| Summary: | The Ice Sheet Model Intercomparison for CMIP6 (ISMIP6) is the primary effort of CMIP6 (Climate Model Intercomparison Project Phase 6) focusing on ice sheets. It was designed to provide process-based projections of ice sheets contribution to sea level rise over the 21 st century, and assess uncertainties associated with these projections as well as their origins. However, improved ice sheet projections beyond the 21 st century are also necessary, as instability mechanisms have the potential to rapidly destabilize ice sheets and several regions may reach tipping points, potentially leading to much larger sea level contributions. Continuing on the success of ISMIP6, a new effort targeting Antarctic ice sheet projections until 2300 has been launched in 2022. ISMIP6 Antarctica 2300 Projections extend previous simulations to 2300, based on CMIP5 and CMIP6 climate forcings. We present here the first results assessing the stability of basins around Antarctica beyond 2100 from an ensemble of ice sheet models. Results from this ensemble suggest that while the sea level rise contribution from the Antarctic Ice Sheet remains limited to no more than 30 cm by 2100, it can reach up to 4 meters by 2300. Large retreats are observed in many basins in West Antarctica, especially in the Amundsen Sea Sector as well as on the ice streams feeding the Ross and Ronne-Filchner ice shelves. Changes remain more limited in East Antarctica, but the increased snow precipitation no longer compensates dynamic thinning in this region around 2150. ISMIP6 is supported by the Climate and Cryosphere (CliC) initiative.
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