Data-driven upper bounds and event attribution for unprecedented heatwaves

Journal Article · 30 January 2025 · Weather and Climate Extremes

DOI: https://doi.org/10.1016/j.wace.2025.100743 · OSTI ID:2510932

Risser, Mark D.  ^[1]; Zhang, Likun ^[2]; Wehner, Michael F. ^[1]

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1. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
2. Univ. of Missouri, Columbia, MO (United States)

The last decade has seen numerous record-shattering heatwaves in all corners of the globe. In the aftermath of these devastating events, there is interest in identifying worst-case thresholds or upper bounds that quantify just how hot temperatures can become. Generalized Extreme Value theory provides a data-driven estimate of extreme thresholds; however, upper bounds may be exceeded by future events, which undermines attribution and planning for heatwave impacts. Here, we show how the occurrence and relative probability of observed yet unprecedented events that exceed a priori upper bound estimates, so-called “impossible” temperatures, has changed over time. We find that many unprecedented events are actually within data-driven upper bounds, but only when using modern spatial statistical methods. Furthermore, there are clear connections between anthropogenic forcing and the “impossibility” of the most extreme temperatures. Robust understanding of heatwave thresholds provides critical information about future record-breaking events and how their extremity relates to historical measurements.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 2510932
• Journal Information: Weather and Climate Extremes, Journal Name: Weather and Climate Extremes Vol. 47; ISSN 2212-0947
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English