A regime shift in seasonal total Antarctic sea ice extent in the twentieth century

In stark contrast to the Arctic, there have been statistically significant positive trends in total Antarctic sea ice extent since 1979. However, the short and highly variable nature of observed Antarctic sea ice extent limits the ability to fully understand the historical context of these recent changes. To meet this challenge, we have created robust, observation-based reconstruction ensembles of seasonal Antarctic sea ice extent since 1905. Using these reconstructions, here we show that the observed period since 1979 is the only time all four seasons demonstrate significant increases in total Antarctic sea ice in the context of the twentieth century and that the observed increases are juxtaposed against statistically significant decreases throughout much of the early and middle twentieth century. These reconstructions provide reliable estimates of seasonally resolved total Antarctic sea ice extent and are skilful enough to better understand aspects of air-sea-ice interactions within the Antarctic climate system. Antarctic sea ice extent is thought to be stable or increasing, in contrast to Arctic declines. Estimates of seasonal Antarctic sea ice from reconstructions show that increases are confined to the satellite era, post-1979, with substantial decreases in the early and mid-twentieth century.

Automated summary

In contrast to the Arctic, there has been a significant increase in Antarctic sea ice extent since 1979. However, the short and highly variable nature of observed Antarctic sea ice extent limits our understanding of its historical context. Through reconstructions, it has been found that the period since 1979 is the only time when all four seasons show a significant increase in Antarctic sea ice, with significant decreases in the early and middle twentieth century. These reconstructions provide reliable estimates of seasonally resolved Antarctic sea ice extent and can improve our understanding of air-sea-ice interactions in the Antarctic climate system.