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Western heat wave was a 1 in 1,000-year event made more likely by climate change, study shows

UPDATED: Wed., July 7, 2021

The evening sun shines through a U.S. flag flying in the wind in Tacoma in this photo from 2019.  (Ted S. Warren)
The evening sun shines through a U.S. flag flying in the wind in Tacoma in this photo from 2019. (Ted S. Warren)

Last week’s heat wave, which led to record temperatures in the Pacific Northwest and subsequent wildfires, was a 1 in 1,000-year event, according to a new analysis from an international group of researchers.

The heat wave, the researchers concluded, “was virtually impossible without human-caused climate change.” Spokane, Omak, Wenatchee and Lewiston all broke records for the highest temperature recorded on June 30.

Early estimates show that 69 Washington residents have died in the heat wave, with medical examiners expecting a higher death toll in the coming weeks. Experts believe these deaths are preventable.

“In the United States, heat-related mortality is the number one weather-related killer, yet nearly all of those deaths are preventable,” Kristie Ebi, with the University of Washington, said in a news release. “Heat action plans can reduce current and future heat-related morbidity and mortality by increasing preparedness for heat emergencies, including heat wave early warning and response systems, and by prioritizing modifications to our built environment so that a warmer future does not have to be deadly.”

In Canada, record temperatures quickly turned into deadly wildfires, especially in places like Lytton, British Columbia, which was evacuated and decimated by the flames.

The analysis shows the Pacific Northwest heat wave was way outside the range of historically recorded temperatures, including in cities closer to the coast like Portland, Seattle and Vancouver, British Columbia.

Scientists believe there are two potential sources for the extreme heat wave: Either it was unusual and the statistical equivalent of bad luck, or the probability of such events has increased substantially with global warming, causing a faster rise in temperatures.

“While we expect heat waves to become more frequent and intense, it was unexpected to see such levels of heat in this region. It raises serious questions whether we really understand how climate change is making heat waves hotter and more deadly,” Geert Jan van Oldenborgh, from the Royal Netherlands Meteorological Institute, said in a news release.

The analysis estimates that the heat wave would have been 150 times rarer without climate change. As the earth warms, these events could occur more frequently.

“In summary, an event such as the Pacific Northwest 2021 heat wave is still rare or extremely rare in today’s climate, yet would be virtually impossible without human-caused climate change,” the study says. “As warming continues, it will become a lot less rare.”

Experts in climate science and meteorology from the United States, Canada and Europe contributed to the study.

Arielle Dreher's reporting for The Spokesman-Review is funded in part by Report for America and by members of the Spokane community. This story can be republished by other organizations for free under a Creative Commons license. For more information on this, please contact our newspaper’s managing editor.

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