Original URL: http://www.theregister.co.uk/2012/03/11/greenland_ice_sheet_vulnerable/

Greenland melt threshold lower than thought

Ice could disappear with half as much warming: study

By Richard Chirgwin

Posted in Science, 11th March 2012 23:30 GMT

Spanish and German scientists have have alarmed the international environmental community with modeling suggesting that Greenland’s ice sheets could disappear at lower temperatures than previously thought.

The study was conducted by Spain’s Universidad Complutense de Madrid and the Potsdam Institute for Climate Impact Research in Germany. They found that rather than a best-estimate temperature rise (compared to pre-industrial levels) of 3.1°C, Greenland’s ice would eventually succumb to a rise of as little as 1.6°C.

The good news is that complete loss of the ice sheet is, even under the Spanish-German model, about 2,000 years distant. However, they say, this is considerably faster than has happened before on Earth, and is more than an order of magnitude quicker than would happen if warming were contained.

If temperatures are contained to within 2°C of pre-industrial levels, the ice sheet would last another 50,000 years, the authors say.

According to Reuters, the research, published in the journal Nature Science Change, suggests scientists have been too optimistic in estimating the temperature needed to trigger substantial ice loss in Greenland.

“Our study shows that a temperature threshold for melting the (ice sheet) exists and that this threshold has been overestimated until now,” the paper states (abstract here).

The temperature in question is that at which the mass balance of Greenland’s surface ice “turns negative” – in other words, its summer melt is faster than its winter replenishment.

Using a “fully coupled model” the researchers suggest that while “one intermediate equilibrium state is possible … for sufficiently high initial temperature anomalies, total loss of the ice sheet becomes irreversible”.

In other words, while commendably avoiding the emotive term “tipping point”, the researchers do suggest that such a state exists. It’s feasible, in their study, that a point exists where even a reduction in temperatures wouldn’t reverse the loss of the ice sheet.

Both the previous estimates and the new estimate have considerable error bars: the former model for Greenland ice loss fell between 1.9 and 5.1°C, while the new model puts the maximum range between 0.8 and 3.2°C.

“The timescale of melt depends strongly on the magnitude and duration above this critical threshold,” the abstract says. ®