Attribution of Extreme Heatwave Events to Anthropogenic Climate Forcing
DOI:
https://doi.org/10.5281/zenodo.22794292Keywords:
extreme event attribution, heatwave, anthropogenic climate forcing, probability ratio, climate model large ensembles, counterfactual climate, fraction of attributable risk, July 2022 heatwaveAbstract
On 19 July 2022 the United Kingdom recorded a national maximum temperature of 40.3 degrees C for the first time,
part of a wider heatwave that affected England, northern France and the Low Countries over 18-19 July. We applied
probabilistic extreme event attribution to this episode, comparing the observed likelihood of an area-averaged daily
maximum temperature exceeding the 2022 threshold over England against its likelihood in a physically consistent
counterfactual world without anthropogenic forcing. Five CMIP6-generation single-model initial-condition large
ensembles (HadGEM3-GC31-LL, CESM2, EC-Earth3, CNRM-CM6-1 and CanESM5), each run under both
all-forcing historical-to-present and natural-only forcing, were combined with a generalised extreme value
distribution fitted to 1961-2022 HadUK-Grid station-gridded observations using smoothed global mean surface
temperature as a covariate. Across the five model ensembles, the probability ratio for equalling or exceeding the
observed threshold ranged from 19 to 71, with a multi-model synthesis estimate of 39 (95% confidence interval
10-190) and an independent observation-based estimate of 28 (7-140), indicating that anthropogenic forcing has
made an event of this magnitude at least an order of magnitude more likely than in the pre-industrial climate, with
the true factor plausibly exceeding one hundred. The associated shift in peak-day temperature attributable to
anthropogenic forcing averaged 3.0 degrees C across models. Regional decomposition showed the attributable
probability ratio was largest over England (39) and smallest over the Iberian Peninsula (14), where a strong
pre-existing hot climatology compresses the statistical rarity of any given absolute threshold. All model ensembles
agreed on the sign and approximate magnitude of the anthropogenic influence despite disagreement in absolute
event rarity, a pattern consistent with previous rapid-attribution studies of comparable events. We discuss the
sensitivity of these estimates to model selection, the choice of counterfactual construction, and the compounding
role of dynamical circulation anomalies that current large ensembles do not attribute separately from
thermodynamic warming, and conclude that the July 2022 heatwave was overwhelmingly attributable to
human-caused climate change even after accounting for this structural uncertainty.
References
Stott PA, Stone DA, Allen MR (2004) Human contribution to the European heatwave of 2003. Nature 432:610-614. https://doi.org/10.1038/nature03089
Philip SY, Kew SF, van Oldenborgh GJ, Otto FEL, Vautard R, van der Wiel K, King A, Lott F, Arrighi J, Singh R, van Aalst M (2020) A protocol for probabilistic extreme event attribution analyses. Advances in Statistical Climatology, Meteorology and Oceanography 6(2):177-203. https://doi.org/10.5194/ascmo-6-177-2020
National Academies of Sciences, Engineering, and Medicine (2016) Attribution of Extreme Weather Events in the Context of Climate Change. Washington, DC: The National Academies Press. https://doi.org/10.17226/21852
Trenberth KE, Fasullo JT, Shepherd TG (2015) Attribution of climate extreme events. Nature Climate Change 5:725-730. https://doi.org/10.1038/nclimate2657
Seneviratne SI, Zhang X, Adnan M, Badi W, Dereczynski C, Di Luca A, Ghosh S, Iskandar I, Kossin J, Lewis S, Otto F, Pinto I, Satoh M, Vicente-Serrano SM, Wehner M, Zhou B (2021) Weather and Climate Extreme Events in a Changing Climate. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the IPCC. https://doi.org/10.1017/9781009157896.013
Otto FEL, Massey N, van Oldenborgh GJ, Jones RG, Allen MR (2012) Reconciling two approaches to attribution of the 2010 Russian heat wave. Geophysical Research Letters 39(4):L04702. https://doi.org/10.1029/2011GL050422
Vautard R, van Oldenborgh GJ, Otto FEL, Yiou P, de Vries H, van Meijgaard E, Stepek A, Soubeyroux JM, Philip S, Kew SF, Costella C, Singh R, Tebaldi C (2020) Human contribution to the record-breaking June 2019 heat wave in France. Environmental Research Letters 15(9):094077. https://doi.org/10.1088/1748-9326/aba3d4
Ciavarella A, Cotterill D, Stott P, Kew S, Philip S, van Oldenborgh GJ, Skalevag A, Lorenz P, Robin Y, Otto F, Hauser M, Seneviratne SI, Lehner F, Zolina O (2021) Prolonged Siberian heat of 2020 almost impossible without human influence. Climatic Change 166(1-2):9. https://doi.org/10.1007/s10584-020-02879-4
