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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 May 2019

Submitted as: research article | 23 May 2019

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Earth System Dynamics (ESD).

Projecting Antarctica's contribution to future sea level rise from basal ice-shelf melt using linear response functions of 16 ice sheet models (LARMIP-2)

Anders Levermann1,2,3, Ricarda Winkelmann1,3, Torsten Albrecht1, Heiko Goelzer4,5, Nicholas R. Golledge6,7, Ralf Greve8, Philippe Huybrechts9, Jim Jordan10, Gunter Leguy11, Daniel Martin12, Mathieu Morlighem13, Frank Pattyn5, David Pollard14, Aurelien Quiquet15, Christian Rodehacke16, Helene Seroussi17, Johannes Sutter18,19, Tong Zhang20, Jonas Van Breedam9, Robert DeConto21, Christophe Dumas15, Julius Garbe1,3, G. Hilmar Gudmundsson10, Matthew J. Hoffman20, Angelika Humbert18,22, Thomas Kleiner18, William Lipscomb11, Malte Meinshausen23,1, Esmond Ng12, Mauro Perego24, Stephen F. Price20, Fuyuki Saito25, Nicole-Jeanne Schlegel17, Sainan Sun5, and Roderik S. W. van de Wal4,26 Anders Levermann et al.
  • 1Potsdam Institute for Climate Impact Research, Potsdam, Potsdam, Germany
  • 2LDEO, Columbia University, New York, USA
  • 3Institute of Physics and Astronomy, University of Potsdam, Potsdam, 14476, Germany
  • 4Institute for Marine and Atmospheric research Utrecht, Utrecht University, the Netherlands
  • 5Laboratoire de Glaciologie, Université libre de Bruxelles (ULB), Brussels, Belgium
  • 6Antarctic Research Centre, Victoria University of Wellington, Wellington 6140, New Zealand
  • 7GNS Science, Avalon, Lower Hutt 5011, New Zealand
  • 8Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
  • 9Department of Geography, Vrije Universiteit Brussel, Brussels, Belgium
  • 10Department of Geography and Environmental Sciences, University of Northumbria, Newcastle, UK
  • 11Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 12Lawrence Berkeley National Laboratory, Berkeley, CA, USA
  • 13Department of Earth System Science, University of California Irvine, Irvine CA, USA
  • 14Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania, USA
  • 15Laboratoire des Sciences du Climat et de l’Environnement, CEA/CNRS-INSU/UVSQ, Gif-sur-Yvette Cedex, France
  • 16Danish Meteorological Institute, Arctic and Climate, Copenhagen, Denmark
  • 17Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 18Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 19Physics Institute, University of Bern, Bern, Switzerland
  • 20Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
  • 21Department of Geosciences, University of Massachusetts, Amherst, Massachusetts, USA
  • 22Department of Geosciences, University of Bremen, Germany
  • 23Climate & Energy College, School of Earth Sciences, University of Melbourne, Parkville, Victoria, Australia
  • 24Center for Computing Research, Sandia National Laboratories, Albuquerque, New Mexico, 87185, USA
  • 25Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • 26Geosciences, Physical Geography, Utrecht University, Utrecht, the Netherlands

Abstract. The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty that arises from large uncertainty in the external forcing that future warming may exert onto the ice sheet. While ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean, the approach is neglecting a number of processes such as surface mass balance related contributions and mechanisms. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any dampening or self-amplifying processes. This is particularly relevant in situations where an instability is dominating the ice loss. Results obtained here are thus relevant in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014), but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP-5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP-5 models in relation to the global mean surface warming) and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 is 9.6 mm with a likely range between 5.2 mm and 20.3 mm compared to the observed sea-level contribution from Antarctica of 7.4 mm with a standard deviation of 3.7 mm (Shepherd et al., 2018). For the so-called business-as-usual warming path, RCP-8.5, we obtain a median contribution of the Antarctic ice sheet to global mean sea-level rise within the 21st century of 17 cm with a likely range (66-percentile around the mean) between 9 cm and 36 cm and a very likely range (90-percentile around the mean) between 6 cm and 59 cm. For the RCP-2.6 warming path which will keep the global mean temperature below two degrees of global warming and is thus consistent with the Paris Climate Agreement yields a median of 13 cm of global mean sea-level contribution. The likely range for the RCP-2.6 scenario is between 7 cm and 25 cm and the very likely range is between 5 cm and 39 cm. The structural uncertainties in the method do not allow an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario, separately. The rate of sea level contribution is highest under the RCP-8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade with a likely range between 2 cm/dec and 8 cm/dec and a very likely range between 1 cm/dec and 13 cm/dec.

Anders Levermann et al.
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Short summary
We provide an estimated of the future sea level contribution of Antarctica from basal ice shelf melting up to the year 2100. The full uncertainty range in warming related forcing of basal melt is estimated and applied to 16 state-of-the-art ice sheet models using a linear response theory approach. The sea level contribution we obtain is very likely below 59 cm under unmitigated climate change until 2100 (RCP-8.5) and very likely below 39 cm if the Paris Climate Agreement is kept.
We provide an estimated of the future sea level contribution of Antarctica from basal ice shelf...