Heatwaves Similar to the Unprecedented One in Summer 2021 Over Western North America Are Projected to Become More Frequent in a Warmer World

• Published in: Earth's future 2023-02, Vol.11 (2), p.n/a
• Main Authors: Dong, Zizhen, Wang, Lin, Xu, Peiqiang, Cao, Jie, Yang, Ruowen
• Format: Article
• Language: English
• Subjects: America; Climate; Climate change; CMIP; Emission; Emissions; extremes; Global warming; Heat waves; heatwave; Mountains; Temperature; Temperature extremes
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2022EF003437

Western North America (WNA) experienced an unprecedented heatwave from late June to early July 2021, which lies far outside the historical range. Based on the model outputs from Coupled Model Intercomparison Project Phase 6, we find that the likelihood of a heatwave over WNA similar to the 2021 one increases with global warming. Such a heatwave is projected to occur more frequently with increased extreme temperature and shortened return period. It means that a rare event in the current climate will be a more common event in a warmer climate, especially under a high‐emission scenario like the Shared Socioeconomic Pathways 585 (SSP5‐8.5). Moreover, we show a large expansion of areas over WNA that will break the 2021 record in the future with an increasing level of emission scenario. Nevertheless, some heatwave records west of the Rocky Mountains are still difficult to break, highlighting the specific extremity of the 2021 WNA heatwave. Plain Language Summary An unprecedented heatwave occurred across Western North America (WNA) from late June to early July 2021. It lies far outside the historical range and poses considerable hazards to the regional society and economy, raising questions about how the likelihood of a similar heatwave to the 2021 one will change under global warming. Here, we analyze the likelihood of experiencing a similar heatwave over WNA in a warmer world using 15 state‐of‐the‐art climate models that participate in the Coupled Model Intercomparison Project Phase 6 in different emission scenarios. We show that the likelihood of a similar event will increase in the future if the global warming level continues to rise. We also show that heatwaves similar to the unprecedented 2021 one over WNA are projected to become more frequent in the future, especially under the high‐emission scenario. Despite the increase in the likelihood of a similar event in the future, some temperature records west of the Rocky Mountains set in the 2021 summer are difficult to break regardless of the emission scenarios, illustrating the magnitude of heat extremes observed in 2021. Key Points An unprecedented heatwave lying far outside the historical range occurred from late June to early July 2021 over Western North America (WNA) The likelihood of experiencing a similar heatwave will diversely increase in a warmer world under different emission scenarios The heatwave‐affected areas over WNA that surpass the 2021 record will expand with global warming