Edge of Ekstroem shelf ice, December 2002 (Polarstern expedition ANT-XX/2). Credit: Hannes Grobe (CC Share-Alike 2.5)
Between 2003 and 2010, the Earth lost 4.3 trillion tons (1,000 cubic miles) of ice mass — enough to raise global sea levels about 0.5 inches (12 mm) or cover an area the size of the U.S. with 1.5 feet (0.5 m) of water — according to a new study published February 8 in the online journal Nature.
Average yearly change in mass (in cm.) of water during 2003-2010, for just Greenland and Antarctica and their peripheral glaciers and ice caps. Blue represents ice mass loss, while red represents ice mass gain. Source: NASA/JPL-Caltech/University of Colorado
The comprehensive study, conducted by researchers at the University of Colorado at Boulder using measurements from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE), is the first to use satellite data to survey the melting of land ice globally, including losses from Earth’s glaciers and ice caps, Greenland and Antarctica.
The new study indicates that approximately three-fourths of global ice loss occurred in Greenland, Antarctica and their peripheral ice caps and glaciers.
However, annual losses in the high Asian mountain ranges, including the Himalaya, Pamir and Tien Shan, were estimated to be about 4 billion tons – far less than the 50 billion tons suggested by some previous, ground-based studies.
Average yearly change in mass (in cm.) of water during 2003-2010, for all the world’s glaciers and ice caps (excluding Greenland and Antarctica), and for the plains across northern India and adjacent regions. Blue represents ice mass loss, while red represents ice mass gain. Source: NASA/JPL-Caltech/University of Colorado
“One possible explanation is that previous estimates were based on measurements taken primarily from some of the lower, more accessible glaciers in Asia and extrapolated to infer the behavior of higher glaciers,” said University of Colorado Boulder physics professor John Wahr, who helped lead the study. “But unlike the lower glaciers, most of the high glaciers are located in very cold environments and require greater amounts of atmospheric warming before local temperatures rise enough to cause significant melting. This makes it difficult to use low-elevation, ground-based measurements to estimate results from the entire system.”
“This study finds that the world’s small glaciers and ice caps in places like Alaska, South America and the Himalayas contribute about 0.02 inches per year to sea level rise,” said Tom Wagner, cryosphere program scientist at NASA. “While this is lower than previous estimates, it confirms that ice is being lost from around the globe, with just a few areas in precarious balance. The results sharpen our view of land-ice melting, which poses the biggest, most threatening factor in future sea level rise.”
GRACE measurements are derived from twin satellites, travelling in the same orbit and approximately 137 miles (220 kilometers) apart. As the satellites pass over the Earth, they are affected by minute changes in gravitational pull from variations in Earth’s mass. These differences cause one spacecraft to travel slightly faster than the other, increasing the distance between them — which is measured to 1/100 the width of a human hair.
