"The bottom line is that the amount of climate change we get is really determined by us, and by the people we elect to either mitigate emissions of carbon dioxide and other greenhouse gases or not," he said. "And the less we do, the worse things get."
The Columbia researchers also found that several factors converged to help create the blistering heat dome, including anomalously dry soils and disruptions to the jet stream.
In California and other parts of the Western United States, increasing heat, drought and aridification are contributing to long-term drying of soils, which means there's less water to be evaporated into the air, Bartusek explained.
"And if there is less ability for evaporation to come out of the ground, there is a greater heating effect — where the air that's just above the surface will be heated more effectively," he said. He added that in some areas it's likely there was "this feedback process going on where the land surface helped amplify some of the highest temperatures."
The jet stream — the fast-flowing air currents in the upper level of the atmosphere that guide weather systems from west to east — also played a role in the heat wave, according to the study. Before and during the event, the jet stream "buckled" into a wave pattern and slowed down, essentially locking the weather system in place and allowing the dome of heat to build up over the region.
The researchers noted that the effect of climate change on the jet stream is still being debated, although some scientists believe such wave patterns are becoming more frequent and extreme due to human activity. Wehner said the question is "one of the most interesting problems in climate science right now."
"It definitely remains a possibility that we would see more of these kinds of unusual flows with global warming," he said.
Kai Kornhuber, an adjunct associate research scientist at the Lamont-Doherty Earth Observatory and another of the Columbia study's authors, said the findings highlight how deviations among soil moisture levels, the jet stream and other factors can drive temperatures even beyond their usual magnitudes.
"Sometimes these factors just align and you get those conditions that cause a perfect storm," he said. "What is important to mention here, though, is that each of those drivers do exhibit increasing trends that are associated with climate change ... These types of coincidences might just occur with a higher likelihood in the future, just because these common drivers are all linked to climate trends."
As for how likely it is that such heat waves will reach that yearly 10% probability by 2050, much depends on which emissions pathway society ends up taking. But "given the accelerated trends in extreme weather events globally, there are reasons to believe that these estimates might even be a bit conservative," Kornhuber said.
He and the other researchers noted that while some of the studies' numbers and predictions may differ, their key messages are very similar — that the extreme heat wave was essentially impossible at pre-industrial emission levels.
"What is important in this aspect is these methods all agree that climate change plays a major role in every heat wave that we observe nowadays," Kornhuber said.
Though the findings are dire, the researchers said they could help inform future modeling of such events and help people to better prepare. Many parts of the Pacific Northwest were unequipped for such extreme heat, including homes without air conditioning and infrastructure systems unable to handle such strain. Wehner said improved adaptation efforts and contingency plans will help, but that ultimately, such events "are going to get worse because there's a lot of climate change that's baked into the system."
"The more we can reduce our emissions — eventually getting down to none, to zero — and the sooner we can do that, the better in terms of avoiding even worse tragedies," he said.
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