We’ve “lost control” of West Antarctic melting

The melting of the West Antarctic Ice Sheet may now be “locked in,” according to a new analysis.

Previous research has estimated that complete collapse of the sheet will cause about 5m of global sea level rise over several centuries.

Now, a study published in Nature Climate Change has found that ocean warming triggering this collapse is inevitable, even if the world meets the most ambitious Paris Agreement target of 1.5°C of warming.

The West Antarctic Ice Sheet is a small but quickly-melting portion of the Antarctic ice, so scientists have been watching it closely.

“It looks like we’ve lost control of melting of the West Antarctic Ice Sheet,” says lead author Dr Kaitlin Naughten, a researcher at the British Antarctic Survey.

“If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago.

“The bright side is that by recognising this situation in advance, the world will have more time to adapt to the sea level rise that’s coming. If you need to abandon or substantially re-engineer a coastal region, having 50 years lead time is going to make all the difference.”

Naughten and colleagues used a model to predict how the oceans would warm in the Amundsen Sea, to the region’s west, a major source of ice loss for the sheet.

They examined changes to ocean heat under different emissions and warming scenarios. This included one scenario consistent with the Paris Agreement target of 1.5°C of warming, and one consistent with moderate action on emissions reductions and about 3°C of warming (this is roughly where current global emissions trends are taking us).

The most ambitious scenario (1.5°C of warming) still had little influence over ocean warming and thus the collapse of the sheet. Even with mitigation, the researchers believe the ocean will warm at three times the current rate.

“The impact of sea level rise on the coast is not just a slow increase of water lapping at the shore – it increases the frequency of coastal flooding events when storms occur,” says Dr Tom Mortlock, a senior analyst at Aon and adjunct fellow at the University of New South Wales Climate Change Research Centre, who was not involved with the research.

“Coastal engineers use the rule of thumb that every 10cm of sea level rise increases the frequency of a given coastal flood by a factor of three.

“Most of our coastal infrastructure has sea level rise allowances built into the design. However, these will typically include median estimates of sea level rise provided by the IPCC, not much more that 1 m by 2100.

“Extreme rates of sea level rise – triggered by tipping points such as the collapse of the West Antarctic Ice Sheet – are extremely difficult to incorporate into coastal risk management. This is because projections remain highly uncertain, and we have little idea of the probability and timing of this occurring.”

Mortlock points out that this research was done “using only a single model and forcing field”, nevertheless it “highlights the urgency with which we need to better understand these high-magnitude sea level rise scenarios in order to incorporate them into risk-based coastal management”.

“The new results in this paper suggest that the huge changes we’ve seen in the Amundsen Sea region are unlikely to be aberrations – they are glimpses into a future that we can no longer avoid,” says Dr Edward Doddridge, a physical oceanographer with the Australian Antarctic Program Partnership at the Institute for Marine and Antarctic Studies, University of Tasmania, who also wasn’t involved with the research.

“It is confronting to think that 5m of sea level rise is already locked in. But we should not see this result as a reason to despair, rather as an urgent call to action. Yes, climate change will negatively impact the future, but through our actions right now we can choose how bad it gets.”

Professor Matt King, also at the University of Tasmania, says he would “not rule out the West Antarctic Ice Sheet being saved by rapid climate action despite this study”.

“Even cutting-edge studies like this can’t yet consider all the processes that may be important to the future of the ice sheet,” says King, who wasn’t involved in the research.

“Hundreds of billions of dollars of Australian infrastructure and tens of thousands of homes are vulnerable to even 1m of sea level rise, and that is at play this century. Many of our regional neighbours are even more exposed.

“[…] If we’re all going to adapt to rising sea levels in a sensible way, we have to be able to say more confidently how much and how fast. That will require new knowledge of how Antarctica works that can be rapidly turned into more confident predictions of the future of sea levels.”