Quantifying the risk of unprecedented Antarctic heatwaves

It has been widely documented that the East Antarctic heatwave (EAH) in March 2022 featured some of the largest positive temperature anomalies ever recorded anywhere on Earth. The heatwave was extraordinary in both extent and magnitude, where anomalies of at least 30°C were reached widely in the region. This study seeks to determine the likelihood of this event, the risk of even more extreme events occurring in the current state of the Antarctic climate; and whether events of a similar magnitude could occur elsewhere on the continent and at other times of year, with potentially more severe impacts for ice shelf stability. A large ensemble of seasonal hindcasts from multiple forecasting centres is used to assess the simulated occurrence of high temperature extremes over Antarctica, using a technique known as "UNprecedented Simulated Extremes using Ensembles" (UNSEEN).

The March 2022 EAH was outside the range of possible extreme temperatures suggested by the ensemble of hindcasts, signifying that events of this magnitude are incredibly rare. It is also shown with the ensemble that almost everywhere in Antarctica could experience unprecedented March heatwaves in the current climate, at least 5°C higher than has been observed. The UNSEEN method also suggests that temperature anomalies of a similar magnitude to those in the March 2022 EAH could occur widely across the continent in today’s climate. Therefore, Antarctic heatwaves on the scale of the 2022 event could occur almost anywhere, even though they have not yet been observed. This would be particularly problematic over the larger ice shelves of the Ross and Ronne-Filchner. If the extreme temperatures suggested by UNSEEN are realised here, it is shown that these ice shelves would be more susceptible to more frequent, or more severe, melting. This could ultimately result in weaker ice shelves, ice shelf collapse, and rising global sea levels.