Increasing greenhouse gas emissions are warming our planet at an unprecedented rate and scale. While anthropogenic warming has no direct historical parallel, warm episodes in Earth’s history can offer clues as to the future.
An international research team investigated what happened to the West Antarctic Ice Sheet during the Last Interglacial, over 100,000 years ago. During this period the polar regions were about 3°C warmer than present and sea level was significantly higher.
The results show that while the West Antarctic Ice Sheet shrunk significantly during the Last Interglacial, it didn’t collapse entirely; with the nearby Ronne Ice Shelf remaining at roughly its modern-day extent.
The West Antarctic Ice Sheet holds enough fresh water to raise sea level by around 3-4 metres. This ice sheet is particularly vulnerable to warming because its bowl shape allows seawater to flow under its rim and slowly melt its base. The Ronne Ice Shelf stretches out from the ice sheet into the Atlantic Ocean, forming a floating platform that acts like a buttress to hold back and protect glaciers in-land.
We collected a 651-metre-long ice core from Skytrain Ice Rise, a coastal dome next to the Ronne Ice Shelf. The site is close enough to the West Antarctic Ice Sheet to witness its shrinkage whilst remaining intact.
By dating the ice and analysing the composition of water isotopes in the ice core, the researchers found that the West Antarctic Ice Sheet was partially lost during this time interval, shrinking to perhaps half its modern-day mass. They also measured sea salt contents of the core to gauge the amount of sea spray and therefore the site’s proximity to the coast. This isn’t the catastrophic ice sheet collapse that some model reconstructions have suggested could have happened at this time. Scientists have clear evidence that sea level was several metres above present during last interglacial. The loss of the West Antarctic Ice Sheet had been thought to be the most likely contributor.
These findings will help improve model simulations used to forecast what could happen to ice sheets as our climate warms. The largest uncertainty in long-term sea level projections, including those made by the IPCC, is the fate and stability of the West Antarctic Ice Sheet (WAIS).
Authors: Eric W. Wolff, Robert Mulvaney, Mackenzie M. Grieman, Helene M. Hoffmann, Jack Humby, Christoph Nehrbass-Ahles, Rachael H. Rhodes, Isobel F. Rowell, Louise C. Sime, Hubertus Fischer, Thomas F. Stocker, Amaelle Landais, Frédéric Parrenin, Eric J. Steig, Marina Dütsch & Nicholas R. Golledge
Nature, 2025, https://www.nature.com/articles/s41586-024-08394-w