The Paris Climate Agreement and future sea-level rise from Antarctica

The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius 1 . The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer timescales through a combination of ocean thermal expansion and loss of land ice 2 . The Antarctic Ice Sheet (AIS) is Earth’s largest land ice reservoir (equivalent to 57.9 metres of GMSL) 3 , and its ice loss is accelerating 4 . Extensive regions of the AIS are grounded below sea level and susceptible to dynamical instabilities 5,6,7,8 that are capable of producing very rapid retreat 8 . Yet the potential for the implementation of the Paris Agreement temperature targets to slow or stop the onset of these instabilities has not been directly tested with physics-based models. Here we use an observationally calibrated ice sheet–shelf model to show that with global warming limited to 2 degrees Celsius or less, Antarctic ice loss will continue at a pace similar to today’s throughout the twenty-first century. However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100—an order of magnitude faster than today 4 . More fossil-fuel-intensive scenarios 9 result in even greater acceleration. Ice-sheet retreat initiated by the thinning and loss of buttressing ice shelves continues for centuries, regardless of bedrock and sea-level feedback mechanisms 10,11,12 or geoengineered carbon dioxide reduction. These results demonstrate the possibility that rapid and unstoppable sea-level rise from Antarctica will be triggered if Paris Agreement targets are exceeded.

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Data availability

Model-generated data associated with this work are available with this paper. Three-dimensional ice-sheet model output associated with Fig. 2 and Extended Data Figs. 3, 5 are available at the ScholarWorks@UMASS Amherst repository (https://doi.org/10.7275/j005-r778). Climate model forcing used in our main ensembles and meltwater-feedback simulations (Fig. 1) are reported in refs. 46,80 . Source data are provided with this paper.

Code availability

The modified ice-sheet model codes based on ref. 51 are available from the corresponding author. CESM1.2.2 GCM 87 is available from NCAR (https://www.cesm.ucar.edu/models/cesm1.2/) and the RCM is reported in ref. 79 . The Earth–sea level model is described in refs. 12,49 .

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Acknowledgements

We thank T. Naish for guidance on Pliocene sea-level targets. This research was supported by the NSF under awards 1664013, 2035080, 1443347 and 1559040, and by a grant to the NASA Sea Level Change Team 80NSSC17K0698.

Author information

Authors and Affiliations

  1. Department of Geosciences, University of Massachusetts Amherst, Amherst, MA, USA Robert M. DeConto, Shaina Sadai & Dawei Li
  2. Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA, USA David Pollard & Richard B. Alley
  3. Department of Geosciences, Pennsylvania State University, University Park, PA, USA Richard B. Alley
  4. Earth System Science, University of California, Irvine, CA, USA Isabella Velicogna
  5. School of Geographical Sciences, University of Bristol, Bristol, UK Edward Gasson
  6. Department of Earth and Planetary Sciences, McGill University, Montreal, Quebec, Canada Natalya Gomez
  7. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA Alan Condron
  8. Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA Daniel M. Gilford, Erica L. Ashe & Robert E. Kopp
  9. School of Oceanography, Shanghai Jiao Tong University, Shanghai, China Dawei Li
  10. Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA Andrea Dutton
  1. Robert M. DeConto