Letter

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

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Abstract

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 evidence2,3,4 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 regions5,6,7,8, 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 expensive2,3,10 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.

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Acknowledgements

This work was supported by the ice2sea project funded by the European Commission’s 7th Framework Programme through grant number 226375 (ice2sea contribution number ice2sea119), the UK National Centre for Earth Observation, NERC iGlass project, NERC and UK Met Office Joint Weather and Climate Research Programme, and the French National Research Agency (ANR) under the SUMER (Blanc SIMI 6) 2012 project ANR-12-BS06-0018. Most of the computations were performed using the CIMENT infrastructure (https://ciment.ujf-grenoble.fr), which is supported by the Rhône-Alpes region (grant CPER07 13 CIRA; http://www.ci-ra.org). We thank A. Shepherd and M. McMillan for observational data, H. Hellmer and R. Timmerman for model projection data, D. Vaughan and H. Hellmer for discussions about retreat onset, and J. C. Rougier for discussions about experimental design and calibration.

Author information

Author notes

    • Catherine Ritz
    •  & Tamsin L. Edwards

    These authors contributed equally to this work.

Affiliations

  1. CNRS, LGGE, F-38041 Grenoble, France

    • Catherine Ritz
    • , Gaël Durand
    •  & Vincent Peyaud
  2. Université Grenoble Alpes, LGGE, F-38041 Grenoble, France

    • Catherine Ritz
    • , Gaël Durand
    •  & Vincent Peyaud
  3. Department of Environment, Earth and Ecosystems, Faculty of Science, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK

    • Tamsin L. Edwards
  4. Department of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK

    • Tamsin L. Edwards
    •  & Antony J. Payne
  5. British Antarctic Survey, Natural Environment Research Council, Madingley Road, Cambridge CB3 0ET, UK

    • Richard C. A. Hindmarsh

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Contributions

C.R. and V.P. worked on the development of the GRISLI model and did the numerical modelling. C.R. and G.D., with contributions from T.L.E., performed the physics analysis. T.L.E. designed the experiments with contributions from all authors, wrote the manuscript with contributions from C.R. and G.D., and performed the statistical analysis. T.L.E. and C.R. produced the figures and animation, with contributions from G.D. The sampling and geostatistical analysis were produced by A.J.P., and the theoretical conditions of grounding-line retreat were developed by R.A.H., C.R. and G.D.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Tamsin L. Edwards.

Extended data

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains Supplementary Methods, a Supplementary Discussion, Supplementary Data information and additional references.

Excel files

  1. 1.

    Supplementary Table

    This file contains sea level projections.

Zip files

  1. 1.

    Supplementary Data

    This zipped file contains R script and data: projections. The Code to output annual Antarctic posterior projections as the following options: modes (cm SLE), quantiles (cm SLE) or probabilities of non-exceedance (%) for any quantile/threshold and date range. These results correspond to the columns ‘Prob’ (probabilities of non-exceedance) and ‘SLE’ (modes, quantiles) for rows ‘ALL ANT Post’ in the Excel file, but using this script any quantile/threshold and year may be chosen.

Videos

  1. 1.

    Animation of the Amundsen Sea Embayment

    Summary of the projections in ten-year time steps. The black contour shows the projected median grounding line position. The map shows the mean change in surface elevation, with -100 m contour shown in green. Dashed purple lines show the borders of Pine Island Glacier (PIG) and Thwaites Glacier, which together comprise the Amundsen Sea Embayment.

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