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Humans Overtake Ice Ages As Main Driver Of Glacier Melt

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"Humans Overtake Ice Ages As Main Driver Of Glacier Melt"

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The Aletsch Glacier in Switzerland is the largest valley glacier in the Alps.

The Aletsch Glacier in Switzerland is the largest valley glacier in the Alps.

CREDIT: flickr/NASA Goddard Space Flight Center

Glaciers have been retreating globally since the end of the “Little Ice Age” in the mid-19th century, but now humans are the primary culprits.

A new study has confirmed what many who follow the science already assumed: that human-caused greenhouse gas emissions are leading glaciers to melt faster than they otherwise would. The study, published Thursday in the journal Science, found that between 1851 and 2010 humans were responsible for only about a quarter of global loss of glacier mass. However this ratio has soared over the last two decades, with humans now accounting for around 69 percent of the melting.

“Typically, it takes glaciers decades or centuries to adjust to climate changes,” Ben Marzeion, lead author of the paper and a a climate scientist at the University of Innsbruck in Austria, said in a statement. “In the 19th and first half of 20th century we observed that glacier mass loss attributable to human activity is hardly noticeable but since then has steadily increased.”

Even as melting glaciers represent some of the most emblematic and visually stunning imagery associated with climate change, they are slow to respond to changes in climate. Because of this complex physical process, it will be decades before humans can start to see future impacts from the decisions made today around climate change mitigation.

“Over the next 50 years or so there is hardly anything we can do about it,” Marzeion said. “Whether we really limit the greenhouse gas emissions or not, the glaciers are going to continue to melt.”

 

Glacier mass balance (snow gain minus melt loss) from 1980 through 2011. Bars indicate positive (above the 0 line) and negative (below the 0 line) glacier mass balances each year, and the red line shows the cumulative annual balance. Only three years—1983, 1987, and 1989—experienced net gains. All other years had negative mass balances, with losses getting larger in more recent years.

Glacier mass balance (snow gain minus melt loss) from 1980 through 2011. Bars indicate positive (above the 0 line) and negative (below the 0 line) glacier mass balances each year, and the red line shows the cumulative annual balance. Only three years—1983, 1987, and 1989—experienced net gains. All other years had negative mass balances, with losses getting larger in more recent years.

CREDIT: climate.gov

 

However, in the long term, the fate of the glaciers rests firmly in the control of humans, Marzeion added. If strong mitigation measures are taken now, glaciers may recede about another 40 percent by 2100. However, if little action is taken and GHGs continue to rise sharply, 70 percent of global glacier mass could enter the rivers, seas, and oceans of the world by 2100. And the remaining 30 percent likely wouldn’t be far behind. The world’s glaciers contain enough water to raise sea levels by 16 inches, according to the United Nations.

This study is the first to quantify the established theory in the climate community that as humans warm the climate, associated glacier melt will lag as they are slow to respond to the warming. To reach these results, the scientists used climate computer modeling to map glaciers everywhere in the world outside of Antarctica. They studied how glacier melting would occur with and without human-generated GHGs and factored in natural variables such as solar variability and volcanic eruption.

Another study this week focused on Antarctica’s ice discharge, which has been shown to be entering an irreversible decline in some areas. Led by the Potsdam Institute for Climate Impact Research in Germany, the study found that ice melt from Antarctica could raise seas levels by as much as 14.6 inches this century if GHG emissions continue to steadily mount. This is more than was previously thought. The Antarctic ice sheet contains enough water to raise sea levels by over 190 feet, though even with the current elevated levels of GHGs this would take thousands of years.

“If greenhouse gases continue to rise as before, ice discharge from Antarctica could raise the global ocean by an additional one to 37 centimeters (14.5 inches) in this century already,” lead author Anders Levermann, of the Potsdam Institute for Climate Impact Research, said in a statement. “Now this is a big range — which is exactly why we call it a risk: Science needs to be clear about the uncertainty, so that decision makers at the coast and in coastal megacities like Shanghai or New York can consider the potential implications in their planning processes.”

Even if humans limit global warming to 2°C, a common target to avoid catastrophic damage, the contribution of Antarctica to global sea level rise covers a range of zero to nine inches.

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