As a result of speedy melting of the Greenland ice sheet, the sea levels might rise three times faster than at present, by the end of the century.

Scientists warned yesterday that as a result of the global warming the quick melting of the Greenland ice sheet would increase speed of the rise in sea levels.

The researchers have also found that due to the water running off the ice sheet, the sea level would rise by 9 mm per year and the global rise would be 1 metre every century.

As a result of the increasing temperatures, already the oceans are increasing on warming and causing the sea levels to rise. Until now the scientists had less information regarding how fast the ice sheets of Greenland and Antarctica would begin to disappear.

Greenland ice sheet, covering 1.7 million square kilometers of land, has begun to melt faster and the reasons are thought to be water on the ice sheet dripping down through cracks, to the underlying bedrock and loss of buttressing ice shelves along the coastline. This all is making the ice sheet more unstable.

Researchers led by Anders Carlson at the University of Wisconsin-Madison have decided to look back to the end of last ice age for clues as the climate scientist are not certain as to how susceptible ice sheets are to global warming because they have not witnessed the disappearance of any of these.

Around 20,000 years ago, North America was covered with a giant mass of frozen water called the Laurentide, when the last ice age was at its peak. 6500 years ago this ice sheet, which was three miles thick in some places, had more or less completely melted as the world warmed as a part of its natural cycle. At that time the surface air temperatures were similar to those that are being predicted in the year 2100.

To reconstruct the demise of the Laurentide ice sheet, the researchers used the geological record and computer simulations.

By dating the boulders and fossilized organisms left on the fresh ground, after the ice sheet melted, it was found that the ice sheet saw two periods of rapid melting. Computer simulations revealed that around 9,000 years ago melting of the ice sheet caused sea levels to rise by about 7 metres at a rate of around 1.3cm a year and in the second stage of rapid melting, which began 7,500 years ago, sea levels rose by 5 metres at a rate of around 0.7cm a year.

"We have never seen an ice sheet retreat significantly or even disappear before, yet this may happen for the Greenland ice sheet in the coming centuries to millenia," said Carlson, whose study appears in the journal Nature Geoscience.

Carlson further added, "We're not talking about something catastrophic, but we could see a much bigger response in terms of sea level from the Greenland ice sheet over the next 100 years than what is currently predicted,"

Recent report of UN's Intergovernmental Panel on Climate Change predicts the sea levels to rise by about 10 cms by 2100 but Carlson's analysis suggests that the rapid melting of Greenland ice sheet would cause the sea levels to rise much greater.

Carlson further said, "For planning purposes, we should see the IPCC projections as conservative.”We think this is a very low estimate of what the Greenland ice sheet will contribute to sea level."

Mark Sidall, at Bristol University, in his article described how a 1 metre rise in sea level would submerge an estimated 2.2m square kilometres of land, largely in Asia and displace around 145 million people at a global cost of $944 billion.

He also points out that while Laurentide ice sheet completely vanished at the end of the last ice age the Greenland ice sheet is more resistant to warming. He writes that,
"To what extent this dynamic response of the Laurentide ice sheet to past temperature change can be considered analagous to present and future reduction of the Greenland ice sheet remains unresolved but [the researchers'] work suggests that future reductions of the Greenland ice sheet on the order of 1 metre per century are not out of the question."