The West Antarctic Ice Sheet could reach its tipping point with only minimal additional ocean warming – with long-term consequences for global sea levels. But a small window of time remains to take countermeasures.
The future of the West Antarctic Ice Sheet will be decided within the next few years. This is the alarming conclusion of a new study published at the end of May in the journal Nature Communications Earth & Environment by an international team of researchers, including scientists from Germany’s Potsdam Institute for Climate Impact Research (PIK).
Using computer models, the researchers simulated how the massive West Antarctic Ice Sheet responded to warming phases over the course of the past 800,000 years of glacial cycles. They found that a deep ocean temperature increase of just 0.25 °C – if even that – above current levels could be enough to trigger an irreversible collapse of the ice sheet over the course of millennia. This slight warming of the deep ocean could occur within the next few decades.
According to the study, such a collapse would eventually contribute around four meters to global sea-level rise – a change with drastic consequences for millions of people in coastal regions around the world. While this rise would unfold over centuries rather than just a few decades, the course for it could be set very soon.
Between stability and collapse
“In the past 800,000 years, the Antarctic Ice Sheet has had two stable states that it has repeatedly tipped between,” explains lead author David Chandler of NORCE in a PIK press release. “One, with the West Antarctic Ice Sheet in place, is the state we are currently in. The other state is where the West Antarctic Ice Sheet has collapsed.”
The shift between these two states is driven primarily by the temperature of the surrounding ocean. Atmospheric temperature plays little role, as the edges of the Antarctic Ice Sheet melt mainly due to relatively warm deep water that rises and flows beneath the ice shelves.
Once the tipping point is crossed, ice loss becomes self-sustaining, says Chandler. The collapse of the ice sheet then becomes inevitable and “practically irreversible”. To return it to its current stable state, temperatures would have to remain at or below pre-industrial levels for several thousand years.
The researchers also conclude that the Antarctic Ice Sheet is already in a so-called “overshoot” state – or very close to it. In other words, the conditions that could trigger an irreversible long-term collapse may already be in place, even if the consequences unfold only gradually over the course of centuries.
A question of responsibility
“We have run very long simulations over almost one million year including 8 interglacial periods, when the climate was similar to today,” Dr. Torsten Albrecht, researcher at PIK and co-author of the study, explains to polarjournal.net in an email.
For different climate conditions, the researchers also ran equilibrium simulations over periods of tens of thousands of years and identified two distinct stability regimes. They found that even small changes in ocean temperature can lead to very different long-term states of the Antarctic Ice Sheet. This means that major changes could already be underway – or triggered in the near future – even if they only fully unfold over timescales beyond a human lifetime.
“So this knowledge brings quite some responsibility for today’s society,” emphasizes Albrecht. However, projections of how quickly sea levels could actually rise were not part of the study.
Cutting emissions would still make a difference
Despite the alarming findings, the researchers still see room for action. A rapid reduction in human-made emissions would not only slow global warming but also help stabilize ocean temperatures in the medium term
“The global warming we have seen so far is 100% human made, as the last IPCC report points out. So it is still in our hands,” says Albrecht.
If global average temperatures – including in the Southern Ocean – can be stabilized at a low level, there is still a realistic chance that the ice sheet will remain in its current state.
Dr. Albrecht emphasizes what climate scientists have been warning about for years regarding other tipping points and climate change in general: “With every decade we wait, with every (currently two tenth of a) degree of additional warming, the risk for tipping increases. If we manage to stabilize the global mean temperatures – also in the Southern Ocean – at a low level, we have a chance that the ice sheet remains in the current state.”
“It takes tens of thousands of years for an ice sheet to grow, but just decades to destabilize it by burning fossil fuels. Now we only have a narrow window to act.”
Julius Garbe, PhD student at PIK and co-author of the study
A look into the past as a warning
The strength of the study lies in its exceptionally long time frame: the simulations span eight complete glacial cycles – a period longer than in many previous studies and used for the first time to specifically investigate tipping points in the Antarctic ice sheet system.
The Antarctic Ice Sheet has repeatedly responded to relatively small temperature fluctuations in the past, the authors write. This lends additional weight to their findings, as it shows that the risks are real and systemic – not just hypothetical scenarios.
For science, this means that high-resolution data on deep ocean temperatures around Antarctica are urgently needed to better monitor the stability of the ice sheet. For policymakers, it means one thing: the time to act is now.