Kais Bothe relaxes in the cool in the city hall pool, as temperatures hit 37 degrees Celsius (98.6 Fahrenheit) in Edmonton, Alberta, on June 30. (Jason Franson/The Canadian Press via AP, file)

Kais Bothe relaxes in the cool in the city hall pool, as temperatures hit 37 degrees Celsius (98.6 Fahrenheit) in Edmonton, Alberta, on June 30. (Jason Franson/The Canadian Press via AP, file)

Study: Northwest heat wave impossible without climate change

In Oregon alone, the state medical examiner reported 116 deaths related to the extreme hot weather.

By Seth Borenstein/ Associated Press

The deadly heat wave that roasted the Pacific Northwest and western Canada was virtually impossible without human-caused climate change that added a few extra degrees to the record-smashing temperatures, a new quick scientific analysis found.

An international team of 27 scientists calculated that climate change increased chances of the extreme heat occurring by at least 150 times, but likely much more.

The study, not yet peer reviewed, said that before the industrial era, the region’s late June triple-digit heat was the type that would not have happened in human civilization. And even in today’s warming world, it said, the heat was a once-in-a-millennium event.

But that once-in-a-millennium event would likely occur every five to 10 years once the world warms another 1.4 degrees, said Wednesday’s study from World Weather Attribution. That much warming could be 40 or 50 years away if carbon pollution continues at its current pace, one study author said.

This type of extreme heat “would go from essentially virtually impossible to relatively commonplace,” said study co-author Gabriel Vecchi, a Princeton University climate scientist. “That is a huge change.”

The study also found that in the Pacific Northwest and Canada climate change was responsible for about 3.6 degrees of the heat shock. Those few degrees make a big difference in human health, said study co-author Kristie Ebi, a professor at the Center for Health and the Global Environment at the University of Washington.

“This study is telling us climate change is killing people,” said Ebi, who endured the blistering heat in Seattle. She said it will be many months before a death toll can be calculated from June’s blast of heat but it’s likely to be hundreds or thousands. “Heat is the No. 1 weather-related killer of Americans.”

In Oregon alone, the state medical examiner on Wednesday reported 116 deaths related to the heat wave.

The team of scientists used a well-established and credible method to search for climate change’s role in extreme weather, according to the National Academy of Sciences. They logged observations of what happened and fed them into 21 computer models and ran numerous simulations. They then simulated a world without greenhouse gases from the burning of coal, oil and natural gas. The difference between the two scenarios is the climate change portion.

“Without climate change this event would not have happened,” said study senior author Friederike Otto, a climate scientist at the University of Oxford.

In this July 1 photo, a wildfire burns in the mountains north of Lytton, British Columbia, Canada, during record high temperatures. (Darryl Dyck/The Canadian Press via AP, File)

In this July 1 photo, a wildfire burns in the mountains north of Lytton, British Columbia, Canada, during record high temperatures. (Darryl Dyck/The Canadian Press via AP, File)

What made the Northwest heat wave so remarkable is how much hotter it was than old records and what climate models had predicted. Scientists say this hints that some kind of larger climate shift could be in play — and in places that they didn’t expect.

“Everybody is really worried about the implications of this event,” said study co-author Geert Jan van Oldenborgh, a Dutch climate scientist. “This is something that nobody saw coming, that nobody thought possible. And we feel that we do not understand heat waves as well as we thought we did. The big question for many people is: Could this also happen in a lot of places?”

The World Weather Attribution team does these quick analyses, which later get published in peer-reviewed journals. In the past, they have found similar large climate change effects in many heat waves, including ones in Europe and Siberia. But sometimes the team finds climate change wasn’t a factor, as they did in a Brazilian drought and a heat wave in India.

Six outside scientists said the quick study made sense and probably underestimated the extent of climate change’s role in the heat wave.

That’s because climate models used in the simulations usually underestimate how climate change alters the jet stream that parks “heat domes” over regions and causes some heat waves, said Pennsylvania State University climate scientist Michael Mann.

The models also underestimate how dry soil worsens heat because there is less water to evaporate, which feeds a vicious cycle of drought, said Daniel Swain, a climate scientist at UCLA and the Nature Conservancy.

The study hit home for University of Victoria climate scientist Andrew Weaver, who wasn’t part of the research team.

