Thread by @kaitlinnaughten

We’ve spent the last few years modelling the future of the Amundsen Sea in West Antarctica, and I regret to inform you that it’s not good news. nature.com/articles/s4155…

The Amundsen Sea sector is the fastest-changing region of the Antarctic Ice Sheet, and the most vulnerable given the geometry of the bedrock beneath it. But because ice shelf melting by the ocean is hard to model, we have very few projections of how it could change in the future.

We simulated a range of future scenarios using a regional ocean model with ice shelves. We wanted to know: how much control do we still have over ice shelf melting? How much can still be prevented by reducing fossil fuel emissions, and how much is now committed?

Unfortunately, even the best-case scenario was still very bad. All scenarios showed a 3x increase in ocean warming and ice shelf melting trends over the 21st century.

There was little to no difference between the scenarios. The Paris Agreement 1.5°C scenario (wildly ambitious) and RCP 4.5 (roughly in line with current pledges) were statistically indistinguishable.

The worst-case scenario (RCP 8.5) showed faster ocean warming than the others, but only after 2045. This is a crucial few decades for the glaciers in which we have no control over accelerating ocean warming.

Climate change is the cause of these simulated trends - but the main determinant of the precise amount of warming is climate variability, not the emissions scenario. The trend can vary by a factor of 2 depending on the timing of natural, unpredictable events like El Niño.

We didn’t have a coupled ice sheet model, so cannot quantify the sea level rise implications, but they are unlikely to be good. The IPCC projected <=1 metre of sea level rise by 2100, and perhaps higher if ice-ocean interactions take off - exactly the process we were studying.

What we can do is look at the spatial distribution of melting and infer its importance for sea level rise. We find increased melting in all regions of the ice shelves, including those with the highest buttressing (stabilising the inland ice sheet).

Look closely - the additional melting in the worst-case scenario (RCP 8.5) is mostly among the ice shelves with lower buttressing. So the additional losses, which we can still prevent, are mostly in the regions that don’t matter too much for sea level rise.

So, it’s pretty bad news. But I would hate for people to read this story and think “we should give up on climate action, we’re all doomed anyway”. We must remember that West Antarctica is just one cause of sea level rise, and sea level rise is just one impact of climate change.

East Antarctica contains about ten times as much ice as the WAIS, and we think it’s still stable as long as emissions don’t rise too much further. This is to say nothing of all of the other impacts of climate change which we could still prevent.

Also, 2100 is just the beginning of the story. We see ice shelf melting beginning to flatten out towards the end of the century in the Paris Agreement scenarios. So we likely still have control over the longer-term - into the 22nd century and beyond.

Very few people reading this will still be around after 2100, but that doesn’t mean we don’t have a responsibility to the generations alive then. We need to shift our focus to the longer term.

In the meantime, we should think more seriously about adaptation. Some amount of sea level rise is inevitable - in fact, it’s already happening.

This study is the most comprehensive set of future projections of Amundsen Sea ice shelf melting to date. Huge thanks to my co-authors Paul Holland and Jan De Rydt, and the media teams at @BAS_News and @NatureClimate for spreading the word.