Skip to main content
U.S. flag

An official website of the United States government

Publication Date
16 November 2022

Anthropogenic contributions to the 2021 Pacific Northwest heatwave



Daily maximum temperatures during the 2021 heatwave in the Pacific Northwest United States and Canada shattered century old records. Multiple causal factors, including anthropogenic climate change, contributed to these high temperatures, challenging traditional methods of attributing human influence. We demonstrate that the observed 2021 daily maximum temperatures are far above the bounds of Generalized Extreme Value distributions fitted from historical data. Hence, confidence in Granger causal inference statements about the human influence on this heatwave is low. Alternatively, we present a more conditional hindcast attribution study using two regional models. We performed ensembles of simulations of the heatwave to investigate how the event would have changed if it had occurred without anthropogenic climate change and with future warming. We found that global warming caused a ∼0.8-1°C increase in heatwave temperatures. Future warming would lead to a ∼5°C increase in heatwave temperature by the end of the 21st century. 

Bercos‐Hickey, Emily, Travis A. O’Brien, Michael F. Wehner, Likun Zhang, Christina M. Patricola, Huanping Huang, and Mark D. Risser. 2022. “Anthropogenic Contributions To The 2021 Pacific Northwest Heatwave”. Geophysical Research Letters 49. American Geophysical Union (AGU). doi:10.1029/2022gl099396.
Funding Program Area(s)
Additional Resources:
NERSC (National Energy Research Scientific Computing Center)