The Ice Sheet Model Intercomparison for CMIP6 (ISMIP6) brings together for the first time a consortium of international ice sheet models and coupled ice sheet-climate models to fully explore the sea level rise contribution from the Greenland and Antarctic ice sheets. ISMIP6 is a collaboration between ice sheet and climate modelers, along with observationalists and remote sensed expert over the polar regions.
ISMIP6 was established in fall 2014, but is based on a long history of Ice Sheet Model Intercomparison Projects or ISMIP, including the more recent European ice2sea and COMBINE efforts, and the Sea level Response to Ice Sheet Evolution (SeaRISE) community effort.
The sea level projections made by the glaciological community as part of the Intergovernmental Panel on Climate Change (IPCC) process have often been out of phase with the projections considered by the wider Coupled Model Intercomparison Project (CMIP) community. For instance in AR5, the ice2sea and SeaRISE (Sea-level Response to Ice Sheet Evolution) ice sheet projects predominantly worked with AR4 scenarios, while the CMIP5 community used new RCP scenarios. A primary focus of ISMIP6 is therefore to develop to allow ice sheet models to be better integrated in the CMIP6 initiative, in order to improve both sea level projections due to changes in the cryosphere and our understanding of the cryosphere in a changing climate. These goals map into both the Melting Ice & Global Consequences and Regional Sea-Level Change & Coastal Impacts Grand Challenges relevant to Climate and Cryosphere (CliC) and the World Climate Research Program (WCRP).
The primary goal of ISMIP6 is to improve projections of sea level rise via simulations of the evolution of the Greenland and Antarctic ice sheets under a changing climate, along with a quantification of associated uncertainties (associated with both uncertainty in climate forcing and in the response of the ice sheets). As depicted in Figure 1, this goal requires an evaluation of AOGCM climate over and surrounding the ice sheets; analysis of simulated ice-sheet response from standalone models forced “offline” with CMIP AOGCM outputs and, where possible, with coupled ice sheet-AOGCM models; and experiments with standalone ice sheet models targeted at exploring the uncertainty associated with ice sheets physics, dynamics and numerical implementation. A secondary goal is to investigate the role of feedbacks between ice sheets and climate in order to gain insight into the impact of increased mass loss from the ice sheets on regional and global sea level, and of the implied ocean freshening on the coupled ocean-atmosphere circulation.
ISMIP6 is directly related to the WCRP Grand Challenges on ‘Melting Ice & Global Consequences’ and ‘egional Sea-Level Change & Coastal Impacts’ that the CMIP6 community seek to address. ISMIP6 is primarily focused on the CMIP6 scientific question “How does the Earth System respond to forcing?” and offers the exciting opportunity of widening the current CMIP definition of Earth System to include (for the first time) the ice sheets. The emphasis on standalone, ensemble modeling will also shed light on the question “How can we assess future climate changes given climate variability, predictability and uncertainties in scenario” for the mass budget of the ice sheets and its impact of global sea level.