Glaciers: The Biggest Losers


Though many folks have failed at their News Year's resolution to shed a few pounds, the Earth's glaciers and ice cap are having no trouble losing weight.

Every year, 148 billion tons (134 billion tonnes), or approximately 39 cubic miles (163 cubic kilometers), of ice melt from the world's glaciers. And that doesn't include the glaciers and ice packs on the fringes of the Greenland and Antarctic ice sheets. They melt another 80 billion tons of water into the ocean every year, making the total yearly melt approximately 230 billion tons, concluded a University of Colorado study published online today in the journal Nature.

The loss equates to about eight times the volume of Lake Erie between 2003 and 2010, said study co-leader, John Wahr, a physics professor at the University of Colorado at Boulder, in a press release.

"The total amount of ice lost to Earth's oceans from 2003 to 2010 would cover the entire United States in about 1 and one-half feet of water," Wahr said.

All that water adds roughly 0.4 millimeters (.0004 inches) annually. Total sea level rise from all land-based ice melt was approximately 1.5 millimeters (.0015 inches) per year or about 12 millimeters (.012 inches) from 2003 to 2010, said Wahr, but about half of that resulted from thermal expansion of ocean water due to a warming climate.

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The Gravity Recovery and Climate Experiment (GRACE) satellite system allowed measurement of the decreasing mass of all the world's glaciers and rise in sea levels. Previous studies relied on surface estimates of glacial melt from relatively few sources.

GRACE consists of two satellites racing around the Earth 16 times per day about 300 miles (483 kilometers) above the surface. The satellites measure tiny variations in the Earth's mass and gravitational pull.

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Roughly 135 miles (217 kilometers) separates the satellites, so a tug on one from Earth's gravity, even as small as a 1 micron (1/100th of a millimeter), pulls one satellite out of alignment with the other. The misalignment registers on the GRACE system's sensors as a variation in the planet's gravitational field.

Since weight equals mass multiplied by the acceleration of gravity, the data from the satellites can be used to translate the changes in gravity to estimate regional changes in the planet's mass, including ice sheets, sea levels and water stored in the soil and in underground aquifers. The mass calculations can then be converted into familiar weight measurements.

"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," Wahr said. "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."

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"What is still not clear is how these rates of melt may increase and how rapidly glaciers may shrink in the coming decades," said Tad Pfeffer, a professor in the University of Colorado at Boulder's civil, environmental and architectural engineering department, in a press release.

"That makes it hard to project into the future," Pfeffer said.

"One big question is how sea level rise is going to change in this century," Pfeffer said. "If we could understand the physics more completely and perfect numerical models to simulate all of the processes controlling sea level — especially glacier and ice sheet changes — we would have a much better means to make predictions. But we are not quite there yet."


View from the Alte Prager Hütte to the glacier Schlatenkees and the Großvenediger at Hohe Tauern, Alps, Austria. (Rafael Brix, Wikimedia Commons)

The Briksdal Glacier is a part of the Jostedal Glacier National Park. (sgm, Wikimedia Commons)

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