Future Greenland melt in coupled ice sheet-climate CESM simulations: feedbacks, thresholds, reversibility

Estimates of future Greenland ice sheet (GrIS) melt are mostly based on regional climate modelling for a fixed GrIS topography or on ice sheet modelling with forcing from climate models. This prevents the modelling of climate and GrIS feedbacks and other types of interaction. Here we examine a set of multi-century simulations with the Community Earth System Model featuring an interactive GrIS to explore future relationship between global climate change and ice sheet change. To this end, we compare a set of coupled CESM-CISM 1% CO₂ increase simulations until stabilization at two, two and a half, three and four times pre-industrial CO₂ levels to examine the sensitivity of the GrIS to emission mitigation. Here we find a large role of ocean circulation weakening and associated regional climate changes on GrIS melt for moderate emission scenarios and large melt differences between the three times and four times CO₂ stabilization scenarios. In addition, we examine the role of feedbacks on ice sheet evolution by comparing a 1% to 4xCO₂ coupled simulation with a simulation where the GrIS topography and meltwater fluxes to the ocean are prescribed as pre-industrial. Finally, we explore the effects on GrIS melt rates of a fast 5% CO₂ reduction from four times to pre-industrial levels, with a focus on restoration of high latitude climate, GrIS albedo, surface energy fluxes and refreezing capacity.