Deadly Pacific Northwest Heatwave: ‘Virtually Impossible’ Without Man-Made Warming

The first scientific judgments on the deadly, record-shattering heat wave that blasted the Pacific Northwest at the end of June are starting to roll in. One rapid attribution analysis, conducted by scientists at World Weather Attribution, found that a heatwave this severe “was virtually impossible without human-caused climate change.”

The “heat dome” event — created by an extreme high-pressure system over British Columbia, Washington state and Oregon that blocked typical, cooling ocean breezes — transformed an area famous for its temperate climate into a desert-like furnace with temperatures soaring well into the triple digits. This analysis found that the temperatures observed in the Pacific Northwest (Portland hit a record shattering 116 degrees) “were so extreme that they lie far outside the range of historically observed temperatures,” and described that existing modeling pegs it at “about a 1-in-1,000 year event in today’s climate.”

Our current climate is already influenced by global warming, with about 1.2°C now baked into the world’s climate system. The scientists said that a heat event of this magnitude is 150 times more likely today than it would have been at the beginning of the industrial revolution — when it would have been a 1-in-150,000 year event. Global warming is not uniform, is more extreme at northern latitudes, and amplifies the extremes of heat events. “This heatwave was about 2°C hotter than it would have been if it had occurred at the beginning of the industrial revolution,” the scientists write.

The science highlights the need for urgent action on climate change. Unchecked warming could increase global temperature rise by another 0.8°C within decades. In that climate, a the Pacific Northwest could expect a return of June’s unfathomable heat “roughly every 5 to 10 years.”

We underestimate just how big a difference global warming can make to the likelihoods of extremes.

200 years ago odds of an event like the Pacific NW heatwave would have been 1 in 150,000 years

With 1.2C global warming it was a 1 in 1,000 years

At 2C it would be 1 in 10 years

— Zeke Hausfather (@hausfath) July 8, 2021

Rapid attribution analysis uses peer-reviewed methods to try to quickly tease out the influence of climate change in extreme weather events. Such an analysis does not go through all the hoops that would be required to gain publication in a scientific journal, but is intended to help the public understand the influence of global warming in near real-time. This study is a collaboration of climate scientists from the United States, Canada, and numerous countries across Europe.

The days of extreme heat in the Pacific Northwest, where many residents lack air conditioning, were deadly. In Oregon alone, more than 100 deaths have been blamed on the heat, with authorities now calling it a “mass casualty event.” The World Weather Attribution authors warn that this early count is “almost certainly an underestimate,” adding that the the full death toll likely won’t be known for “several months.” They underscore that “heatwaves are one of the deadliest natural hazards” and that global warming is pushing us into “uncharted territory that has significant consequences for health, well-being, and livelihoods.”

The study notes that present climate models suggest the heat wave was “the statistical equivalent of really bad luck, albeit aggravated by climate change.” But the analysis also raises a far more troubling hypothesis: That man-made warming may be creating “nonlinear interactions in the climate” that “substantially increased the probability of such extreme heat.”

The authors explain: “Based on this first rapid analysis, we cannot say whether this was a so-called ‘freak’ event… or whether our changing climate altered conditions conducive to heatwaves in the Pacific Northwest.” If that were the case, they write, it means “that ‘bad luck’ played a smaller role, and this type of event would be more frequent in our current climate.”

In either case the authors conclude that unchecked climate change will turn our luck from bad to worse when it comes to such a rare event: “As warming continues,” they write, “it will become a lot less rare.”