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.
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Figure 1 and its base maps were created using the Python packages Matplotlib52 and Basemap. Sea-ice extent data in Fig. 1 are pre-calculated monthly extent values from the .csv files in version 3 from https://nsidc.org/data/g02135 that are qualitatively comparable to the quality-controlled files that end in December 2018 (ref. 53). We have supplemented these with the near-real-time product available at the NOAA Climate Data Record of Passive Microwave Sea Ice Concentration54, available at the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, and on the NSIDC website at https://nsidc.org/data/g02202/versions/3 and https://nsidc.org/data/g10016 (near-real-time data). The SAM Index55 was accessed at https://legacy.bas.ac.uk/met/gjma/sam.html.
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C.E. and D.M.H. were supported by the Center for Global Sea Level Change of NYU Abu Dhabi Research Institute (G1204) in the UAE and NSF PLR-1739003. This is ITGC contribution no. 0040. M.N.R. was supported by the National Science Foundation, Office of Polar Programs (grant no. NSF-OPP-1745089). X.L. was supported by the National Key R&D Program for Developing Basic Sciences (2018YFA0605703), the National Natural Science Foundation of China (grant 41676190) and the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDA19070202).
The authors declare no competing interests.
Peer review information Nature Geoscience thanks Ted Maksym, Xiaojun Yuan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: James Super.
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Eayrs, C., Li, X., Raphael, M.N. et al. Rapid decline in Antarctic sea ice in recent years hints at future change. Nat. Geosci. 14, 460–464 (2021). https://doi.org/10.1038/s41561-021-00768-3
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