this is not what one would call a rapid collapse — Alexander Robinson

The Greenland ice sheet is more vulnerable to global warming than thought and could melt completely with just a 2.8-degree F rise, German researchers say.

The temperature threshold for the complete melting of the ice sheet completely is in the range of 1.4 degrees to 5.6 degrees, with 2.8 degrees above pre-industrial levels the best estimate, scientists at the Potsdam Institute for Climate Impact Research reported Sunday.

Climatologists have already observed the lower limit of 0.8 degrees of warming, the said.

"The more we exceed the threshold, the faster it melts," Alexander Robinson, lead-author of the study published in Nature Climate Change, said.

With ongoing greenhouse-gas emissions, humanity might be looking at an eventual 14 degrees F of global warming, which could result in one fifth of the ice sheet melting within 500 years and a complete loss in 2000 years, researchers said.

"This is not what one would call a rapid collapse," Robinson said. "However, compared to what has happened in our planet's history, it is fast. And we might already be approaching the critical threshold."

Substantial melting of Greenland ice could contribute to long-term sea-level rise of several yards with impact on the lives of millions of people, the researchers say.

"Our study shows that under certain conditions the melting of the Greenland ice sheet becomes irreversible," team-leader Andrey Ganopolski at the Potsdam institute said.

"This supports the notion that the ice sheet is a tipping element in the Earth system."

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