Unprecedented 21st century heat across the Pacific Northwest of North America

Extreme summer temperatures are increasingly common across the Northern Hemisphere and inflict severe socioeconomic and biological consequences. In summer 2021, the Pacific Northwest region of North America (PNW) experienced a 2-week-long extreme heatwave, which contributed to record-breaking summer temperatures. Here, we use tree-ring records to show that summer temperatures in 2021, as well as the rate of summertime warming during the last several decades, are unprecedented within the context of the last millennium for the PNW. In the absence of committed efforts to curtail anthropogenic emissions below intermediate levels (SSP2-4.5), climate model projections indicate a rapidly increasing risk of the PNW regularly experiencing 2021-like extreme summer temperatures, with a 50% chance of yearly occurrence by 2050. The 2021 summer temperatures experienced across the PNW provide a benchmark and impetus for communities in historically temperate climates to account for extreme heat-related impacts in climate change adaptation strategies.

Automated summary

In the summer of 2021, the Pacific Northwest region of North America experienced a two-week-long extreme heatwave, breaking historical records. Tree-ring records indicate that summer temperatures in 2021, as well as the rate of warming in recent decades, are unprecedented in the past thousand years for the PNW. Without efforts to reduce anthropogenic emissions, climate models project a rapidly increasing risk of regular occurrence of extreme summer temperatures similar to 2021 in the PNW, with a 50% chance of yearly occurrence by 2050. The 2021 summer temperatures serve as a benchmark and motivation for communities in historically temperate climates to include extreme heat impacts in their climate change adaptation strategies.