Abstract
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.
Highlights
A regime shift in seasonal total Antarctic sea ice extent in the twentieth century Ryan L
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
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
Summary
Analysis of these contributions is part of future work, but hopefully the reconstructions presented here will promote an increase in research from many disciplines aimed at further interpreting and unlocking historical variations in Antarctic sea ice extent during the twentieth century. As these reconstructions are highly skilful, they are appropriate to use in further research on evaluating climate models and interpreting the causes of the regime shifts depicted in these reconstructions.
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