“Victoria, which is known for its mild climate, felt more like Death Valley last week,” Weaver said. “I’ve been in a lot of hot places in the world, and this was the worst I’ve ever been in.

“But you ain’t seen nothing yet,” he added. “It’s going to get a lot worse.”

Talk to us

> Give us your news tips.

> Send us a letter to the editor.

> More Herald contact information.

More in Northwest

A classroom inside College Place Middle School in Lynnwood in 2023. New discipline guidelines for public school students will go into effect across Washington state next month. (Annie Barker / The Herald)
Washington updates student discipline rules for public schools

New discipline guidelines for public school students will go into effect across… Continue reading

The Northwest ICE Processing Center in Tacoma, which is one of the largest immigrant detention facilities in the western U.S. (Grace Deng/Washington State Standard)
WA looks to strengthen safety net for children whose parents are deported

Detained immigrant parents worried who will pick their children up from school.… Continue reading

Seattle judge considers reversing Trump’s EV charger funding freeze

Congress appropriated $5 billion, but the Trump administration stopped it from reaching states. Washington is leading the legal fight to access the money.

Washington’s payouts — known as tort liability — have skyrocketed from $72 million in fiscal year 2018 to more than $281 million last fiscal year. (Stock photo)
Washington state lawsuit payouts skyrocket to more than $500M in past year

Claims against the state’s Department of Children, Youth and Families are driving a spike in cases.

The Monroe Correctional Complex on Thursday, April 9, 2020. The Monroe Correctional Complex in 2020. A new law will expand Washington’s Clemency and Pardons Board to 10 members. It also requires board members to represent different backgrounds, including an incarcerated individual, a representative of a faith-based organization, a federally recognized tribe member, and a member from a crime victim organization. (Kevin Clark / The Herald)
Washington state Clemency and Pardons Board will be expanded

The goal is to cut down on wait times for people seeking to have their cases reviewed.

The Office of Superintendent of Public Instruction faces a lawsuit from a former employee alleging wrongful termination. (Photo by Bill Lucia/Washington State Standard)
Ex-Washington state worker claims she was fired over school board vote on trans athletes

Darby Kaikkonen has sued the Office of Superintendent of Public Instruction and Superintendent Chris Reykdal, alleging retaliation and wrongful termination.

Members of the California National Guard and federal law enforcement stand guard as people protest outside of the Edward R. Roybal Federal Building and Metropolitan Detention Center in Los Angeles, on Tuesday. (Philip Cheung/The New York Times)
Ferguson prepares for possibility of Trump deploying troops in Washington

The governor planned to meet with the state’s top military official Tuesday, after the president sent the National Guard and Marines to respond to Los Angeles protests.

The Washington state Capitol on April 18, 2025. (Photo by Jacquelyn Jimenez Romero/Washington State Standard)
Washington governor wants agencies to look for deeper cuts

The state’s financial turmoil hasn’t subsided. It may get worse when a new revenue forecast comes out this month.

Washington stuck mid-pack in national education ranking

The new report underscores shortfalls in reading and math proficiency. Still, the state’s top school official says data show progress recovering from the pandemic.

Washington’s Supreme Court slashes public defender caseload limits

The changes will take effect Jan. 1, but local governments get a decade to comply. For cash-strapped counties, it may not be enough time without more state aid.

Bill Lucia / Washington State Standard
State Sen. Manka Dhingra, D-Redmond, chair of the Senate Law & Justice Committee, left, asks a question during a February 2024 hearing.
New WA agency investigating police deadly force incidents sees budget cuts

The Office of Independent Investigations still plans to expand into more parts of the state this year.

Beginning on July 1, 2026, those living in Washington who qualify can begin accessing the long-term care benefit, which has a lifetime cap of $36,500, adjusted over time for inflation. Eligible beneficiaries living out of state can tap into benefits starting July 1, 2030. (Washington State Department of Social & Health Services)
Washington’s long-term care program nears liftoff

It’s been criticized, revised and survived a ballot box challenge. Now, the first-in-nation benefit is on track for a 2026 rollout.

Support local journalism

If you value local news, make a gift now to support the trusted journalism you get in The Daily Herald. Donations processed in this system are not tax deductible.