A new computer simulation by scientists at Germany's Potsdam Institute for Climate Impact Research (PIK) and the Universidad Computense de Madrid has calculated that Greenland's ice is likely to be more vulnerable to global warming than previously assumed.

The study, published in Nature Climate Change, said warming of 1.6 degrees Celsius is likely to be enough to tip Greenland into an irreversible spiral of melting.

Though the process would take centuries to complete, Greenland's sensitivity to warming is of great concern to climate scientists as it stores enough ice to raise sea levels several meters.

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

The scientist said 1.6 degrees above pre-industrial levels was the most likely point in a range between 0.8 degrees and 3.2 degrees of warming.

The earth is already estimated to have warmed by about 0.8 degrees since the industrial revolution.

Faster than expected

Nearly 85 percent of Greenland is covered in ice.

With more than 1.7 million square kilometers (656,000 square miles), the island composes the largest fresh water ice sheet in the Northern Hemisphere.

Previous models showed a global warming threshold of 3.1 degrees Celsius as the best estimate at which Greenland would melt.

The new estimate effectively slashes the threshold in half.

This means that even a rise of 2 degrees Celsius, which the Intergovernmental Panel on Climate Change (IPCC) has deemed the maximum safe level, might have devastating effects on Greenland's ice.

The Greenland study adds to science that suggests the IPCC's forecasts for sea level rise may be too conservative.

A report commissioned by the Arctic Council warned last year that Greenland's ice was melting at a much faster rate than previously estimated.

In 2007, the IPCC's last assessment report estimated that global average sea level would rise by 18 to 59 centimeters by the end of this century.

However, the scenario didn't include sufficient data for the Arctic, which is why scientists at PIK and elsewhere say the IPCC's projections will prove much too low.

Better model

The PIK study is based on a new simulation of the Greenland ice sheet and the regional climate.

The simulation also factors in "feedback effects." For instance, it considers that changes in snowfall and melt as a result of global warming will lead to a further rise in temperature and thus to more global warming.

The white ice and snow sheets reflect a lot of solar radiation back into space, but as ice cover shrinks, the earth will absorb more radiation, encouraging more warming.

According to the scientists, the computer simulation was able to correctly calculate both today's observed ice sheets and its evolution over previous glacial cycles.

They were then able to verify results by comparing them with previous climate data. That's why the scientists regard their estimates of Greenland temperature threshold as more reliable than previous studies which couldn't factor in feedback effects.

Runaway melting

If today's greenhouse gas emissions were to continue at today's pace, Alexander Robinson said the earth could warm by as much as 8 degrees Celsius.

In 500 years time, this level of warming would result in one fifth of the ice sheet melting, the study found. In 2000 years, the ice sheet would be completely gone.

The scientists warn that in the absence of action to tackle carbon emissions, these changes may soon be locked in.

"Under certain conditions, the melting of the Greenland ice sheets becomes irreversible," PIK's team leader Andrey Ganopolski said. "This supports the notion that the ice sheet is a tipping element in the Earth system."

If the global temperature significantly exceeds the threshold for a long time, "the ice will continue melting and not regrow - even if the climate would, after many thousand years return to its preindustrial state," Ganopolski said.

Author: Irene Quaile /las, sst
Editor: Nathan Witkop