Abstract. It remains uncertain at which volume threshold the Greenland Ice Sheet (GrIS) mass loss will become irreversible under continuous warming and if the GrIS could regrow under pre-industrial (PI) CO2 concentrations. We use a newly developed comprehensive fully-coupled climate–ice sheet model to explore a potential multistability of the GrIS. This model system is more complex, includes interactive GrIS and Antarctic Ice Sheets (AIS) and more critical feedbacks relevant for the stability of the GrIS than previously used models. Our steady-state simulations indicate at least four steady states under PI CO2 concentrations: a state with a large GrIS, similar to the PI and current state, and three smaller states with GrIS volumes of about 50 %, 30 % and 20 % of the PI volume. These steady states are stable through the interplay of several feedback processes. The most important ones are the melt–elevation and melt–albedo feedback. We also show that interactions between the GrIS and the AIS impact the transient behavior of the GrIS. Our results highlight the importance of fully-coupled climate–ice sheet feedbacks in maintaining multiple steady states of the GrIS. Such multistability has implications for assessing the consequences of global warming. Our simulations indicate that if the GrIS volume drops below a critical threshold of 83 %–70 % of its PI volume, at least half of its current volume will be irreversibly lost even if we return to global PI temperatures through a reduction in CO2 concentrations.
Andernach et al. (Wed,) studied this question.