Four graphs from the paper showing temperature trends and probability of heat events.
The top panels show trends of daily maximum temperature for 3 days per global mean temperature in weather stations (with different record lengths, based on availability) across the Pacific Northwest region in the period of June 15 to July 15. The panels represent the (a) 50th, (b) 95th percentiles and the (c) difference between the 95th and 50th percentiles. Circles represent statistically significant trends, pentagons represent trends (or trend differences) that are not statistically significant. Panel (d) shows in blue the probability of the heat events exceeding the historical 99th percentile in the large ensemble of the Community Earth System Model version 2 (CESM2) in historical (until 2014) and a future simulation using a regional rivalry scenario. The black line represents the 11-year running mean. The red line in panel (d) represents the probability of exceeding the historical maximum in the simulation. Credit: McKinnon and Simpson [2022], Figure 3
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Geophysical Research Letters

The 2021 Pacific Northwest heatwave was an exceptional event affecting most of western North America in late June to mid-July 2021. The temperatures reached were very high and led to many deaths in both the United States and Canada.

McKinnon and Simpson [2022] explore how unexpected that event was using both observations from weather stations across the region, as well as output from a large-ensemble (many simulations) of a global climate model (Community Earth System Model version 2) in historical conditions and one future climate scenario (ssp370, a regional rivalry scenario). They showed that in the Pacific Northwest the observed maximum temperatures in the summertime are not increasing faster than the mean. Furthermore, the climate model can simulate similar extreme events in the region, but these are rare.

In future projections, the most extreme temperature events in that region are increasing faster than the mean, which could lead to more frequent extreme events in the future.

Citation: McKinnon, K. A., & Simpson, I. R. (2022). How unexpected was the 2021 Pacific Northwest heatwave? Geophysical Research Letters, 49, e2022GL100380.

—Suzana Camargo, Editor, Geophysical Research Letters

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