Has the West Antarctic Ice Sheet reached its tipping point? | Polarjournal
Thwaites Glacier is part of the West Antarctic Ice Sheet. Its ice shelf is one of the fastest melting. Like those of the other glaciers in West Antarctica, it extends into the Amundsen Sea. (Photo: David Vaughan)

The West Antarctic Ice Sheet will melt faster and faster and raise sea levels by the end of this century, no matter how much emissions are reduced, according to a new study. Nevertheless, this is no reason to abandon measures to mitigate climate change – on the contrary.

Scientists from the British Antarctic Survey and Northumbria University published their latest research findings on the West Antarctic Ice Sheet (WAIS) earlier this week, and these are more than sobering. Writing in the journal Nature Climate Change, they describe how a significant acceleration in ice melt is “unavoidable” by 2100, regardless of how much and how fast greenhouse gas emissions are reduced.

The research team conducted computer simulations to investigate the melting of the WAIS, the mass loss of which is almost entirely due to the melting of the ice shelves from below due to warming seawater. The results show that the Amundsen Sea, on which the WAIS ice shelves rest, will warm “significantly and over a large area” over the next few decades under all the emission scenarios applied – Paris 1.5°C, Paris 2°C, RCP 4.5 and RCP 8.5.

Even if the most ambitious goal of the Paris Agreement – limiting global warming to 1.5°C – could be met, which is very unlikely from today’s perspective, the Amundsen Sea would warm three times faster than in the 20th century, the study says. The simulations also showed no significant difference between the different scenarios. Only after 2045 would temperatures in the Amundsen Sea rise significantly more under the least favorable scenario with very high emissions than under the more optimistic ones, by up to 2°C by the end of the century. The researchers also took climate fluctuations such as El Niño into account in their calculations.

The team used an ocean model to simulate a historical scenario and four future scenarios in which the development of the temperature of the Amundsen Sea at depths of 200 to 700 metres does not differ significantly until the year 2045. Only after that the forecasts diverge. Graphic: Naughten et al. 2023

The ice shelves of the glaciers making up the WAIS, such as those of Thwaites and Pine Island, are therefore predicted to melt even faster in any case, making a retreat irreversibly and causing the global mean sea level to rise by 5.3 metres over the coming centuries. It is already being observed that the buttressing provided by ice shelves for the glaciers above is decreasing and that these are flowing faster towards the ocean.

Worldwide, more than two billion people live along or near the coast. It was therefore important to the research team to explore a wide range of scenarios to allow policy makers to plan ahead and better adapt to upcoming changes, especially in coastal regions.

The time period examined in the study, beyond 2100, is difficult to grasp, but the authors emphasize that continued ocean warming will trigger further sea-level rise impacts on time scales that are “immediately policy relevant.” In addition, it is not certain to what extent atmospheric warming will play a role in the WAIS in the future.

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

The study does not address whether the West Antarctic Ice Sheet has already passed its tipping point. In an interview with Deutschlandfunk Kultur, Olaf Eisen, professor for glaciology at the Alfred Wegener Institute, who was not involved in this study, stated that at the moment it is not known whether the tipping point has already been reached or whether it will only be in ten or 50 years. However, there is hope that it has not yet been reached.

Even though the results of the study are sobering, now is not the time to bury our heads in the sand. It remains essential to continue to push forward with mitigation in limiting the impacts of climate change, the team of authors said.

“We must not stop working to reduce our dependence on fossil fuels. What we do now will help to slow the rate of sea level rise in the long term. The slower the sea level changes, the easier it will be for governments and society to adapt to, even if it can’t be stopped,” Dr. Naughten said.

The WAIS is only one of the components affecting sea level, and adaptation to sea level rise should now be prioritized. The team concludes its study with, “Limiting the societal and economic costs of sea-level rise will require a combination of mitigation, adaptation and luck.”

Julia Hager, PolarJournal

Contributed image: David Vaughan

Source Naughten, K.A., Holland, P.R. & De Rydt, J. Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century. Nat. Clim. Chang. (2023). https://doi.org/10.1038/s41558-023-01818-x

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