Ice caps not shrinking as much as once thought, new data show

Through most of the last decade, mountain glaciers and ice caps around the globe collectively lost 148 billion tons of ice a year, according to new satellite measurements.

Although significant, the rate is some 30 percent lower than previous studies have suggested, according to the scientists performing the analysis.

Those losses, which do not include losses from thick ice sheets covering Greenland and Antarctica, contributed about 0.41 millimeters a year to sea-level rise, according to the study.

Mountain glaciers and ice caps represent a major source of fresh water for hundreds of millions of people worldwide.

“The Earth is losing an incredible amount of ice to the oceans annually,” notes John Wahr, a physicist at the University of Colorado at Boulder and a member of the team reporting the results in Thursday's issue of the journal Nature.

The losses coincide with the global average temperatures that turned the first decade of the 21st century into the warmest decade in the instrument record.

Most atmospheric scientists attribute the climate's current long-term warming trend at least in part to a build-up of greenhouse gases in the atmosphere, mainly carbon-dioxide. The buildup of CO2 comes from burning fossil fuels, as well as from land-use changes.

“These new results will help us answer important questions in terms of both sea-level rise and how the planet's cold regions are responding to global change,” Dr. Wahr said in a prepared statement.

Retreating mountain glaciers have become among the most prominent icons of global warming.

“The good news here is that they are not losing mass as quickly as we thought,” says Ian Howat, a glacier and ice-sheet specialist at Ohio State University's Byrd Polar Research Center in Columbus, Ohio. “The bad news is that while we're not losing mass from ice caps and glaciers as quickly, we're still not gaining it anywhere.”

Global figures during the 2003-2010 study period mask wide regional differences. The research team, led by Thomas Jacob, currently with France's Bureau de Recherches Géologiques et Minières, the French counterpart to the US Geological Survey, found the most significant rates of decline in Alaska, the Canadian Arctic, Iceland, and Patagonia.

Why have the global loss rates fallen? Previous studies relied largely on measurements taken on site and by aircraft at a relative handful of the world's 200,000 glaciers and ice caps. Scientists used those measurements to estimate changes over an entire mountain range.

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