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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.

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Fig. 1: Antarctic seasonal total sea ice extent, 1905–2020.
Fig. 2: Seasonal Antarctic total sea ice extent comparisons, 1905–2020.
Fig. 3: Time-varying linear trends of standardized seasonal Antarctic total sea ice extent.
Fig. 4: Austral winter (JJA) sea ice extent reconstructions by sector.
Fig. 5: Changes in 2-year average seasonal sea ice extent.

Data availability

The reconstructions and the sea ice observations used to create them are all available on figshare59 at Soon after publication, the sea ice extent reconstructions will also be made available through the NSIDC.

Code availability

The reconstruction and all figures were generated using the NCAR Command Language. All code used to generate the figures in this paper is available in the Antarctic Sea Ice collection on figshare at


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All authors acknowledge support from the National Science Foundation Office of Polar Programs. R.L.F. and A.M.S. were supported by grant no. OPP-1744998, and M.N.R. and M.S.H. were supported by grant no. OPP-1745089.

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Authors and Affiliations



R.L.F., M.N.R. and M.S.H. conceived the study. R.L.F. and A.M.S. performed the reconstructions. R.L.F. led the writing of the manuscript and produced all the figures in the paper. All authors analysed the results and assisted in writing and editing the manuscript.

Corresponding author

Correspondence to Ryan L. Fogt.

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The authors declare no competing interests.

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Nature Climate Change thanks Sharon Stammerjohn, Elizabeth Thomas and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Map of predictor stations, additional climate index data layers, and sea ice sectors.

Sea ice sectors are defined as in Raphael and Hobbs (2014). Station data are primarily from the University Corporation for Atmospheric Research research data archive dataset ds570.0 (!description). See Methods for a more detailed description of data sources and sea ice sectors.

Extended Data Fig. 2 Boxplots of reconstruction performance.

Boxplots for reconstruction performance across all ensembles are in blue, and the best fit reconstruction for each sector, including total are in red. The vertical lines extend to the minimum and maximum for each skill metric, and the boxes extend to the upper and lower quartiles. The median for each distribution is given with the horizontal line in the middle of each boxplot.

Extended Data Fig. 3 Changes in year-to-year seasonal sea ice extent.

Seasonal probability density functions (PDF, in %) for differences (following year minus preceding year) in consecutive one year values in observed Antarctic total sea ice extent (black, plotted as a bar chart) and in all Antarctic total sea ice extent ensemble members from 1979–2020 (red) and 1905–2020 (blue). The dashed vertical lines indicate the minimum and maximum differences in observations, with the years corresponding to these record differences given in the upper corners within each panel.

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Fogt, R.L., Sleinkofer, A.M., Raphael, M.N. et al. A regime shift in seasonal total Antarctic sea ice extent in the twentieth century. Nat. Clim. Chang. 12, 54–62 (2022).

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