The brutal heat wave that killed hundreds of people last week in the Pacific Northwest and Canada would have been "virtually impossible" without climate change, a study released on Wednesday said, offering the latest evidence that global warming is making extreme heat more common and more dangerous.
In a preliminary analysis, called a rapid attribution study, an international team of 27 scientists examined the links between human-induced climate change and the heat wave, finding that the blistering temperatures were made at least 150 times more likely to occur because of climate change.
“Basically without climate change, this event would not have happened,” Friederike Otto, one of the study authors and a climate scientist at the University of Oxford, told reporters on Wednesday.
And what this and other climate attribution studies are making clear is that “heat waves are increasing in likelihood by orders of magnitude more than any other type of extreme event,” Otto said. “Heat waves [are] how climate change kills us today.”
Earlier this week, Oregon’s Multnomah County, home to Portland, declared the recent heat wave “a mass casualty event,” after health officials identified 67 possible deaths linked to heat stress, or hyperthermia. Upward of 107 people total are suspected to have died due to heat across Oregon, on top of about 57 possible deaths in Washington state and more than 500 deaths in Canada. Local officials have warned that a full accounting of the heat wave’s death toll could take months.
The heat drove more than 2,000 people to the hospital and urgent care clinics. It cracked open pavement, caused businesses to shut down, and resulted in mass die-offs of clams, mussels, starfish, and other sea creatures along the Washington and British Columbia coastlines.
The heat wave set new high-temperature records across Canada and the Pacific Northwest — 116 degrees Fahrenheit around Portland, 108 degrees near Seattle, and 121 degrees in Canada’s small town of Lytton — stunning even climate scientists. The staggering toll of the disaster was due in part to the fact that the unprecedented temperatures lingered for several days in a part of the world where many people don’t have air conditioning.
The research team leading the rapid attribution study focused on the impacted areas with the highest populations, including Portland, Seattle, and Vancouver.
“We immediately ran into a problem,” said Geert Jan van Oldenborgh of the Royal Netherlands Meteorological Institute. Because the observed temperatures were far above what scientists had ever seen before, or even thought possible, the models initially couldn’t replicate them.
Ultimately, they adjusted the models to account for such dramatic events, estimating that the peak of the heat wave was a 1-in-1,000-year event made at least 150 times more likely because of climate change. Climate change also made the heat wave hotter — an estimated 3.6 degrees higher than if it had occurred before the Industrial Revolution. And they concluded that such events will continue to get hotter and become more frequent if climate change continues on its current path.
The scientists stressed that they still did not understand exactly how such high temperatures could be physically created, making it difficult to know how likely another similar heat wave could be.
“Everyone is just worried about the implications of this event,” said van Oldenborgh. “This is something that nobody saw coming, that nobody thought possible. And we feel we do not understand heat waves as well as we thought we did. And the big question for many people is, could this happen in other places?”
Van Oldenborgh and his colleagues said they will keep studying the issue until they get an answer. “At the moment, we just don’t know,” he said. “We need to continue with this analysis.”