Description and Demonstration of the Coupled Community Earth System Model v2 - Community Ice Sheet Model v2 (CESM2-CISM2).

Laura Muntjewerf,Jan T M Lenaerts,Miren Vizcaino,Raymond Sellevold,Marcus Lofverstrom,Carolina Ernani Da Silva,Jeremy Fyke,William H Lipscomb,William J Sacks,Katherine Thayer-Calder

doi:10.1029/2020ms002356

Abstract

Earth system/ice‐sheet coupling is an area of recent, major Earth System Model (ESM) development. This work occurs at the intersection of glaciology and climate science and is motivated by a need for robust projections of sea‐level rise. The Community Ice Sheet Model version 2 (CISM2) is the newest component model of the Community Earth System Model version 2 (CESM2). This study describes the coupling and novel capabilities of the model, including: (1) an advanced energy‐balance‐based surface mass balance calculation in the land component with downscaling via elevation classes; (2) a closed freshwater budget from ice sheet to the ocean from surface runoff, basal melting, and ice discharge; (3) dynamic land surface types; and (4) dynamic atmospheric topography. The Earth system/ice‐sheet coupling is demonstrated in a simulation with an evolving Greenland Ice Sheet (GrIS) under an idealized high CO2 scenario. The model simulates a large expansion of ablation areas (where surface ablation exceeds snow accumulation) and a large increase in surface runoff. This results in an elevated freshwater flux to the ocean, as well as thinning of the ice sheet and area retreat. These GrIS changes result in reduced Greenland surface albedo, changes in the sign and magnitude of sensible and latent heat fluxes, and modified surface roughness and overall ice sheet topography. Representation of these couplings between climate and ice sheets is key for the simulation of ice and climate interactions.

Highlights

Land ice exists in the Earth system where perennial snow fields can form and develop into flowing ice masses (Agassiz, 1840)
This study presents the coupling and utility of the Community Earth System Model version 2 (CESM2) with the Community Ice Sheet Model version 2 (CISM2)
The analysis focuses on behavior of the four coupling aspects that are described in Section 3 (SMB, ocean freshwater budget from Greenland, dynamic ice sheet margins, and surface topography updating)

Summary

Introduction

Land ice exists in the Earth system where perennial snow fields can form and develop into flowing ice masses (Agassiz, 1840). Once land ice has formed, the climate modulates ice dynamics by controlling processes of mass loss and gain at the ice sheet boundaries (Nye, 1963). As ice sheets evolve, they interact with the climate in ways that modify their own evolution (Fyke et al, 2018). The Earth system contains many such feedback mechanisms, including both positive (amplifying) and negative (moderating) processes. Feedback mechanisms between ice sheets and climate have been extensively studied.

Results

Discussion

Conclusion