Earth's glaciers and ice caps are shrinking

February 14, 2012

Earth’s glaciers and ice caps outside of the regions of Greenland and Antarctica are shedding roughly 150 billion tons of ice annually, according to a new study led by the University of Colorado Boulder.

The research effort is the first comprehensive satellite study of the contribution of the world’s melting glaciers and ice caps to global sea level rise and indicates they are adding roughly 0.4 millimeters annually, said CU-Boulder physics Professor John Wahr, who helped lead the study. The measurements are important because the melting of the world’s glaciers and ice caps, along with Greenland and Antarctica, pose the greatest threat to sea level increases in the future, Wahr said.

The researchers used satellite measurements taken with the Gravity Recovery and Climate Experiment, or GRACE, a joint effort of NASA and Germany, to calculate that the world’s glaciers and ice caps had lost about 148 billion tons, or about 39 cubic miles of ice annually from 2003 to 2010.  The total does not count the mass from individual glacier and ice caps on the fringes of the Greenland and Antarctic ice sheets -- roughly an additional 80 billion tons.

“This is the first time anyone has looked at all of the mass loss from all of Earth’s glaciers and ice caps with GRACE,” said Wahr.  “The Earth is losing an incredible amount of ice to the oceans annually, and these new results will help us answer important questions in terms of both sea rise and how the planet’s cold regions are responding to global change.”

Launched in 2002, two GRACE satellites whip around Earth in tandem 16 times a day at an altitude of about 300 miles, sensing subtle variations in Earth’s mass and gravitational pull. Separated by roughly 135 miles, the satellites measure changes in Earth’s gravity field caused by regional changes in the planet’s mass, including ice sheets, oceans and water stored in the soil and in underground aquifers

“The strength of GRACE is that it sees everything in the system,” said Wahr. “Even though we don’t have the resolution to look at individual glaciers, GRACE has proven to be an exceptional tool.”  Traditional estimates of Earth’s ice caps and glaciers have been made using ground-based measurements from relatively few glaciers to infer what all of the unmonitored glaciers around the world were doing, he said. Only a few hundred of the roughly 200,000 glaciers worldwide have been monitored for a decade or more.

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