By using eleven years of data collected by satellites from the European Space Agency (ESA), European researchers have found that the ice sheet covering the interior of Greenland has gotten thicker at a rate of more than 6 centimeters per year. Another analysis published three months ago shows similar results for Antarctica. While the edges of the glaciers are melting, the interiors are getting thicker. And even if it looks strange for non-specialists, it is completely coherent with the theories about global warming. Increases in temperatures mean more moisture -- or snow -- at high elevations. But these effects should be reversed in a few hundred years and sea levels will increase by at least seven meters for Greenland's melting only.
First, here are some facts about the ice coverage of Greenland.
The ice sheet covering Earth's largest island of Greenland has an area of 1 833 900 square kilometres and an average thickness of 2.3 kilometres. It is the second largest concentration of frozen freshwater on Earth and if it were to melt completely global sea level would increase by up to seven metres.
And what will happen next?
The influx of freshwater into the North Atlantic from any increase in melting from the Greenland Ice Sheet could also weaken the Gulf Stream, potentially seriously impacting the climate of northern Europe and the wider world.
But it's still too early to know what might happen. In the mean time, below is a beautiful picture which will give you an idea of the ice movement in Greenland (Credit: Ben Lee, Harvard University).
So what have found these researchers with the help of the ESA satellites?
By combining tens of millions of data points from ERS-1 and ERS-2, the team determined spatial patterns of surface elevation variations and changes over an 11-year period.
The result is a mixed picture, with a net increase of 6.4 centimetres per year in the interior area above 1500 metres elevation. Below that altitude, the elevation-change rate is minus 2.0 cm per year, broadly matching reported thinning in the ice-sheet margins. The trend below 1500 metres however does not include the steeply-sloping marginal areas where current altimeter data are unusable.
So the thickness of the ice sheet in Greenland has increased of about 70 centimeters in 11 years. What does this mean for our environment if we think about global warming effects?
Modelling studies of the Greenland Ice Sheet mass balance under greenhouse global warming have shown that temperature increases up to about 3ºC lead to positive mass balance changes at high elevations – due to snow accumulation -- and negative at low elevations -- due to snow melt exceeding accumulation.
Such models agree with the new observational results. However after that threshold is reached, potentially within the next hundred years, losses from melting would exceed accumulation from increases in snowfall -- then the meltdown of the Greenland Ice Sheet would be on.
For more information, this recent research work has been published by the Science journal under the name "Recent Ice-Sheet Growth in the Interior of Greenland" on October 20, 2005. Here is a link to the abstract.
Sources: European Space Agency news release, November 4, 2005; and various web sites
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