Already we have seen record summer melting in Greenland in 2010, and near record mass loss in 2011. According to NOAA the melt season in 2011 lasted up to 30 days longer than average and it affected 31 percent of the ice sheet surface, making 2011 one of just three years since 1979 where melt area exceeded 30 percent. Polar regions are warming much faster and to a greater degree than any other latitude on earth.
We estimate that the warming threshold leading to a monostable, essentially ice-free state is in the range of 0.8-3.2 °C, with a best estimate of 1.6 °C. By testing the ice sheet's ability to regrow after partial mass loss, we find that at least one intermediate equilibrium state is possible, though for sufficiently high initial temperature anomalies, total loss of the ice sheet becomes irreversible.
"The more we exceed the threshold, the faster it melts," says Alexander Robinson, lead-author of the study that has just been published in Nature Climate Change. If greenhouse-gas emissions continue on a business-as-usual approachm we could be looking at 8 degrees Celsius of global warming. This would result in 20 per cent of the ice sheet melting within 500 years and a complete loss in 2000 years, according to the study.
Most of the small island states that are vulnerable to rising sea levels have voiced strong concern at the 2°C temperature limit as being too high and will result in their countries being innundated. The Climate Vulnerable Countries'Forum in 2009 called for "ambitious emission reduction targets consistent with limiting global average surface warming to well below 1.5 degrees Celsius above preindustrial levels and long-term stabilization of atmospheric greenhouse gas concentrations at well below below 350 p.p.m."
- Alexander Robinson, Reinhard Calov & Andrey Ganopolski, Nature Climate Change, 11 March 2012 - Multistability and critical thresholds of the Greenland ice sheet (abstract) doi:10.1038/nclimate1449
- Potsdam Institute for Climate Impact Research (PIK) media release 11 March 2012 - Greenland ice sheet may melt completely with 1.6 degrees global warming
- Image - Greenland 2011 melt season anomaly from NOAA