Sea-level rise from Antarctic collapse may be slower than suggested.

A new study by scientists in the UK and France has found that Antarctic ice sheet collapse will have serious consequences for sea level rise over the next two hundred years, though not as much as some have suggested.This study, published this week in the journal Nature, uses an ice-sheet model to predict the consequences of unstable retreat of the ice, which recent studies suggest has begun in West Antarctica.

An international team of researchers, including a scientist from British Antarctic Survey (BAS), predict that the contribution is most likely to be 10 cm of sea-level rise this century under a mid to high climate scenario, but is extremely unlikely to be higher than 30 cm. When combined with other contributions, that’s a significant challenge for adapting to future sea level rise. But it’s also far lower than some previous estimates, which were as high as one metre from Antarctica alone.

The study’s central estimate raises the Intergovernmental Panel on Climate Change (IPCC) central prediction of 60 cm global sea-level rise by just a few centimetres under the mid to high scenario they used. But the team’s method allowed them to assess the likelihood of sea-level rise from substantial parts of the ice sheet collapsing, which the IPCC could not due to a lack of evidence. They predict there is a one in twenty chance that Antarctic collapse could contribute more than 30 cm sea-level rise by the end of the century and more than 72 cm by 2200. This does not rule out larger contributions on longer time scales.

Dr Tamsin Edwards, Lecturer in Environmental Sciences at the OU, says: “Our method is more comprehensive than previous estimates, because it has more exploration of uncertainty than previous model predictions and more physics than those based on extrapolation or expert judgment.”

Dr Dominic Hodgson, a glaciologist at British Antarctic Survey, says: “This study is significant. Advances in modelling are needed to reduce the error in global sea level predictions so that mitigation strategies (and Government expenditure) are focussed on the most likely sea level scenarios. This study takes us one step closer to understanding Antarctica’s likely contribution to future sea level rise.”

The paper ‘Potential sea-level rise from Antarctic ice sheet instability constrained by observations’ is authored by Catherine Ritz (Centre national de la recherche scientifique and Université Grenoble Alpes, France), Tamsin L. Edwards (The Open University, University of Bristol), Gaël Durand (Centre national de la recherche scientifique and Université Grenoble Alpes, France), Antony J. Payne (The University of Bristol), Vincent Peyaud (Centre national de la recherche scientifique and Université Grenoble Alpes, France) and Richard C.A. Hindmarsh (British Antarctic Survey). It was published on Wednesday 18 November 2015 in the academic journal Nature:

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations

Catherine Ritz, Tamsin L. Edwards, Gaël Durand, Antony J. Payne, Vincent Peyaud

 

Nature (2015) doi:10.1038/nature16147 - Published online 18 November 2015 

Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI)¹, a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence^{2, 3, 4} that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions^{5, 6, 7, 8}, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging⁹: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive^{2, 3, 10} to generate large ensembles for uncertainty assessment, and lower-resolution model projections¹¹ rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments⁹ (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.