Widespread impacts and insights contrasted between extreme North American heatwaves in 1941 and 2021

The 2021 Western North American heatwave was among the most extreme events ever recorded and irreversibly impacted physical and social systems. However, recent work has identified an event of comparable magnitude and geographic extent in 1941. Despite its importance for contextualizing one of the most highly studied 21st century heatwaves, very little is known about the impacts of this “forgotten” heatwave of 1941. Here, we review 357 newspaper issues from 25 North American publications from before, during, and after the 1941 heatwave, and provide a quantitative analysis of climate reanalysis, streamflow, tidal, and crop yield data. We uncover widespread impacts including record-shattering temperature observations, water shortages, crop damages, wildfires, flooding, human mortality and morbidity, as well as adaptation via changes to social customs, behaviours, and mobility. We compare with 2021 and find key differences including the continental-scale heatwave evolution, which propagated to Eastern North America in 1941, but not 2021, and the heatwaves’ relation to co-occurring crises of World War II and the COVID-19 pandemic. The 1941 event provides vital context for future heatwaves that would be missed if 2021 is used as the sole reference for what is possible during extreme heat in Western North America.