Four meters of sea-level rise due to ice sheet collapse would be irreversible, study suggests

Ice loss from Antarctica's vast freshwater reservoir could threaten coastal communities and the global economy if the ice volume decreases by just a few per cent.

In a new study published in Communications Earth & Environment, researchers from academic institutions in Norway, UK and Germany have run model simulations through the glacial cycles over the last 800,000 years. During this period, the Earth’s climate has switched several times between cold ‘glacials’ and warmer ‘interglacials’. Some of these past interglacials were likely warmer than our present-day climate and give a picture of how the vast Antarctic Ice Sheet could respond to future warming.

– In the past 800,000 years, the Antarctic Ice Sheet has had two stable states that it has repeatedly tipped between. One, with the West Antarctic Ice Sheet in place, is the state we are currently in. The other state is where the West Antarctic Ice Sheet has collapsed, first author David Chandler from NORCE in Norway tells.

Tipping the West Antarctic Ice Sheet to the collapsed state, is controlled by the ocean temperature around Antarctica, because the heat needed to melt ice in Antarctica is supplied mostly by the ocean.

– As little as 0.25°C deep ocean warming above present-day can trigger the start of a collapse. This amount of warming is likely within the next few decades according to warming rates from recent observations close to Antarctica. Possible changes in ocean dynamics may even accelerate warming. A full collapse would eventually contribute to over four m sea-level rise on a global average, with some regional variability, Chandler says.

– With our present-day climate, the transition to the collapsed state will be slow, maybe 1,000 years. But it will likely be much faster if there is additional global warming, he adds.

Once the ice sheet has tipped to the collapsed state, reversal back to the stable present-day state would need several thousands of years of temperatures at or below pre-industrial conditions.

– It takes tens of thousands of years for an ice sheet to grow, but just decades to destabilise it by burning fossil fuels. Now we only have narrow window to act, said co-author Julius Garbe from the PIK.

– Once tipping has been triggered it is self-sustaining and seems very unlikely to be stopped before contributing to about four meters of sea-level rise. And this would be practically irreversible, Chandler added.

The research and simulations have been conducted by David Chandler and Petra Langebroek from NORCE and the Bjerknes Centre for Climate Research, Ronja Reese from Northumbria University, and Torsten Albrecht, Julius Garbe and Ricarda Winkelmann from the Potsdam Institute for Climate Impact Research .