North-West heatwave impossible without climate change


The deadly heat wave that ravaged the Pacific Northwest and western Canada was virtually impossible without man-made climate change that added a few more degrees to record temperatures, a quick new scientific analysis has revealed.

An international team of 27 scientists has calculated that climate change increases the chances of extreme heat occurring at least 150 times, but probably much more.

The study, not yet peer-reviewed, said that before the industrial age, the region’s triple-digit heat at the end of June was of the type that would not have occurred in human civilization. And even in today’s warming world, he said, the heat was a unique event in a millennium.

But this one-time event in a millennium would likely occur every five to ten years once the world warms 1.4 degrees (0.8 degrees Celsius), according to Wednesday’s World Weather Attribution study. That warming could be 40 or 50 years from now if carbon pollution continues at its current rate, one study author said.

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This type of extreme heat “would go from practically impossible to relatively mundane,” said study co-author Gabriel Vecchi, a climatologist at Princeton University. “It’s a huge change.”

The study also found that in the Pacific Northwest and Canada, climate change was responsible for about 3.6 degrees (2 degrees Celsius) of the heat shock. Those few degrees make a big difference in human health, said study co-author Kristie Ebi, a professor at the Center for Health and the Global Environment at the University of Washington.

“This study tells us that climate change is killing people,” said Ebi, who endured the scorching heat in Seattle. She said it will be several months before a death toll can be calculated from the June heat wave, but there are likely to be hundreds or thousands. “Heat is the No. 1 killer of Americans when it comes to weather.”

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In Oregon alone, the state medical examiner reported 116 heatwave-related deaths on Wednesday.

The team of scientists used a well-established and credible method to research the role of climate change in extreme weather conditions, according to the National Academy of Sciences. They recorded observations of what happened and incorporated them into 21 computer models and performed numerous simulations. They then simulated a world without greenhouse gases from burning coal, oil and natural gas. The difference between the two scenarios is the share of climate change.

“Without climate change, this event would not have happened,” said lead study author Friederike Otto, a climate scientist at the University of Oxford.

What made the Northwest heat wave so remarkable was how hotter it was than old records and what climate models predicted. Scientists say this hints that some sort of bigger climate change could be at play – and in places they didn’t expect.

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“Everyone is really worried about the implications of this event,” said study co-author Geert Jan van Oldenborgh, a Dutch climatologist. “This is something that no one saw coming, that no one thought possible. And we think we don’t understand heat waves as well as we thought. The big question for a lot of people is, this might- does it also occur in many places? “

The World Weather Attribution team performs these quick scans, which are then published in peer-reviewed journals. In the past, they have seen similar effects of climate change in many heat waves, especially in Europe and Siberia. But sometimes the team finds that climate change was not a factor, as it did during a drought in Brazil and a heat wave in India.

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Six outside scientists said the quick study made sense and likely underestimated the extent of climate change’s role in the heat wave.

This is because the climate models used in the simulations generally underestimate how climate change alters the jet stream that parks “heat domes” over regions and causes heat waves, Michael said. Mann, climatologist at Pennsylvania State University.

The models also underestimate how much dry soil makes heat worse because there is less water to evaporate, which fuels a vicious cycle of drought, said Daniel Swain, climatologist at UCLA and Nature Conservancy.

The study affected University of Victoria climatologist Andrew Weaver, who was not on the research team.

“Victoria, which is known for its mild climate, looked more like Death Valley last week,” Weaver said. “I’ve been to a lot of hot places around the world, and this was the worst I’ve ever been to.

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“But you haven’t seen anything yet,” he added. “It’s going to get worse.”


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Follow Seth Borenstein on Twitter at @borenbears.


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