A Regime Shift in Seasonal Total Antarctic Sea Ice Extent in the 20th Century

Abstract

In stark contrast to the Arctic, there have been statistically significant positive trends in total Antarctic sea ice extent since 1979, despite a sudden decline in sea ice in 2016(1–5) and increasing greenhouse gas concentrations. Attributing Antarctic sea ice trends is complicated by the fact that most coupled climate models show negative trends in sea ice extent since 1979, opposite of that observed(6–8). Additionally, the short record of sea ice extent (beginning in 1979), coupled with the high degree of interannual variability, make the record too short to fully understand the historical context of these recent changes(9). Here we show, using new robust observation-based reconstructions, that 1) these observed recent increases in Antarctic sea ice extent are unique in the context of the 20th century and 2) the observed trends are juxtaposed against statistically significant decreases in sea ice extent throughout much of the early and middle 20th century. These reconstructions are the first to provide reliable estimates of total sea ice extent surrounding the continent; previous proxy-based reconstructions are limited(10). Importantly, the reconstructions continue to show the high degree of interannual Antarctic sea ice extent variability that is marked with frequent sudden changes, such as observed in 2016, which stress the importance of a longer historical context when assessing and attributing observed trends in Antarctic climate(9). Our reconstructions are skillful enough to be used in climate models to allow better understanding of the interconnected nature of the Antarctic climate system and to improve predictions of the future state of Antarctic climate.

An Unprecedented Sea Ice Retreat in the Weddell Sea Driving an Overall Decrease of the Antarctic Sea‐Ice Extent Over the 20th Century

“…Sea-ice concentration data set from the NSIDC is freely available (NSIDC, 2023). Regional reconstructions of sea-ice extent of Fogt et al (2022) is publicly available (Fogt et al, 2023). The Marshall index is stored on the British Antarctic Survey website (G. .…”

“…Regional reconstructions of sea‐ice extent of Fogt et al. (2022) is publicly available (Fogt et al., 2023). The Marshall index is stored on the British Antarctic Survey website (G. Marshall, 2003).…”

A Comparison of South Pacific Antarctic Sea Ice and Atmospheric Circulation Reconstructions Since 1900

“…The Fogt et al (2022a) sea ice reconstructions can be obtained from the National Snow and Ice Data Ceter dataset G10039 (https://nsidc.org/data/g10039/versions/1) (Fogt et al, 2023). The…”