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<p>September 2023 featured an unprecedented temperature jump of nearly 0.6&#xa0;°C above September 2022. Although climate models hardly reproduce such an event, it remains unclear whether the extreme heat could have been caused by internal variability alone or how large an external contribution would be needed to render it plausible. Here we show, based on observational and climate model data, that the temperature jump was virtually impossible under standard anthropogenic forcing, but its probability increases to 0.1% when probabilistic attribution is combined with a process-based analysis to account for contributions that models may underrepresent. Our findings reveal that the heat was disproportionately concentrated over land, particularly in the extratropics. The event resulted from a complex interplay of feedbacks and forcings, with unusually high shortwave forcing amplified by water vapour feedback. Although extreme temperature jumps in September are projected to intensify gradually under additional warming, an internally driven jump of comparable magnitude remains highly unlikely during the next decades.</p>

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The observed September 2023 temperature jump was nearly impossible under standard anthropogenic forcing

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月10日

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  • Svenja Seeber,
  • Dominik L. Schumacher,
  • Lukas Gudmundsson,
  • Sonia I. Seneviratne

摘要

September 2023 featured an unprecedented temperature jump of nearly 0.6 °C above September 2022. Although climate models hardly reproduce such an event, it remains unclear whether the extreme heat could have been caused by internal variability alone or how large an external contribution would be needed to render it plausible. Here we show, based on observational and climate model data, that the temperature jump was virtually impossible under standard anthropogenic forcing, but its probability increases to 0.1% when probabilistic attribution is combined with a process-based analysis to account for contributions that models may underrepresent. Our findings reveal that the heat was disproportionately concentrated over land, particularly in the extratropics. The event resulted from a complex interplay of feedbacks and forcings, with unusually high shortwave forcing amplified by water vapour feedback. Although extreme temperature jumps in September are projected to intensify gradually under additional warming, an internally driven jump of comparable magnitude remains highly unlikely during the next decades.