Abstract
Abstract. Projection of the contribution of ice sheets to sea level change as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form of simulations from coupled ice sheet–climate models and stand-alone ice sheet models, overseen by the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). This paper describes the experimental setup for process-based sea level change projections to be performed with stand-alone Greenland and Antarctic ice sheet models in the context of ISMIP6. The ISMIP6 protocol relies on a suite of polar atmospheric and oceanic CMIP-based forcing for ice sheet models, in order to explore the uncertainty in projected sea level change due to future emissions scenarios, CMIP models, ice sheet models, and parameterizations for ice–ocean interactions. We describe here the approach taken for defining the suite of ISMIP6 stand-alone ice sheet simulations, document the experimental framework and implementation, and present an overview of the ISMIP6 forcing to be used by participating ice sheet modeling groups.
Highlights
The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is a targeted activity of the Climate and Cryosphere (CliC) project of the World Climate Research Project (WCRP) and has been formally endorsed by the Coupled Model Intercomparison Project Phase 6 (CMIP6; Eyring et al, 2016)
This paper describes the detailed experimental protocol used for stand-alone experiments with ice sheet models of Greenland and Antarctica using forcing from CMIP atmosphere–ocean general circulation model (AOGCM), and it presents the novel atmospheric and oceanic forcing datasets prepared by ISMIP6
For the Greenland ice sheet, ISMIP6 generated surface forcing from CMIP AOGCMs that have been reinterpreted through the Modèle Atmosphérique Régionale (MAR) regional climate model
Summary
The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is a targeted activity of the Climate and Cryosphere (CliC) project of the World Climate Research Project (WCRP) and has been formally endorsed by the Coupled Model Intercomparison Project Phase 6 (CMIP6; Eyring et al, 2016). Nowicki et al (2016) describe the overall design of ISMIP6, which includes an assessment of the impact of initial conditions on projections (ISMIP6-initMIP; Goelzer et al, 2018; Seroussi et al, 2019), experiments in which ice sheet models are fully coupled within Earth system models (ISM–ESMs), and experiments with stand-alone ice sheet models (ISM) forced by output from the CMIP AOGCM. Specific challenges included (i) the translation of the various AOGCM resolutions and grids to the various ISM grid resolutions; (ii) the poor representation of steep gradients in the surface topography of the ice sheet margins within AOGCMs, which underestimates large gradients in atmospheric forcing; (iii) the quality of AOGCM polar climate; and (iv) the mismatch in the spatial extents of ice sheets within the AOGCMs and initialized ice sheet extent within certain ISMs. oceanic variables from AOGCMs needed to be extrapolated from continental shelves to provide boundary conditions underneath ice shelves and at the calving front, as AOGCMs typically do not resolve ice shelf cavities and proglacial fjords.
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