Abstract
Ice sheet processes are often simplified in global climate models as changes in ice sheets have been assumed to occur over long time scales compared to ocean and atmospheric changes. However, numerous observations show an increasing rate of mass loss from the Greenland Ice Sheet and call for comprehensive process-based models to explore its role in climate change. Here, we present a new model system, EC-Earth-PISM, that includes an interactive Greenland Ice Sheet. The model is based on the EC-Earth v2.3 global climate model in which ice sheet surface processes are introduced. This model interacts with the Parallel Ice Sheet Model (PISM) without anomaly or flux corrections. Under pre-industrial climate conditions, the modeled climate and ice sheet are stable while keeping a realistic interannual variability. In model simulations forced into a warmer climate of four times the pre-industrial CO2 concentration, the total surface mass balance decreases and the ice sheet loses mass at a rate of about 500 Gt/year. In the climate warming experiments, the resulting freshwater flux from the Greenland Ice Sheet increases 55% more in the experiments with the interactive ice sheet and the climate response is significantly different: the Arctic near-surface air temperature is lower, substantially more winter sea ice covers the northern hemisphere, and the ocean circulation is weaker. Our results indicate that the melt-albedo feedback plays a key role for the response of the ice sheet and its influence on the changing climate in the Arctic. This emphasizes the importance of including interactive ice sheets in climate change projections.
Highlights
Global climate models often assume a stable, non-responding, Greenland Ice Sheet (GrIS) or a very simple treatment of ice sheet processes because the ice sheet time-scales are assumed to be much longer than the time-scales of the atmosphere and the ocean
For the comparison between ECEarth and EC-Earth-Parallel Ice Sheet Model (PISM), the average of the last 50 years of each experiment is considered, i.e. after a stable climate state has been achieved in the two climate warming experiments
All surface fluxes are calculated on the EC-Earth land surface grid and integrated over the GrIS using the EC-Earth-PISM fractional ice mask
Summary
Global climate models often assume a stable, non-responding, Greenland Ice Sheet (GrIS) or a very simple treatment of ice sheet processes because the ice sheet time-scales (millennial and beyond) are assumed to be much longer than the time-scales of the atmosphere and the ocean (seasonal, annual, decadal). The interaction between the ice sheet and the ocean is important as the increased amounts of freshwater from the melting ice sheet may strengthen the vertical upper ocean stratification, which weakens the Atlantic Meridional Overturning Circulation (AMOC; Swingedouw et al 2012, 2014; Bakker et al 2016; Caesar et al 2021). This weakened circulation reduces the oceanic heat supply to the Northern North Atlantic region, and eventually dampens Arctic warming (e.g., Gierz et al 2015; Rahmstorf et al 2015; Hátún et al 2005).
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