Greenland’s Ice Sheet might be close to first tipping point

“Once we have emitted more than circa 1,000 gigatons carbon in total, we won’t be able to stop the southern part of the Greenland Ice Sheet to melt entirely in the long term, even if future generations would entirely stop emitting carbon then. This melting would cause a sea level rise by about 1.8 metres, implying that whole regions would become flooded and potentially uninhabitable,” states Dennis Höning, scientist at the Potsdam Institute for Climate Impact Research (PIK) and lead author of the study published in the journal Geophysical Research Letters. “As about 500 gigatons of carbon have already been emitted, the opportunity to avoid crossing this critical threshold is gradually diminishing.”

Greenland Ice Sheet: two possible tipping points

The second possible tipping point would arrive once humanity would cumulatively emit approximately 2,500 gigatons of carbon in total, according to the scientists. In consequence, the whole Greenland Ice Sheet would eventually melt and the sea level rise would rise by about 7 meters. While this melting would take hundreds or thousands of years, it would be difficult for the ice to grow back. As the Ice sheet melts, reducing its elevation, it would naturally be exposed to warmer temperatures regardless of whether we slow or eventually halt emissions. An Ice sheet continually exposed at lowering elevations can no longer grow or regenerate.

To find out where the tipping points of the Greenland Ice Sheet are and for which cumulative emissions they will be crossed, the researchers run a complex model of the whole Earth system. First, they studied equilibrium conditions of the ice sheet to determine the critical climate conditions at which the system would approach a new state. Then, they combined these results with model runs for 20 thousand years and anthropogenic emission scenarios from 0 to 4000 gigatons of carbon to see at which cumulative emissions tipping would occur.

“We cannot continue to emit carbon emissions at the same rate for much longer without risking crossing at least the first tipping point,” Höning concludes. “Most of the ice sheet melting won’t occur in the next decades, but it won’t be too long before we will not be able to work against it anymore.”