Abstract

Ocean models consistently project that with sufficient climate change forcing, the Ross and Filchner-Ronne ice shelf cavities could abruptly transition from a cold state to a warm state. Crossing these tipping points would have profound consequences for basal melt rates, buttressing of ice streams, and ultimately sea level rise. Here we analyse over 14,000 years of “overshoot” simulations with the UK Earth System Model, which includes a fully coupled Antarctic Ice Sheet. As the climate warms, stabilises at different temperatures, and cools again, we simulate many examples of the cavities tipping and recovering. We find that global warming thresholds of around 3.5°C and 5°C tip the Ross and Filchner-Ronne respectively. We also find evidence of hysteresis: the climate must cool back down beyond the tipping thresholds in order for each cavity to return to its original cold state. Even if the oceanography recovers, the ice sheet does not: sea level contribution from each catchment takes centuries even to stabilise, and the ice does not begin to regrow on this timescale. Therefore, if the Ross or Filchner-Ronne Ice Shelves cross tipping points, the resulting sea level rise will be effectively irreversible.