Tree rings confirm historic extremity of 2021 western North America heat wave.

A new study of tree rings from the Pacific Northwest region shows that the 2021 heat wave was almost certainly the worst in at least the past millennium. The research established a year-by-year record of summer average temperatures going back to the year 950. The last 40 years, driven by human-influenced warming, has been the hottest—and that 2021 was the hottest summer in the entire span. The study suggests that no region is impervious to the economic and biological impacts of increasing summer temperatures, and communities across the world that have not been historically exposed to extreme heat are likely to experience greater morbidity and mortality.