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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-2020-40
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-40
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  28 Aug 2020

28 Aug 2020

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This preprint is currently under review for the journal WCD.

Global warming makes weather in boreal summer more persistent

Dim Coumou1,2, and Paolo De Luca1, Dim Coumou and Paolo De Luca
  • 1Department of Water and Climate Risk, Institute for Environmental Studies (IVM), Vrije Universiteit Amsterdam, Amsterdam, 1081 HV, the Netherlands
  • 2Royal Netherlands Meteorological Institute (KNMI), De Bilt, 3730 AE, the Netherlands
  • These authors contributed equally to the work.

Abstract. Extreme summer weather often has devastating impacts on society when it lasts for many days. Stalling cyclones can lead to flooding and persistent hot-dry conditions can lead to health impacts and harvest losses. Global warming weakens the hemispheric-wide circulation in boreal summer, which has been shown in both observations and models using multiple circulation metrics. Until now, it is still largely unclear what this weakening implies for regional weather conditions, including their persistence. Using an advanced persistence metric, we show that summer weather has become more-persistent over 1979–2019. State-of-the-art climate models reproduce this upward trend in persistence indicating that it can be attributed to greenhouse gas forcing. Our persistence metric accounts for the full state of the atmosphere at any given moment and is strongly rooted in dynamical systems theory. Thereby it is able to detect dynamical changes previously unseen in more widely used clustering analyses that sharply reduce the amount of information used. We show that under future high-emission scenarios, summer weather will become increasingly more-persistent due to a weakening of the circulation. Most of this increase in persistence, and the associated societal risks, is avoided under an emission scenario compatible with the Paris agreement.

Dim Coumou and Paolo De Luca

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Dim Coumou and Paolo De Luca

Dim Coumou and Paolo De Luca

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Latest update: 24 Sep 2020
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Short summary
We show that the persistence of summer weather has increased throughout the mid-latitudes over the last 40 years, in both observations and CMIP6 models. Our results provide solid evidence that the weakening of the summer jet-stream has already made weather more persistent. We also show that future greenhouse-gases emissions will further increase weather persistence, creating risks from high-impact, stalling weather extremes like persistent heat waves and stalling cyclones.
We show that the persistence of summer weather has increased throughout the mid-latitudes over...
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