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Asymmetry in the seasonal cycle of Antarctic sea ice driven by insolation


The mean seasonal cycle of Antarctic sea-ice extent is asymmetric, with the period of ice retreat being approximately two months shorter than the period of ice advance. This feature is largely consistent in observations from year to year and across different satellite products. The asymmetry is also broadly reproduced by comprehensive climate models across generations from CMIP3 to CMIP6, with limited impacts from internal variability. Using a range of idealized climate models of varying complexity, we show that the seasonal cycle in top-of-atmosphere incident solar radiation drives the asymmetry. Because insolation in southern high latitudes departs from a sinusoid by having a narrow peak of intense brightness in summer and a long period of low light in winter, there is rapid summer ice retreat and gradual winter ice advance. This simple physical explanation is markedly different from those proposed in previous studies.

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Fig. 1: Observed mean seasonal cycle in Antarctic sea-ice extent averaged over 1979–1998.
Fig. 2: Antarctic sea-ice seasonal asymmetry (δI) in CMIP6 simulations and observations.
Fig. 3: Antarctic sea-ice extent and temperature seasonal asymmetry in a range of configurations of the idealized climate model.
Fig. 4: Insolation and resulting surface temperature in the simplest model configuration (NoIce_NoDiff).

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We thank C. Eayrs for helpful discussions. This work was supported by the Scientific Committee on Antarctic Research (SCAR) Fellowship Program; the National Oceanic and Atmospheric Administration (NOAA) Climate and Global Change Postdoctoral Fellowship Program, which is administered by UCAR’s Cooperative Programs for the Advancement of Earth System Science (CPAESS) under award NA18NWS4620043B; US National Science Foundation grants OPP-1643445, OCE-2048590 and OPP-1643431; and NOAA grant NA18OAR4310274.

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T.J.W.W. and L.A.R. conceived the study question. I.E., L.A.R. and T.J.W.W. designed the research, constructed the idealized models, interpreted the results and developed the conclusions. L.A.R. analysed the observations and CMIP output. C.M.B. and E.B.-W. assisted with initial attempts to address the question. L.A.R., I.E. and T.J.W.W. wrote the manuscript with contributions from all co-authors.

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Correspondence to I. Eisenman.

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Nature Geoscience thanks Clare Eayrs, Kenneth Golden and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Tom Richardson, in collaboration with the Nature Geoscience team.

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Roach, L.A., Eisenman, I., Wagner, T.J.W. et al. Asymmetry in the seasonal cycle of Antarctic sea ice driven by insolation. Nat. Geosci. 15, 277–281 (2022).

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