Assessing the likelihood of unprecedented antarctic heat in the current climate

East Antarctica experienced two recent heat waves with no historical precedent, in March 2022 in Wilkes Land (WL) and in July–August 2024 in Dronning Maud Land (DML). In this study, a large ensemble of seasonal hindcasts is used with the “unprecedented simulated extremes using ensembles” (UNSEEN) technique to contextualize these events by determining whether similar or even more extreme events are possible in the current climate. The observed WL March 2022 event was so extraordinary that the anomaly in UNSEEN’s most extreme event was at least 7.5 K smaller, and it is suggested that small-scale processes contributing to this heat wave are not represented accurately in the ensemble. However, record-breaking geopotential height anomalies are possible, exceeding 100 m above the observed, but only have a 0.1% chance of occurring every year. Furthermore, the UNSEEN ensemble suggests that the magnitude of the winter 2024 event could be exceeded in DML by up to 0.7 K, albeit with a very low likelihood. Similarly, across the Antarctic continent as a whole, UNSEEN analysis suggests that temperature anomaly records could be broken almost anywhere, by several kelvins in the most extreme cases. Additionally, the UNSEEN method is applied to January to ascertain the risk of unprecedented impacts during the peak melting season. If the temperature extremes from UNSEEN are realized, unprecedented melting frequency and intensity over ice shelves in the Antarctic Peninsula in particular could occur under current climatic conditions, impacting ice shelf stability and global sea levels.