Increase in West Antarctic Ice Sheet Melting Inevitable in 21st Century

There will be widespread melting of the West Antarctic ice shelves this century, even if the world were on track to achieve the most ambitious Paris Agreement climate targets, according to new research. The study, published in the journal Nature Climate Change, posits that the stability of the entire West Antarctic Ice Sheet will be threatened by future ocean warming at three times the rate previously observed last century, with mitigation of greenhouse gas emissions having little-to-no effect this century.

Just how much sea-level rise is already unavoidable and must be adapted to? And how much ice loss can still be controlled by reducing emissions? To shed light on these questions, the model-based study assessed ice-shelf melting under different future emissions scenarios and laid out key evidence to be used in crucial policy decisions.

Ice shelves—the floating extensions of glaciers and ice sheets—hold back the flow of land ice toward the ocean, slowing the rate of sea-level rise. If all the glaciers in the West Antarctic Ice Sheet were to melt into the ocean, global sea level would increase by 5.3 meters. As a result, scientists have paid great attention to the ice shelves that are currently restricting uncontrolled mass loss from Antarctica. Due to intense interactions with the surrounding Southern Ocean, where warm waters are melting the ice shelves from below, the Amundsen Sea region of West Antarctica is an area of particular concern.

Relying on an improved scientific model of complex processes, the researchers found no significant difference in the effect of ocean warming or ice-shelf melting between the Paris Agreement’s 1.5 ℃ and 2 ℃ warming scenarios. Even under 1.5 ℃ of global warming, the Amundsen Sea is projected to heat up three times faster in this century than in the last.

“Reducing emissions would likely have a positive impact after 2100. Before then, emissions mitigation can help to prevent the worst-case scenario [of melting], but further reductions have negligible impact. Ocean warming and ice-shelf melting are not very sensitive to the emissions scenario,” said Kaitlin Naughten, lead author and ocean modeler at the British Antarctic Survey, in an interview with GlacierHub.

Even if we were to mitigate greenhouse gas emissions now to avoid the worst-case scenario, the effect of the reduction would not be noticeable for a few decades, and by then damage to some glaciers may be irreversible, regardless of ocean warming.

The authors attribute intensified ocean warming to stronger circulation of ocean water masses over the continental shelf (the relatively shallow area of seabed around land masses), which transports greater volumes of warm water upwelled from the depths of the ocean onshore, toward the base of ice shelves.

Previous research attempting to project future melting from Antarctic ice shelves has often been unreliable due to limitations in the models used to make such predictions. This new study uses a regional ocean model of the Amundsen Sea that accounts for natural variability in the climate and corrects some inaccuracies to atmospheric and oceanic components used previously, increasing its ability to faithfully capture what is happening in our climate.

“Our study only used one model. In climate science, we like to use multiple models whenever possible to get a better idea of the uncertainty, but this takes a lot of time, staff and resources,” Naughten explained. “We hope that in the future more modeling groups will run similar experiments so that we have something to compare to.”

The authors also point out that while ocean melting of ice shelves is presently the leading cause of mass loss from West Antarctica, atmospheric processes may become more important in the future.

The new findings paint a grave picture for the state of the West Antarctic Ice Sheet. We may now have limited capacity to stop ice-shelf collapse in the region and prevent meters of global sea-level rise. Experts are warning that policy-makers should consider adaptation to sea-level rise a primary concern, as the window to safeguard the ice sheet from irreversible damage has probably now passed.

Antarctica’s climate has been subject to dramatic changes in 2023, as it recorded its lowest-ever winter sea ice extent in September. Aside from the effects of sea-level rise, changes to annual sea ice patterns are having alarming impacts on fragile Antarctic ecosystems.

This new research paints a more realistic picture for the fate of Antarctic ice shelves and highlights the necessity for continued mitigation of greenhouse gas emissions in order to avoid the worst-case ocean warming scenario, as well as the urgent need for prioritization of adaptation to global sea-level rise.