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Greenland ice sheet vulnerable to warming

2012-03-12 12:20

Paris - The Greenland ice sheet is more sensitive to global warming than thought, for just a relatively small - but very long term - temperature rise would melt it completely, according to a study published on Sunday.

Previous research has suggested it would need warming of at least 3.1°C above pre-industrial levels, in a range of 1.9°C - 5.1°C, to totally melt the ice sheet.

But new estimates, published in the journal Nature Climate Change, put the threshold at 1.6°C, in a range of 0.8° - 3.2°C, although this would have to be sustained for tens of thousands of years.

Greenland is second to Antarctica as the biggest source of locked-up water on land.

If it melted completely, this would drive up sea levels by 7.2m, swamping deltas and low-lying islands.

If global warming were limited to 2°C, a target enshrined in the UN climate-change negotiations, complete melting would happen on a timescale of 50 000 years, according to the study.

Current carbon emissions, though, place warming far beyond this objective. If they were unchecked, a fifth of the ice sheet would melt within 500 years and all would be gone within 2 000 years, the study says.

Stability


The probe is authored by scientists from the Potsdam Institute for Climate Impact Research (PIK) and the Universidad Complutense de Madrid.

They say that the risk of total loss may seem remote, given the immense timescale.

But they also warn that their findings challenge many assumptions about the ice sheet's stability in response to long-term warming.

Earth's atmosphere has already warmed by 0.8°C since the start of the Industrial Revolution in the mid-18th century, and carbon dioxide (CO2) that is being emitted today will linger for centuries to come.

The ice sheet is vulnerable to a kind of vicious circle, also known as a positive feedback, that cranks up the melt, according to the paper.

Reaching over 3 000m thick in some places, the ice sheet today benefits from the protective effect of higher, cooler altitudes.

But when it melts, the surface comes down to lower altitudes which have higher temperatures, and this accelerates the cooling, the computer models show.

In addition, patches of land that become exposed by ice absorb solar radiation because they are darker and do not reflect the light. As they warm up, they in turn help melt the ice nearby.

"Our study shows that under certain conditions the melting of the Greenland ice sheet becomes irreversible. This supports the notion that the ice sheet is a tipping element in the Earth system," said PIK researcher Andrey Ganopolski.

"If the global temperature significantly overshoots the threshold for a long time, the ice will continue melting and not re-grow - even if the climate would, after many thousand years, return to its pre-industrial state."

Comments
  • S - 2012-03-12 13:02

    Greenland had significantly less ice coverage in recent human history - hence the name _Green_land. The name was given by the Viking Erik the Red about 1000 years ago. During the Little Ice Age, Greenland froze over again and drove the Nordic settlers out. It's all natural. Humans do not cause the warming.

  • Sean - 2012-03-12 14:00

    This Global warming is comming along quite nicely. Soon we will be able to plant maize and wheat across the vast plains of Greenland, Siberia and Canada, solving world food shortages. I cannot understand why some people want to keep these vast areas under ice and uninhabitable.

  • Horst - 2012-03-12 16:30

    Well, I visited some of the glaciers in Southern Greenland in 1998. Of the three that I have pictures off I had a look at Google Earth (2010/2012 images) and guess what those glaciers are certainly not retreating. So what is going on here?

      Peter - 2012-03-12 22:18

      Have you visited Athabasca? I climbed up past ever-closer time-markers that illustrate the glacier's rapidly increasing retreat. Half North America's water reserve lies in the Canadian Ice Sheild, so let's not kid ourselves.

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