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

A. Levermann, R. Winkelmann, S. Nowicki, J. L. Fastook, K. Frieler, R. Greve, H. H. Hellmer, M. A. Martin, M. Mengel, A. J. Payne, D. Pollard, T. Sato, R. Timmermann, W. L. Wang and R. A. Bindschadler


The largest uncertainty in projections of future sea-level change still results from the potentially changing dynamical ice discharge from Antarctica. While ice discharge can alter through a number of processes, basal ice-shelf melting induced by a warming ocean has been identified as a major if not the major cause for possible additional ice flow across the grounding line. Here we derive dynamic ice-sheet response functions for basal ice-shelf melting using experiments carried out within the Sea-level Response to Ice Sheet Evolution (SeaRISE) intercomparison project with five different Antarctic ice-sheet models. As used here these response functions provide separate contributions for four different Antarctic drainage regions. Under the assumptions of linear-response theory we project future ice-discharge for each model, each region and each of the four Representative Concentration Pathways (RCP) using oceanic temperatures from 19 comprehensive climate models of the Coupled Model Intercomparison Project, CMIP-5, and two ocean models from the EU project Ice2Sea. Uncertainty in the climatic forcing, the oceanic response and the ice-model differences is combined into an uncertainty range of future Antarctic ice discharge induced from basal ice-shelf melt. The additional ice loss (Table 6) is clearly scenario-dependent and results in a median of 0.07 m (66%-range: 0.04-0.10 m; 90%-range: -0.01-0.26 m) of global sea-level equivalent for the low-emission RCP-2.6 scenario and yields 0.1 m (66%-range: 0.06-0.14 m; 90%-range: -0.01-0.45 m) for the strongest RCP-8.5. If only models with an explicit representation of ice shelves are taken into account the scenario dependence remains and the values change to: 0.05 m (66%-range: 0.03-0.08 m) for RCP-2.6 and 0.07 m (66%-range: 0.04-0.11 m) for RCP-8.5. These results were obtained using a time delay between the surface warming signal and the subsurface oceanic warming as observed in the CMIP-5 models. Without this time delay the ranges for all ice models changes to 0.10 m (66%-range: 0.07-0.12 m; 90%-range: 0.01-0.28 m) for RCP-2.6 and 0.15 m (66%-range: 0.10-0.21 m; 90%-range: 0.02-0.53 m) for RCP-8.5. All probability distributions as provided in Fig. 10 are highly skewed towards high values.

The Cryosphere Discussions 6 (4), 3447-3489 (2012).

Last modified: 2013-03-21