The first paper suggests that sustained collapse of Antarctic ice-cliffs into the ocean, caused by rising global temperatures and melting ice shelves, may not have a large impact on sea level rise. This means that high-profile and controversial predictions from 2016, which claimed that this type of cliff collapse could add more than a metre to rising seas by 2100, may be substantially over-estimated.
Dr Tamsin Edwards, Lecturer in Physical Geography at King’s College London, who led the work, explains: “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.”
By looking at ice losses three-million-years ago, 125,000 years ago, and over the last 25 years in more detail, the team show that unstable ice-cliff collapses aren’t needed to reproduce sea level rises in the past. When they remove this proposed mechanism from the model, they predict that there is only a five percent chance that the Antarctic contribution to sea level rise will exceed 39 cm by 2100 - much lower than the previous predictions of over a metre.
Dr Edwards added: “We’ve shown that ice-cliff instability doesn’t appear to be an essential mechanism in reproducing past sea level changes and so this suggests ‘the jury’s still out’ when it comes to including it in future predictions. Even if we do include ice-cliff instability, our more thorough assessment shows that the most likely contribution to sea level rise would be less than half a metre by 2100.”
Professor Tony Payne, a co-author on the paper and professor in Bristol’s School of Geographical Sciences, commented: “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.”
In a second paper, led by Associate Professor Nick Golledge from Victoria University of Wellington, they show that current climate models do not consider the full effect of melting ice sheets in Greenland and Antarctica. Overall, both papers agree that the most likely Antarctic contribution to sea level rise will be around 14 – 15 centimetres under conditions of very high greenhouse gas concentrations.