Can natural variability explain observed Antarctic sea ice trends? New modeling evidence from CMIP5

Authors

  • Lorenzo M. Polvani,

    1. Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, New York, USA
    2. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Palisades, New York, USA
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  • Karen L. Smith

    Corresponding author
    1. Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Palisades, New York, USA
    • Corresponding author: K. L. Smith, Division of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, 61 Rt. 9W, PO Box 1000, Palisades, NY 10964, USA. (ksmith@ldeo.columbia.edu)

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Abstract

[1] The recent observed positive trends in total Antarctic sea ice extent are at odds with the expectation of melting sea ice in a warming world. More problematic yet, climate models indicate that sea ice should decrease around Antarctica in response to both increasing greenhouse gases and stratospheric ozone depletion. The resolution of this puzzle, we suggest, may lie in the large natural variability of the coupled atmosphere‒ocean‒sea‒ice system. Contrasting forced and control integrations from four state‒of‒the‒art Coupled Model Intercomparison Project Phase 5 (CMIP5) models, we show that the observed Antarctic sea ice trend falls well within the distribution of trends arising naturally in the system, and that the forced response in the models is small compared to the natural variability. From this, we conclude that it may prove difficult to attribute the observed trends in total Antarctic sea ice to anthropogenic forcings, although some regional features might be easier to explain.

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