Incoming Northwest heatwave 5x more likely due to climate change

Temperatures on Sunday and Monday could hit 90 degrees in Seattle, about 20 degrees above normal, according to the National Weather Service.

In Olympia, Washington, temperatures are forecast to go 25 degrees above normal, defined as the 30-year average from 1991-2020.

To the north, parts of British Columbia are forecast to hit 27 degrees above normal.

Heatwaves are nothing new, but temperatures like these are far outside the norm for May in the temperate, coastal Northwest. On Friday, Sea-Tac Airport, Seattle’s official weather station, notched its warmest May 12 in history when it hit 82 degrees.

One-third of the years since 1945 have had an 85-degree day in May, according to assistant Washington State Climatologist Karin Bumbaco. Only six Mays on record in Seattle have had 90-degree days.

Climate scientist Andrew Pershing with the nonprofit Climate Central in Princeton, New Jersey, says human-driven climate change is making heatwaves like the one now building over the Pacific Northwest and western Canada much more likely.

“Many places in the Pacific Northwest from Washington up into British Columbia are going to experience conditions [over the next few days] that are at least five times more likely due to climate change,” Pershing said.

As the atmosphere’s carbon dioxide concentrations, boosted primarily by fossil-fuel use and deforestation, continue to rise, heatwaves are expected to arrive more frequently and become longer and more extreme.

The heat expected for the coming days falls well short of the triple-digit temperatures that killed an estimated 1,200 people in British Columbia, Oregon, and Washington in late June and early July 2021.

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A less-severe heatwave in July 2022 killed at least 24 people in Washington and Oregon and sent 544 people to emergency rooms in Washington.

Scientists say the Northwest’s imminent heatwave, even with temperatures barely hitting 90, is likely to be enough to kill vulnerable people, especially in a region where many homes lack air conditioning.

“These heat events that happen early in the year, before people have had a chance to get into summer mode and adjust to it, can actually be quite stressful for people and can lead to extra mortality, especially for people who have health that's otherwise stressed,” Pershing said.

Health-care experts say heat deaths are preventable, especially with better support systems for the most vulnerable, including the very old, the very young, and people who work or live outdoors.

King County, home to Seattle, is opening up air-conditioned cooling centers for people needing a place to beat the heat.

Six of eight indoor pools operated by Seattle’s parks department will be open over the weekend, though many outdoor pools and spray parks will not open until late May or late June. Some are not slated to open at all this year.

The Seattle parks department blames a nationwide shortage of lifeguards.