Rapid decline in Antarctic sea ice in recent years hints at future change

Following years of record highs, an unexpected and precipitous reduction in Antarctic sea-ice extent started in 2016. This decline, lasting three years, was the most pronounced of the satellite era, equivalent to 30 years of sea-ice loss in the Arctic. Here, we synthesize recent work showing this sea-ice reduction probably resulted from the interaction of a decades-long ocean warming trend and an early spring southward advection of atmospheric heat, with an exceptional weakening of the Southern Hemisphere mid-latitude westerlies in late spring. We discuss what this event reveals about the underlying atmospheric and oceanic dynamical processes that control sea ice in the region and the ways in which shifting climate variability and remote forcings, especially from the tropics, influence these processes. Knowledge gaps show that further work is needed to improve future projections of changes in one of the largest seasonal phenomena on the planet.