The study, which took a little more than a week, is not yet peer-reviewed or published in a scientific journal. But it uses techniques that have been peer-reviewed before over the decade that these kinds of studies have been done. World Weather Attribution itself has completed about 30 of them since 2015.
Essentially the research uses computer simulations, 21 in all for this analysis, to compare what happens in the existing world, which has warmed about 2 degrees Fahrenheit since the rise of industry and its accompanying emissions, to a hypothetical world in which humans had never pumped any greenhouse gases into the atmosphere.
Climate scientists are certain that global warming has made heat waves worse, because the baseline temperatures from which they begin are higher than they were decades ago. Rapid attribution analysis attempts to answer two questions about a specific heat event: how much worse, and how much more likely, did climate change make it?
For the Pacific Northwest heat wave, the analysis showed that, even though rare, it was far more likely to occur in the current warmed world than in a world without warming. And if the heat wave had occurred in such a hypothetical world, it would not have been as hot, with maximum temperatures about 3.5 degrees lower.
But the extreme nature of this heat wave gave the scientists pause. Maximum temperatures in many locations were 7 to 9 degrees higher than previous records, roughly twice the increase seen in other heat waves.
“It was by far the largest jump in the records,” Dr. Otto said. “We have seen quite big increases, but never that big.”