Pacific Northwest heatwave virtually impossible without human-driven climate change, finds study

People turn to extreme measures to keep cool in an extreme heatwave. (Getty Images)

The historic heat wave that struck the Pacific Northwest and killed hundreds of people would have been “virtually impossible without human-caused climate change,” an international team of climate researchers said in a new report.

The World Weather Attribution’s analysis, published July 8, 2021, Wednesday, found that the record-setting heat that triggered wildfires and was linked to hundreds of deaths was a one-in-a-1,000-year event that “would have been at least 150 times rarer without human-induced climate change.” The death toll in Oregon, U.S. alone has topped 100, while British Columbia, Canada, saw hundreds more deaths than usual. It will take months to calculate a full death toll, but scientists say these numbers will rise. Hospitals also saw jumps in the number of heat-related visits and emergency service calls.

An international team 27 scientists from the U.S., Canada, the U.K., the Netherlands, France, Germany and Switzerland spent just over a week using 21 climate models to work out how much climate change influenced the heat in areas around the cities of Seattle, Washington; Portland, Oregon; and Vancouver in Canada — covering a total population of more than 9 million.

The study said that before the industrial era, the region’s late June triple-digit heat was the type that would not have happened in human civilization. And even in today’s warming world, it said, the heat was a once-in-a-millennium event.

But that once-in-a-millennium event would likely occur every five to 10 years once the world warms another 1.4 degrees (0.8 degrees Celsius), said the study from World Weather Attribution (WWA), an international scientific collective that published the study. That much warming could be 40 or 50 years away if carbon pollution continues at its current pace, one study author said.

“There is a clear human fingerprint on this particular extreme heatwave in the Pacific Northwest, and in general on extreme heatwaves everywhere in the modern era we’re living though,” said Daniel Swain, a U.C.L.A. climate scientist who was not involved in the study, to Reuters.

Multiple cities in Oregon, Washington and the western provinces of Canada recorded temperatures “far above 104ºF,” noted the report.

These included Lytton in British Columbia setting Canada’s all-time high temperature record of 121°F on June 29. One day later, a massive wildfire swept through the village.

Maximum temperatures in several areas were up to 9 degrees higher than previous records — “by far the largest jump in the records,” noted Friederike Otto, a climate scientist at the University of Oxford in England, and study senior author to the New York Times. “We have seen quite big increases, but never that big.” “Without climate change this event would not have happened,” said Friederike Otto.

“People need to realize that heat waves are killers, and they are by far the deadliest extreme event,” said Friederike Otto, also co-leader of the WWA, an international scientific collective that published the study.

“Heatwaves are really changing so much more and so much faster than all other extreme events,” Otto said. “Heat preparation and preventing death during heatwaves need to be a No. 1 priority for every city authority.”

Although their study has yet to be peer-reviewed, the scientists used published peer-reviewed methods to conduct their analysis.

The scientists used a well-established and credible method to search for climate change’s role in extreme weather, according to the National Academy of Sciences. They logged observations of what happened and fed them into 21 computer models and ran numerous simulations. They then simulated a world without greenhouse gases from the burning of coal, oil and natural gas. The difference between the two scenarios is the climate change portion.

This heatwave was about 2C (35.6ºF) hotter than it would have been if it had occurred at the beginning of the industrial revolution in the 19th century “when global mean temperatures were 1.2°C [34.1ºF] cooler than today,” the study noted.

“Looking into the future, in a world with 2°C of global warming (0.8°C warmer than today which at current emission levels would be reached as early as the 2040s), this event would have been another degree hotter,” said the study. “An event like this — currently estimated to occur only once every 1,000 years, would occur roughly every 5 to 10 years in that future world with 2°C of global warming.”

This type of extreme heat “would go from essentially virtually impossible to relatively commonplace,” said study co-author Gabriel Vecchi, a Princeton University climate scientist. “That is 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 is telling us climate change is killing people,” said Ebi, who endured the blistering heat in Seattle. She said it will be many months before a death toll can be calculated from June’s blast of heat but it’s likely to be hundreds or thousands. “Heat is the No. 1 weather-related killer of Americans.”

What made the Northwest heatwave so remarkable is how much hotter it was than old records and what climate models had predicted. Scientists say this hints that some kind of larger climate shift could be in play — and in places that they didn’t expect.

“Everybody is really worried about the implications of this event,” said study co-author Geert Jan van Oldenborgh, a Dutch climate scientist. “This is something that nobody saw coming that nobody thought possible. And we feel that we do not understand heatwaves as well as we thought we did. The big question for many people is: Could this also happen in a lot of places?”

The WWA team does these quick analyses, which later get published in peer-reviewed journals. In the past, they have found similar large climate change effects in many heatwaves, including ones in Europe and Siberia. But sometimes the team finds climate change was not a factor, as they did in a Brazilian drought and a heat wave in India.

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

That’s because climate models used in the simulations usually underestimate how climate change alters the jet stream that parks “heat domes” over regions and causes some heat waves, said Michael Mann, a climate scientist at Pennsylvania State University.

The models also underestimate how dry soil worsens heat because there is less water to evaporate, which feeds a vicious cycle of drought, said Daniel Swain, a climate scientist at UCLA and the Nature Conservancy.

“There is a clear human fingerprint on this particular extreme heatwave in the Pacific Northwest, and in general on extreme heat waves everywhere in the modern era we are living though,” said Daniel Swain, who was not involved in the new study.

“This event was shocking to everybody who experienced it in the Pacific Northwest. Rightfully so, because there was just nothing even close to it in the modern historical record,” Swain said. “And yet it might be something that just becomes a relatively common event.”

The study hit home for University of Victoria climate scientist Andrew Weaver, who was not part of the research team.

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

“But you ain’t seen nothing yet,” he added. “It is going to get a lot worse.”

The heatwave gripped parts of the U.S. and Canada for days at the end of June, smashing records in dozens of cities. Power lines melted in the heat. Roads buckled. Canada thrice broke its national temperature record, peaking on June 29 at 121 Fahrenheit (49.6 Celsius) – a full 8 degrees Fahrenheit (4.6 degrees Celsius) higher than the previous record set in 1937.

Another heatwave is expected to hit parts of Canada and the United States later this week.

The new research attributing the heatwave to climate change is not entirely surprising. Worldwide, climate change has made heatwaves more common, more severe and longer lasting.

The June heatwave was far beyond the norm for the Pacific Northwest. For that, the authors suggested two possible explanations: Either many factors came together to produce a very rare event that was worsened by climate change, or climate change has altered the atmospheric conditions so that this type of heatwave is now more common than previously understood.

Either way, industry-driven climate change played a key, and considerable, role, according to the study.

“Most types of extreme events have been getting more frequent,” said Philip Mote, a climate scientist at Oregon State University not involved in the study. Or in the case of the Pacific Northwest heatwave, he said, extreme events were sometimes becoming “things that were almost unimaginable.”

The temperature spike was caused by what scientists call a “heat dome”, or a mass of high-pressure air parked over the region. Like a lid on a pot, the dome trapped hot air beneath it.

While the weather was unusual in its timing – record-breaking temperatures are rare so early in the summer season – last month proved to be the warmest June on record for North America, and the fourth warmest globally, scientists at the EU’s Copernicus Climate Change Service reported Wednesday.

In recent years, scientific advances have allowed researchers to link specific extreme weather events to climate crisis.


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