ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century
Authors: Seroussi Hélène , Nowicki Sophie , Payne Antony J. , Goelzer Heiko , Lipscomb William H. , Abe-Ouchi Ayako , Agosta Cécile , Albrecht Torsten , Asay-Davis Xylar , Barthel Alice , Calov Reinhard , Cullather Richard , Dumas Christophe , Galton-Fenzi Benjamin K. , Gladstone Rupert , Golledge Nicholas R. , Gregory Jonathan M. , Greve Ralf , Hattermann Tore , Hoffman Matthew J. , Humbert Angelika , Huybrechts Philippe , Jourdain Nicolas C. , Kleiner Thomas , Larour Eric , Leguy Gunter R. , Lowry Daniel P. , Little Chistopher M. , Morlighem Mathieu , Pattyn Frank , Pelle Tyler , Price Stephen F. , Quiquet Aurélien , Reese Ronja , Schlegel Nicole-Jeanne , Shepherd Andrew , Simon Erika , Smith Robin S. , Straneo Fiammetta , Sun Sainan , Trusel Luke D. , Van Breedam Jonas , van de Wal Roderik S. W. , Winkelmann Ricarda , Zhao Chen , Zhang Tong , Zwinger Thomas 
Published: September 2020

Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in
response to different climate scenarios and assess the mass loss that would contribute to
future sea level rise. However, there is currently no consensus on estimates of the future mass
balance of the ice sheet, primarily because of differences in the representation of physical
processes, forcings employed and initial states of ice sheet models. This study presents
results from ice flow model simulations from 13 international groups focusing on the evolution
of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model
Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the
Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate
model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response
to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent
(SLE) under Representative Concentration
Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with
constant climate conditions and should therefore be added to the mass loss contribution under
climate conditions similar to present-day conditions over the same period. The simulated evolution of the
West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and
8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing
the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf
collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of
ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice
shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the
calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities
and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based
on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to
simulations done under present-day conditions for the two CMIP5 forcings used and display
limited mass gain in East Antarctica.