Critical tipping points determined in Greenland Ice Sheet melting beyond which irreversible changes expected

A new model using simulations to study the melting of Greenland Ice Sheet has determined two critical tipping points, in terms of carbon emissions, beyond each of which irreversible melting is expected to occur, according to a new study.

Releasing 1000 gigatonnes of carbon would cause the southern portion of the ice to melt, scientists said in the study.

They further said that releasing 2500 gigatonnes of carbon meant a permanent loss of nearly the entire ice sheet.

Having emitted about 500 gigatonnes of carbon, we're about halfway to the first tipping point, they said in the study published in the journal Geophysical Research Letters.

The Greenland Ice Sheet covers 1.7 million square kilometers in the Arctic. If it melts entirely, global sea level would rise about 7 metres, but scientists are not sure how quickly the ice sheet could melt.

''The first tipping point is not far from today's climate conditions, so we're in danger of crossing it,'' said Dennis Honing, lead researcher and a climate scientist at the Potsdam Institute for Climate Impact Research, Germany.

''Once we start sliding, we will fall off this cliff and cannot climb back up,'' said Honing.

The Greenland Ice Sheet is known to already melt at a rate of 255 gigatonnes of ice each year, much of which happens in the southern part of the ice sheet.

The scientists said it is hard to predict how the ice sheet will respond to different climate and carbon emissions scenarios, owing to the complexity in factors such as air and water temperature, ocean currents, precipitation and others, all of which determine the rate and location of ice melting.

Previous research has identified global warming between 1 and 3 degrees Celsius to be the threshold beyond which the Greenland Ice Sheet will melt irreversibly.

To comprehensively model the ice sheet's response to climate over time, Honing's study used a complex model of the whole Earth system, which included key climate feedback processes, coupled with ice sheet behaviour model.

Using simulations, the team determined equilibrium states, where ice loss would equal ice gain. This was followed by running 20,000-year-long simulations with carbon emissions ranging from 0 to 4000 gigatonnes of carbon.

It is from here that the scientists derived the two aforementioned tipping points.

As the ice sheet melts, its surface will be at lower elevations, exposing it to warmer air temperatures, which accelerate melting, making it drop and warm further.

For this feedback loop to become effective, the scientists said that global air temperatures would have to remain elevated for at least hundreds of years.

However, once the threshold is crossed, they said, even pre-industrial levels of atmospheric carbon dioxide would not be enough to allow the ice sheet to regrow substantially.

''We cannot continue carbon emissions at the same rate for much longer without risking crossing the tipping points,'' Honing said.

''Most of the ice sheet melting won't occur in the next decade, but it won't be too long before we will not be able to work against it anymore,'' Honing said.

(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)