Antarctica’s role in rising seas could be less than feared

The predicted collapse of the Antarctic ice sheet may not have as much of an impact on sea level rise as was initially feared, new studies have suggested.

Two new papers published in the academic journal Nature have called into doubt claims made in 2016 about the collapse of unstable Antarctic ice cliffs into the ocean, caused by rising global temperatures and melting ice shelves.

The high-profile predictions claimed that this type of cliff collapse could add more than a metre to rising seas by 2100.

Instead, the new papers have agreed that these predictions may have been overestimated, with both concluding that the Antarctic ice sheet will likely only contribute around 14-15 cm to sea level rise by 2100, even if greenhouse gas concentrations are very high.

Dr Tamsin Edwards, lecturer in physical geography at King’s College London (KCL), who led the work on one paper, said: ‘Unstable ice-cliffs in Antarctica were proposed as a cause of unstoppable collapse of large parts of the ice sheet in the past.

‘They were, therefore, also predicted to cause rapidly rising seas with global warming in our near future. But we’ve re-analysed the data and found this isn’t the case.’

In one paper researchers from KCL and the University of Bristol looked at ice losses from three specific periods in more detail: three million years ago, 125,000 years ago and over the past 25 years.

They found that ice cliff collapses of the kind suggested three years ago weren’t needed to reproduce previous sea rises, meaning that future projections may have been way out.

The researchers concluded that even if ice-cliff instability is taken into account, there is only a 5% chance that the Antarctic will contribute more than 39cm to global sea rise by 2100 – far lower than the extreme predictions made in 2016.

Professor Tony Payne, a co-author on the paper and professor in Bristol’s School of Geographical Sciences, said: ‘This is a significant step forward in efforts to reconcile recent estimates of future sea level rise and will of great use in the upcoming Intergovernmental Panel on Climate Change assessment of the impacts of future climate change.

‘It is also a useful reminder of the caution required in using geological data to constrain future sea level rise.’

The second paper, led by associate professor Nick Golledge from Victoria University of Wellington, found that current climate projection models do not consider the full effect of ice sheets melting in Greenland and Antarctica.

Image credit: NASA/Christy Hansen