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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/wcd-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-29
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Jul 2020

27 Jul 2020

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This preprint is currently under review for the journal WCD.

The role of Arctic sea ice loss in projected polar vortex changes

Marlene Kretschmer1, Giuseppe Zappa1,2, and Theodore G. Shepherd1 Marlene Kretschmer et al.
  • 1Department of Meteorology, University of Reading, Reading, UK
  • 2Istituto di Scienze dell'Atmosfera e del Clima, Consiglio Nazionale delle Ricerche, Bologna, Italy

Abstract. The Northern Hemisphere stratospheric polar vortex (SPV) plays a key role for mid-latitude weather and climate. However, in what way the SPV will respond to global warming is not clear, with climate models disagreeing on the sign and magnitude of projected SPV strength change. Here we address the role of Barents and Kara (BK) sea ice loss in this. We provide evidence for a non-linear response of the SPV to global mean temperature change, dependent on the time the BK Seas become ice-free. Using a causal network approach, we demonstrate that climate models show some partial support for the previously proposed link between low BK sea ice in autumn and a weakened winter SPV, but that this effect is plausibly very small relative to internal variability. Yet, given the expected dramatic decrease of sea ice in the future, a small causal effect can explain all of the projected ensemble-mean SPV weakening, approximately one-half of the ensemble spread at the middle of the 21st century, and one-third of the spread at the end of the century. Finally, we note that most models have unrealistic amounts of BK sea ice, meaning that their SPV response to ice loss is unrealistic. Bias-adjusting for this effect leads to pronounced differences in SPV response of individual models at both ends of the spectrum, but has no strong consequences for the overall ensemble mean and spread. Overall, our results indicate the importance of exploring all plausible implications of a changing Arctic for regional climate risk assessments.

Marlene Kretschmer et al.

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Marlene Kretschmer et al.

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Latest update: 09 Aug 2020
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Short summary
The so-called stratospheric polar vortex affects the weather in the mid-latitudes making it important to understand potential changes in response to global warming. However, climate model projections disagree on how the vortex will change in the future. Here we show that sea ice loss in the Barents and Kara (BK) Seas plays a central role in this. The time the BK Seas are ice-free yet differs between models which explains some of the the disagreement regarding the polar vortex projections.
The so-called stratospheric polar vortex affects the weather in the mid-latitudes making it...
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