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Publication Date
22 August 2023

Storylines for Unprecedented Heatwaves Based on Ensemble Boosting

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We use ensemble boosting, a new technique to find the most extreme heatwaves possible in a computationally efficient manner, to develop storylines of how hot heatwaves can get in a given place.


Through ensemble boosting, we find even more extreme events than in the normal CESM1 ensemble; some also exceed recently observed events, attesting to the fit-for-purpose of climate models. This method provides estimates of worst-case heatwaves that allow cities to plan for them. We cannot predict when the heat waves will occur, but we can show what is physically plausible. We call on the community to scrutinize the new method to strengthen the results and make them actionable.


Recent temperature extremes have shattered previously observed records, reaching intensities that were inconceivable before the events. Could the possibility of an event with such unprecedented intensity as the 2021 Pacific Northwest heatwave have been foreseen based on climate model information available before the event? Could the scientific community have quantified its potential intensity based on the current generation of climate models? The new technique generates physically plausible storylines of a heatwave hotter than observed in the Pacific Northwest. We also show that heatwaves of much greater intensities than ever observed are possible in other locations like the Greater Chicago and Paris regions. To establish confidence in storylines of ‘black swan’-type events, different lines of evidence need to be combined along with process understanding to make this information robust and actionable for stakeholders.

Point of Contact
Flavio Lehner
National Center for Atmospheric Research (NCAR)
Funding Program Area(s)
Storylines for unprecedented heatwaves based on ensemble boosting
Fischer, E. M., U. Beyerle, L. Bloin-Wibe, C. Gessner, V. Humphrey, F. Lehner, A. G. Pendergrass, S. Sippel, J. Zeder, and R. Knutti. 2023. “Storylines For Unprecedented Heatwaves Based On Ensemble Boosting”. Nature Communications 14 (1). Springer Science and Business Media LLC. doi:10.1038/s41467-023-40112-4.