Thompson V, Kennedy-Asser AT, Vosper E, Lo YTE, Huntingford C, Andrews O, Collins M, Hegerl GC, Mitchell D (2022) The 2021 western North America heat wave among the most extreme events ever recorded by any metric. Science Advances 8(18):eabm6860. https://doi.org/10.1126/sciadv.abm6860
Philip SY, Kew SF, van Oldenborgh GJ, Anslow FS, Seneviratne SI, Vautard R, Coumou D, Ebi KL, Arrighi J, Singh R, van Aalst M, Pereira Marghidan C, Wehner M, Yang W, Li S, Schumacher DL, Zscheischler J, Hauser M, Otto FEL (2022) Rapid attribution analysis of the extraordinary heatwave on the Pacific coast of the US and Canada in June 2021. Earth System Dynamics 13(4):1689-1713. https://doi.org/10.5194/esd-13-1689-2022
Barriopedro D, Fischer EM, Luterbacher J, Trigo RM, Garcia-Herrera R (2011) The hot summer of 2010: redrawing the temperature record map of Europe. Science 332(6026):220-224. https://doi.org/10.1126/science.1201224
Russo S, Sillmann J, Fischer EM (2015) Top ten European heatwaves since 1950 and their occurrence in the coming decades. Environmental Research Letters 10(12):124003. https://doi.org/10.1088/1748-9326/10/12/124003
Fischer EM, Knutti R (2015) Anthropogenic contribution to global occurrence of heavy-precipitation and high-temperature extremes. Nature Climate Change 5:560-564. https://doi.org/10.1038/nclimate2617
Perkins-Kirkpatrick SE, Lewis SC (2020) Increasing trends in regional heatwaves. Nature Communications 11:3357. https://doi.org/10.1038/s41467-020-16970-7
Sippel S, Meinshausen N, Fischer EM, Szekely E, Knutti R (2020) Climate change now detectable from any single day of weather at global scale. Nature Climate Change 10:35-41. https://doi.org/10.1038/s41558-019-0666-7
Diffenbaugh NS, Singh D, Mankin JS, Horton DE, Swain DL, Touma D, Charland A, Liu Y, Haugen M, Tsiang M, Rajaratnam B (2017) Quantifying the influence of global warming on unprecedented extreme climate events. Proceedings of the National Academy of Sciences 114(19):4881-4886. https://doi.org/10.1073/pnas.1618082114
Vogel MM, Zscheischler J, Fischer EM, Seneviratne SI (2020) Development of future heatwaves for different hazard thresholds. Journal of Geophysical Research: Atmospheres 125(9):e2019JD032070. https://doi.org/10.1029/2019JD032070
Min SK, Zhang X, Zwiers FW, Hegerl GC (2011) Human contribution to more-intense precipitation extremes. Nature 470:378-381. https://doi.org/10.1038/nature09763
Bador M, Terray L, Boe J (2016) Emergence of human influence on summer record-breaking temperatures over Europe. Geophysical Research Letters 43(1):404-412. https://doi.org/10.1002/2015GL066560
Rahmstorf S, Coumou D (2011) Increase of extreme events in a warming world. Proceedings of the National Academy of Sciences 108(44):17905-17909. https://doi.org/10.1073/pnas.1101766108
Kew SF, Philip SY, van Oldenborgh GJ, van der Schrier G, Otto FEL, Vautard R (2019) The exceptional summer heat wave in southern Europe 2017. Bulletin of the American Meteorological Society 100(1):S49-S53. https://doi.org/10.1175/BAMS-D-18-0109.1
Kornhuber K, Osprey S, Coumou D, Petri S, Petoukhov V, Rahmstorf S, Gray L (2019) Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern. Environmental Research Letters 14(5):054002. https://doi.org/10.1088/1748-9326/ab13bf
Christidis N, Jones GS, Stott PA (2015) Dramatically increasing chance of extremely hot summers since the 2003 European heatwave. Nature Climate Change 5:46-50. https://doi.org/10.1038/nclimate2468
Eyring V, Bony S, Meehl GA, Senior CA, Stevens B, Stouffer RJ, Taylor KE (2016) Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization. Geoscientific Model Development 9(5):1937-1958. https://doi.org/10.5194/gmd-9-1937-2016
Deser C, Lehner F, Rodgers KB, Ault T, Delworth TL, DiNezio PN, Fasullo J, Garcia-Serrano J, Hausfather Z, Karnauskas KB, Meehl GA, Middlemas E, Rushley S, Suarez-Gutierrez L, Wittenberg AT (2020) Insights from Earth system model initial-condition large ensembles and future prospects. Nature Climate Change 10:277-286. https://doi.org/10.1038/s41558-020-0731-2
Wehner M, Stone D, Krishnan H, AchutaRao K, Castillo F (2016) The deadly combination of heat and humidity in India and Pakistan in summer 2015. Bulletin of the American Meteorological Society 97(12):S81-S86. https://doi.org/10.1175/BAMS-D-16-0145.1
Perkins-Kirkpatrick SE, Gibson PB (2017) Changes in regional heatwave characteristics as a function of increasing global temperature. Scientific Reports 7:12256. https://doi.org/10.1038/s41598-017-12520-2
van Oldenborgh GJ, van der Wiel K, Sebastian A, Singh R, Arrighi J, Otto F, Haustein K, Li S, Vecchi G, Cullen H (2017) Attribution of extreme rainfall from Hurricane Harvey, August 2017. Environmental Research Letters 12(12):124009. https://doi.org/10.1088/1748-9326/aa9ef2
