MELTING ICE-SHEETS DOMINATE RISING SEA

The Greenland and Antarctic ice sheets are losing mass at an accelerating rate, according to a new NASA-funded satellite study, the longest study of changes in polar ice sheet mass. It suggests that they are overtaking the loss from mountain glaciers and ice-caps to become the dominant contributor to global sea-level rise, much sooner than model forecasts have predicted.

In 2006, a year in which comparable results for the loss from mountain glaciers and ice caps are available from a separate study, the Greenland and Antarctic ice-sheets lost a total average of 475 gigatonnes a year, enough to raise global sea-level an average of 1.3 millimeters a year

The pace at which the polar ice sheets are losing mass was found to be accelerating rapidly. Each year over the course of the study, the two ice-sheets lost a combined average of 36.3 gigatonnes more than they had the year before. In comparison, the 2006 study of mountain glaciers and ice caps estimated their loss at 402 gigatonnes a year on average, with an acceleration rate a third that of the ice-sheets.

'That ice-sheets will dominate future sea-level rise is not surprising -- they hold a lot more ice than mountain glaciers,' said lead author Eric Rignot, of NASA's Jet Propulsion Laboratory, Pasadena, California, and the University of California, Irvine. 'What is surprising is this increased contribution by the ice-sheets is already happening. If present trends continue, sea-level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007.'

The authors conclude that if the rate at which the ice-sheets are now melting continues, the world's oceans would be 15 centimetres higher by 2050. When that is added to the predicted contribution of 8cms from glacial ice caps and 9cms from thermal-expansion, the total could reach 32cms.

Full report in ScienceDaily.