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Abstract

Sea level will continue to rise beyond the 22^nd century due to inertia in the climate system, even if temperatures were immediately stabilised, leading to the proposal of more dramatic measures, such as geoengineering. To provide initial sea level contribution (SLC) estimates from the AIS and address long-term commitment and reversibility questions, a set of idealized geoengineering scenarios were performed with the BISICLES ice sheet model. Climate forcings were extended beyond 2100 to 2200 by either fixing the climate at 2100 (2050) levels at the end (middle) of the century (commitment scenarios), or immediately returning to 2015 levels (e.g. via an instantaneous implementation of geoengineering). Results show that for both high (RCP8.5) and low (RCP2.6) forcing scenarios, reverting back to 2015 climate does not prevent significant loss from the AIS. However, if geoengineering methods are adopted in 2050, SLC is lower than in the commitment scenarios. If geoengineering is implemented in 2100, results are more uncertain but indicate a higher SLC over the 22^nd century compared with doing nothing, for RCP8.5 scenarios. This is because increased surface mass balance in the RCP8.5 commitment scenarios offsets more of the dynamic losses than in the geoengineered scenarios. While late implementation of geoengineering may therefore actually be more harmful to the ice sheet when compared with the original global warming it aims to counteract, SLC trajectories do slow for these scenarios, hinting at eventual recovery, indicating the potential reversibility of AIS mass loss beyond 2200.