Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends

Robert Vautard; Julien Cattiaux; Tamara Happé; Jitendra Singh; Rémy Bonnet; Christophe Cassou; Dim Coumou; Fabio D’Andrea; Davide Faranda; Erich Fischer; Aurélien Ribes; Sebastian Sippel; Pascal Yiou

doi:10.1038/s41467-023-42143-3

Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends

Robert Vautard^*, Julien Cattiaux, Tamara Happé, Jitendra Singh, Rémy Bonnet, Christophe Cassou, Dim Coumou, Fabio D’Andrea, Davide Faranda, Erich Fischer, Aurélien Ribes, Sebastian Sippel, Pascal Yiou

^*Corresponding author for this work

Water and Climate Risk

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Over the last 70 years, extreme heat has been increasing at a disproportionate rate in Western Europe, compared to climate model simulations. This mismatch is not well understood. Here, we show that a substantial fraction (0.8 °C [0.2°−1.4 °C] of 3.4 °C per global warming degree) of the heat extremes trend is induced by atmospheric circulation changes, through more frequent southerly flows over Western Europe. In the 170 available simulations from 32 different models that we analyzed, including 3 large model ensembles, none have a circulation-induced heat trend as large as observed. This can be due to underestimated circulation response to external forcing, or to a systematic underestimation of low-frequency variability, or both. The former implies that future projections are too conservative, the latter that we are left with deep uncertainty regarding the pace of future summer heat in Europe. This calls for caution when interpreting climate projections of heat extremes over Western Europe, in view of adaptation to heat waves.

Original language	English
Article number	6803
Pages (from-to)	1-9
Number of pages	9
Journal	Nature Communications
Volume	14
Early online date	26 Oct 2023
DOIs	https://doi.org/10.1038/s41467-023-42143-3
Publication status	Published - 2023

Bibliographical note

Funding Information:
This study was partly supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101003469 (XAIDA project). P.Y. was also supported by the grant ANR-20-CE01-0008-01 (SAMPRACE). The authors thank Dr. Efi Rousi for providing the sequences of dates of double-jet days. The authors also thank Atef Ben Nasser and the ESPRI IPSL data and computing service for their support in handling the large ensemble of climate simulations. The GMT v6.3 software is used for figure maps.

Publisher Copyright:
© 2023, The Author(s).

Funding

This study was partly supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101003469 (XAIDA project). P.Y. was also supported by the grant ANR-20-CE01-0008-01 (SAMPRACE). The authors thank Dr. Efi Rousi for providing the sequences of dates of double-jet days. The authors also thank Atef Ben Nasser and the ESPRI IPSL data and computing service for their support in handling the large ensemble of climate simulations. The GMT v6.3 software is used for figure maps.

Funders	Funder number
SAMPRACE
Agence Nationale de la Recherche	ANR-20-CE01-0008
European Union’s Horizon 2020 research and innovation programme	ANR-20-CE01-0008-01, 101003469

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title = "Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends",

abstract = "Over the last 70 years, extreme heat has been increasing at a disproportionate rate in Western Europe, compared to climate model simulations. This mismatch is not well understood. Here, we show that a substantial fraction (0.8 °C [0.2°−1.4 °C] of 3.4 °C per global warming degree) of the heat extremes trend is induced by atmospheric circulation changes, through more frequent southerly flows over Western Europe. In the 170 available simulations from 32 different models that we analyzed, including 3 large model ensembles, none have a circulation-induced heat trend as large as observed. This can be due to underestimated circulation response to external forcing, or to a systematic underestimation of low-frequency variability, or both. The former implies that future projections are too conservative, the latter that we are left with deep uncertainty regarding the pace of future summer heat in Europe. This calls for caution when interpreting climate projections of heat extremes over Western Europe, in view of adaptation to heat waves.",

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Heat extremes in Western Europe increasing faster than simulated due to atmospheric circulation trends

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