Climate change made the record-shattering Northwest heat wave 150 times more likely

Yes, blame climate change.

Human-driven global warming fueled the heat wave that likely killed hundreds of people last week across the US Pacific Northwest and Canada.

The massive buildup of greenhouse gases in the atmosphere made the unprecedented weather event 150 times more likely, according to an analysis by World Weather Attribution. The loosely affiliated team of global scientists concluded that the extreme heat wave would have been “virtually impossible” without climate change, which has already warmed the planet by about 2.2 ˚F (1.2 ˚C).

Scientists long resisted pinning any single weather event on climate change, sticking to the general point that it would make heat waves, droughts, fires, and hurricanes increasingly frequent and severe. But more satellite data records, increased computing power, and higher-resolution climate simulations have made researchers more confident about stating, often within days, that global warming substantially raised the odds of specific disasters. (See 10 Breakthrough Technologies 2020: Climate Change Attribution.)

Last week’s extreme temperatures demolished all-time heat records in cities and towns throughout the region, knocked out power to tens of thousands of homes, and put more than 2,000 people into emergency rooms for heat-related illnesses in Washington and Oregon.

So far, officials have reported more than 100 heat-linked deaths in those states, according to assorted media outlets. In addition, there were nearly 500 “sudden and unexpected deaths” in British Columbia, some 300 more than normal during the relevant five-day period.

The most likely scenario is that higher global temperatures simply exacerbated the consequences of unusual atmospheric conditions that occurred last week, when a so-called heat dome trapped hot air over a massive stretch of the region. If so, similar events could happen once or twice a decade if temperatures rise by 3.6 ˚F (2 ˚C), the researchers found.

The more troubling, if slimmer, possibility is that greenhouse-gas emissions have pushed the climate system past some unknown and little-understood threshold, where planetary warming is now triggering sharper rises in extreme temperatures than expected. That theory will require further research to assess. But it would mean that severe heat waves will exceed the levels current climate models predict, the researchers said.

“You’re not supposed to break records by four or five degrees Celsius (seven to nine degrees Fahrenheit),” Friederike Otto, co-lead of World Weather Attribution and associate director of the Environmental Change Institute at Oxford University, said in a statement. “This is such an exceptional event that we can’t rule out the possibility that we’re experiencing heat extremes today that we only expected to come at higher levels of global warming.”

Another heat wave is expected to push temperatures back into the triple digits across parts of the Northwest in the coming days.