Understanding the drivers and predictability of record low Antarctic sea ice in austral winter 2023

Since the start of the satellite record in 1978, the three lowest summertime minima in Antarctic sea ice area all occurred within the last seven years and culminated in record low sea ice in austral winter 2023. During this period sea ice area was over 2 million km2 below climatology, a 5 sigma anomaly and 0.9 million km2 below the previous largest seasonal anomaly. Here we show that a fully-coupled Earth System Model nudged to observed winds reproduces the record low, and that the 2023 transition from La Niña to El Niño had minimal impact. Using an ensemble, we demonstrate that  ~ 70% of the anomaly was predictable six months in advance and driven by warm Southern Ocean conditions that developed prior to 2023, with the remaining  ~ 30% attributable to 2023 atmospheric circulation. An ensemble forecast correctly predicted that near record low sea ice would persist in austral winter 2024, due to persistent warm Southern Ocean conditions. 70% of the Antarctic sea ice area’s record low anomaly in 2023 was due to warm Southern Ocean sea surface temperatures, while 30% was due to atmospheric circulation, and the transition from La Niña to El Niño had minimal impact, according to results from a fully-coupled Earth system model nudged to observed atmospheric circulation.