If all of Antarctica were to melt, global sea level rise could rise about 58m. Some of this, we now know, is unavoidable, even without further emissions–and if we succeed in keeping global temperatures under 1.5C.

As global temperatures continue to rise, it is essential to determine how much sea level rise is already locked-in, and what adaptations may be necessary under different emissions pathways.

A new study in Nature by researchers at the British Antarctic Survey and Northumbria University, looks at committed melting of the West Antarctic Ice Sheet (WAIS). This study is released on the back of a record-low sea ice extent in Antarctica, during which an area the size of Mongolia failed to freeze.

The main driver of this committed melt stems from the warming waters of the Amundsen Sea off the WAIS, which holds the equivalent of 5.3m of sea level rise. The WAIS largely comprises glaciers that are grounded beneath the ocean–meaning that warm water is melting them from underneath.

The researchers simulated how future warming in the Amundsen Sea could affect ice shelves in West Antarctica. They show that the Amundsen Sea has become exponentially warmer in recent decades, and the trajectory of that warming is unlikely to change in this century, even if all emissions were cut. Thus, the WAIS will continue to melt from within.

Floating ice shelves play an important role in holding back the ice sheet on land and their thinning causes increased flow of ice into the ocean, raising sea levels.

The new model simulations suggest that we are already committed to rapid ocean warming in the Antarctic over the 21st century, and the irreversible collapse of the West Antarctic Ice Sheet is likely, even if we meet our most ambitious climate goal and stay under 1.5°C.

Committed melt in both poles can only be a driver of more intense action to mitigate further melt. With each centimetre of sea level rise, the effects become more deadly. We still have the opportunity to get our emissions on track and prevent more devastation.

COP28 must acknowledge the global risks stemming from polar melt, and, in particular, the wide-reaching impacts of sea level rise on our food systems, cities and extreme weather.

Although achieving our emissions targets can help to slow the rate of sea level rise and avoid the collapse of the East Antarctic Ice Sheet, policymakers should be preparing for multi-metre sea level rise, now also amplified by locked-in sea-level rise from melting Greenland ice.

Read more about Greenland locked in sea level rise HERE.

Read more about the global risks of sea level rise HERE.