Extensive melting of West Antarctic ice sheet now looks unavoidable

The ice shelves that hold back the West Antarctic ice sheet will be melted by warming seawater, even in the unlikely event that the world achieves its 1.5°C climate goal, a computer model of the ocean suggests.

The study doesn’t forecast how much sea level rise this will result in, but concludes that policy-makers need to prepare for several metres of sea level rise over the coming centuries.

“There will be some impacts of climate change – and it looks like this could be one of them – that we cannot stop, that we have to adapt to,” says Kaitlin Naughten at the British Antarctic Survey.

In its 2021 report, the Intergovernmental Panel on Climate Change (IPCC) projected that, in moderate emissions scenarios, sea level would rise between 0.5 and 1 metre by 2100. Naughten says her team’s findings suggest that the sea level will rise by more than the IPCC’s projections, though she cannot say by how much.

Around Antarctica, the surface waters are about -1.5°C (29°F), but the water several hundred metres down is around 1°C (34°F) – warm enough to melt ice.

Based on a model of the Amundsen Sea off West Antarctica, Naughten and her colleagues predict that changing currents will bring this deeper water closer to the surface, resulting in the melting of the floating ice shelves.

The disappearance of such floating ice doesn’t raise sea level directly, but when ice shelves are lost, the flow of ice from land into the sea speeds up. What’s more, much of the West Antarctic ice sheet rests on rock that is below sea level.

This ice will be exposed to the warming ocean water when the ice shelves are lost, melting its base and causing the collapse of the ice above sea level. This “cliff collapse” could lead to the rapid retreat of the ice.

The model shows that the warming of the Amundsen Sea will proceed at much the same rate over the next half century in four emissions scenarios, ranging from best case to worst case. It is only around 2080 that substantial differences in ocean warming begin to emerge.

But cutting emissions as fast as possible remains crucial, says Naughten. “Even if this particular impact is unavoidable, the melting of the West Antarctic ice sheet is only one impact of climate change.”

For instance, we can still avoid the loss of the East Antarctic ice sheet, which holds 10 times as much ice as the West Antarctic one, she says.

“It is a very good modelling exercise because it is based on a high-resolution model,” says Eric Rignot at the University of California, Irvine.

Ed Gasson at the University of Exeter in the UK thinks the study is right that we are on course for the collapse of the West Antarctic ice sheet. “I don’t think it’s that surprising that, given the current concentration of atmospheric greenhouse gases and given what we know from palaeoclimate studies, the West Antarctic ice sheet may eventually collapse,” says Gasson. “How rapidly that may occur is still a real unknown.”

However, Rignot and Gasson both point out that the study looks only at the ocean and doesn’t include atmospheric processes. Rignot says other studies suggest a rapid cut in emissions would change the winds around Antarctica and thus change ocean currents.

“I do not agree that the time to affect this collapse has completely passed,” says Rignot. “If we curb our greenhouse gas emissions very aggressively and – in addition – are able to sequester atmospheric carbon back in the ground, to go back to concentrations reached in the earlier part of the 20th century, then I do believe there is a chance to slow down the retreat.”

At present, however, global greenhouse gas emissions are still rising rather than falling. Meanwhile, around the world, development continues in many coastal areas and in cities that will be impractical to protect from several metres of sea level rise.