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Scientists who carried out the first
comprehensive analysis of changing speeds of the glaciers on the
world's largest island were shocked to discover that many have
doubled in speed within the past decade.
Warmer temperatures are "lubricating" the
glaciers and have driven a 150 per cent increase in the amount
of ice they are delivering to the ocean between 1996 and last
year. The latitude at which this is happening is moving north.
The researchers fear that as a result current
estimates that sea levels will rise by up to 90cms during the
21st century could underestimate the problem.
While there have been previous isolated reports
of particular glaciers speeding up, the research presented
yesterday at the American Association for the Advancement of
Science conference in St Louis is the first detailed study
showing the effect is widespread across Greenland.
Eric Rignot, of Nasa's Jet Propulsion
Laboratory at the California Institute of Technology in
Pasadena, the leading author of the study, said: "Climate change
can work in different ways, but generally speaking, if you warm
up the ice sheet, the glacier will flow faster.
"The southern half of Greenland is reacting to
what we think is climate warming. The northern half is waiting
but I don't think it is going to take long. If more glaciers
accelerate farther north, especially along the west coast, the
mass loss from Greenland will continue to increase well above
predictions."
The Intergovernmental Panel on Climate Change
has estimated that global sea levels will increase by 10-90cms
over the next century. Last century they rose by 10-20cm.
Previously models of the melting of the
Greenland ice sheet have been based mainly on airborne laser
altimetry and have suggested that while the interior is
reasonably stable, the periphery was thinning, especially in
areas where glaciers meet the sea.
Dr Rignot and colleagues set out to obtain
accurate measurements to help to build a clearer picture of
Greenland's current and future contribution to rising sea
levels. They collected satellite data on the speeds of 27
glaciers and made estimates for two others.
The velocities of several large glaciers had
doubled in recent years to 12km per year, making them among the
fastest flowing in the world.
The scientists found that warmer air
temperatures have increased the overall shrinkage of the
Greenland ice sheet from 91 cubic km per year in 1996 to 138
cubic km per year in 2000 and to 224 cubic km per year in 2005.
About two-thirds of this was caused by the
dumping of ice in the Atlantic by glaciers and so the ice loss
attributable to glacier flow grew by 150 per cent from 60 cubic
km a decade ago to 150 cubic km last year.
On this basis Dr Rignot, whose work is
published in Science, concluded that Greenland's contribution to
rising global sea levels increased from around 0.23mm per year
in 1996 to around 0.57mm per year in 2005.
The Greenland ice sheet is 1.7 million sq km -
a little smaller than Mexico - and three kilometres thick. If it
melted completely sea levels would rise by seven metres.
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