the latest findings about the melting of glaciers in Greenland and loss of ice in Antarctica, which many experts say could eventually increase sea levels, and the rate at which they rise, by several fold.

Jakobshavn, moving toward the ocean at a clip of 30 to 40 metres a day, is but a single icy tongue reaching out from the Greenland icesheet, a massive block of ice and snow up to three kilometres (1.9 miles) thick covering 80 percent of the island, which is four times the size of France.

If the sheet's entire 2.85 million cubic kilometres (685,000 cubic miles) of ice were to melt, it would lift sea levels by seven metres (23 feet), swamping every major coastal city in the world.

Even in worst-case scenarios, such a meltdown would happen over centuries, not decades. But what scientists fear most is the "tipping point" beyond which the loss of ice becomes a self-reinforcing, positive feedback loop.

As sea ice -- the focus of the International Polar Day -- continues to recede, it gives rise to a phenomenon called albedo.

Albedo is the reflectivity of light. Because sea ice has a bright surface, most of the solar energy that strikes it is reflected back into space.

When that ice covering is replaced by dark-blue sea, however, the heat is absorbed, thus accelerating the melt.

"Over the last 30 years, temperatures have been rising twice as fast at the poles as the rest of the planet, which means that if we are looking at a global rise of 2 degrees C (3.6 F) by century's end, we will probably have an increase of 4 degrees C (7.2 F) here," said French scientist Jean Jouzel, accompanying French environment minister Jean-Louis Borloo to Greenland on a fact-finding mission.

These rising temperatures have resulted in a dramatic shrinkage of the ice covering the Arctic, with the total surface area dropping from four to three million square kilometres (1.15 million square miles) in just one year, the European Space Agency (ESA) said last week.

That has created a lot of newly-exposed blue water, and is tenfold the yearly average of ice cover lost over the previous decade.

Jakobshavn, meanwhile, continues to melt as it races -- by glacial standards -- toward the sea.

"In 1996, the glacier shed 27 cubic kilometers (6.5 cubic miles) of water per year, and today it is 50 km3 (12 cu. miles) per year. It is already too late to stop this movement, but we have compelling reasons to try to keep the temperature of the planet close to its current level," said Jouzel.

For now, Greenland accounts for about 15 percent of the world's rise in sea levels. No one can say what that figure will be in a decade or a century, but the trend is clear, said another French climatologist, Herve Le Treut.

"What is sure is that there is no way to reverse the mechanism, and we are almost sure that it will continue to rise," he said.

The International Polar Year 2007-2008 is a multi-national research effort involving 50,000 scientists from over 60 countries. Their aim is to better understand the polar regions -- their ecology and biodiversity, geological history, relation to climate change -- and raise public awareness.

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