Articles | Volume 5, issue 2
Earth Syst. Dynam., 5, 271–293, 2014
Earth Syst. Dynam., 5, 271–293, 2014

Research article 14 Aug 2014

Research article | 14 Aug 2014

Projecting Antarctic ice discharge using response functions from SeaRISE ice-sheet models

A. Levermann1,2, R. Winkelmann1, S. Nowicki3, J. L. Fastook4, K. Frieler1, R. Greve5, H. H. Hellmer6, M. A. Martin1, M. Meinshausen1,7, M. Mengel1, A. J. Payne8, D. Pollard9, T. Sato5, R. Timmermann6, W. L. Wang3, and R. A. Bindschadler3 A. Levermann et al.
  • 1Potsdam Institute for Climate Impact Research, Potsdam, Germany
  • 2Institute of Physics, Potsdam University, Potsdam, Germany
  • 3Code 615, Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt MD 20771 USA
  • 4Computer Science/Quaternary Institute, University of Maine, Orono, ME 04469, USA
  • 5Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
  • 6Alfred Wegener Institute, Bremerhaven, Germany
  • 7School of Earth Sciences, The University of Melbourne, 3010 Melbourne, Australia
  • 8Bristol Glaciology Centre, University of Bristol, University Road, Clifton, Bristol BS8 1SS, UK
  • 9Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA

Abstract. The largest uncertainty in projections of future sea-level change results from the potentially changing dynamical ice discharge from Antarctica. Basal ice-shelf melting induced by a warming ocean has been identified as a major cause for additional ice flow across the grounding line. Here we attempt to estimate the uncertainty range of future ice discharge from Antarctica by combining uncertainty in the climatic forcing, the oceanic response and the ice-sheet model response. The uncertainty in the global mean temperature increase is obtained from historically constrained emulations with the MAGICC-6.0 (Model for the Assessment of Greenhouse gas Induced Climate Change) model. The oceanic forcing is derived from scaling of the subsurface with the atmospheric warming from 19 comprehensive climate models of the Coupled Model Intercomparison Project (CMIP-5) and two ocean models from the EU-project Ice2Sea. The dynamic ice-sheet response is derived from linear response functions for basal ice-shelf melting for four different Antarctic drainage regions using experiments from the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. The resulting uncertainty range for the historic Antarctic contribution to global sea-level rise from 1992 to 2011 agrees with the observed contribution for this period if we use the three ice-sheet models with an explicit representation of ice-shelf dynamics and account for the time-delayed warming of the oceanic subsurface compared to the surface air temperature. The median of the additional ice loss for the 21st century is computed to 0.07 m (66% range: 0.02–0.14 m; 90% range: 0.0–0.23 m) of global sea-level equivalent for the low-emission RCP-2.6 (Representative Concentration Pathway) scenario and 0.09 m (66% range: 0.04–0.21 m; 90% range: 0.01–0.37 m) for the strongest RCP-8.5. Assuming no time delay between the atmospheric warming and the oceanic subsurface, these values increase to 0.09 m (66% range: 0.04–0.17 m; 90% range: 0.02–0.25 m) for RCP-2.6 and 0.15 m (66% range: 0.07–0.28 m; 90% range: 0.04–0.43 m) for RCP-8.5. All probability distributions are highly skewed towards high values. The applied ice-sheet models are coarse resolution with limitations in the representation of grounding-line motion. Within the constraints of the applied methods, the uncertainty induced from different ice-sheet models is smaller than that induced by the external forcing to the ice sheets.

Final-revised paper