Effect of elevation feedbacks and climate mitigation on future Greenland ice sheet melt

Abstract. The Greenland Ice Sheet (GrIS) stores freshwater equal to more than seven meters of potential sea level rise and strongly interacts with the Arctic, North Atlantic and global climate. Over the last decades, the GrIS has been losing mass and is projected to lose mass at an increasing rate. Interactions between the GrIS and the climate have the potential to amplify or reduce GrIS mass balance responses to ongoing and projected warming. Here, we investigate the impact of ice sheet-climate interactions on the climate and mass balance of the GrIS using the Community Ice Sheet Model version 2 coupled to the Community Earth System Model version 2 (CESM2-CISM2). To this end, we compare two idealized simulations with a nonevolving and evolving ice sheet topography in which we apply an annual 1 % increase in CO2 concentrations until stabilization at four times pre-industrial (PI) CO2 concentrations (4xCO2). By comparing the 1- and 2-way coupled simulations, we find significant changes in atmospheric blocking, precipitation and cloud formation over Greenland as the GrIS topography evolves, acting as negative feedbacks on mass loss. We also find that a uniform temperature lapse rate represents temperature changes in the ablation area, leading to an overestimation of the positive melt-elevation feedback in the 1-way coupled simulation, resulting in an overestimation of mass loss. Furthermore, we analyze an idealized simulation in which we first apply a 4xPI CO2 forcing and thereafter annually reduce atmospheric CO2 by 5 % until PI concentrations are reached. During the 350 year 4xCO2 forcing period, the ice sheet loses a total mass of 1.1 m sea level equivalent, and part of its margins retreat landward. When the PI CO2 concentration is restored, melt decreases rapidly, leading to a small positive surface mass balance. Combined with the strongly reduced ice discharge resulting from the widespread retreat of the ice sheet margin, this results in the halting of GrIS mass loss, despite a remaining global warming of 2 K. The GrIS, Arctic and North Atlantic ocean strongly interact, causing a complex transitional phase towards a colder climate during the century following the CO2 reduction. Elevated atmospheric temperatures, larger ocean heat transport and a deteriorated state of the snowpack, compared to the initial pre-industrial state, result in limited regrowth of the ice sheet under reintroduced PI CO2 conditions.