Scientists say climate change has made Canada’s extreme fire weather twice as likely, challenging claims that forest mismanagement drove the crisis.
Human-caused climate change doubled the likelihood of the weather conditions that fueled Canada’s massive summer wildfires, according to a study released on Thursday, as U.S. President Donald Trump continued to blame Canadian forest management for the blazes and the smoke that spread into the United States.
Fire and climate scientists said Trump was directing blame at the wrong target, arguing that the United States’ long history of greenhouse gas emissions from burning coal, oil and gas has played a far greater role in creating the conditions that intensified the fires.
The study by World Weather Attribution, an international group of scientists that examines the influence of climate change on extreme weather events, found that the fire weather conditions in the Northwest Territories and northwestern Ontario were unusual but not exceptionally rare. However, global warming made those conditions twice as likely to occur.
The findings are comparable to those the group reported for summer wildfires in France, though the climate signal was not as strong as in Spain, where researchers said climate change made wildfire conditions 20 times more likely.
The rapid study, which has not yet undergone peer review, examined the weather factors associated with major wildfires using Canada’s fire weather index. It assessed heat, rainfall deficits, humidity and wind, comparing current conditions with a world that had not experienced the 2.5 degrees (1.4 degrees Celsius) of warming since the industrial age and the widespread burning of fossil fuels.
The researchers concluded that the weeklong weather conditions preceding the Ontario fires are now expected about once every six years.
“In a pre-industrial climate this would have been much less likely to occur, maybe once in a lifespan. So climate change has made those events more likely,” said Jonathan Boucher, a fire scientist at Canada’s Forest Service and a co-author of the study.
Scientists not involved in the research said its conclusions were consistent with growing evidence that hotter and drier conditions are making wildfires more frequent and more intense.
“Mother Nature’s been burning. Now she’s on amphetamines and she burns more and more,” said Mike Flannigan, a fire scientist at Thompson Rivers University in Canada who was not involved in the study.
Hazardous smoke spread across both Canada and the United States, affecting major cities including New York.
By continuing to burn more fossil fuels, “we’re putting nails in our coffins,” Flannigan said.
In the larger and more remote fires in the Northwest Territories, where more than 5,000 square miles (12,950 square kilometers) burned, lightning clearly ignited the fires. However, it was the climate conditions that allowed them to intensify rapidly and spread beyond control, according to Boucher and Theodore Keeping, the report’s lead author and a climate scientist at Imperial College London.
Although people are responsible for about half of Canada’s wildfires, either accidentally or intentionally, lightning-caused fires account for more than 90% of the country’s total burned area, Flannigan said.
“What we’re facing here is more of a climate related problem than a forest management problem,” Boucher said.
Trump has rejected that assessment.
“A lot of damage has been done. They’re not managing their forests properly,” Trump said on July 21. “And the wind has a tendency to blow right over New York City, right over, you saw Detroit, they had to close the whole place. Michigan was really affected. They had to close businesses for four days. It’s very serious what they’re doing, and they don’t seem to be able to do anything about it. If they managed their forests, they wouldn’t have the fires.”
Asked on Sunday about possible measures against Canada, Trump told reporters aboard Air Force One that he had decided on a punishment, adding, “you’ll find out about it soon.”
Canadian climate and fire experts said the president was overlooking the underlying causes of the fires.
“Smoke does not carry a passport, but carbon pollution does have a history. That history shows that the United States contributed more than any other country,” said Andrew Weaver, a climate scientist at the University of Victoria. “President Trump is pointing at the smoke while ignoring America’s fingerprints on the climate conditions behind it.”
Friederike Otto, an Imperial College London climate scientist and co-author of the study, said, “if you care about anyone but the super rich, you have to stop burning fossil fuels because the impacts are here and they’re now and have huge consequences.”
Canada has warmed 65% more than the United States in recent decades. Over the past 30 years, the area burned annually by wildfires has increased by about 50% in Canada, while the corresponding area in the United States has more than doubled.
Boucher and Flannigan said another challenge overlooked by Trump is that much of Canada’s forest is located in remote northern regions dominated by fast-burning spruce and pine, making suppression efforts especially difficult.
“In Canada, when things are extreme, you have about a 30-minute window to put that fire out,” Flannigan said. “If you don’t get there in 30 minutes, you’re out of luck. And many of the fires that start in Canada are northern remote areas that are more than 30 minutes away from an airport. So even with perfect detection systems, we would get there too late and these fires are going to burn.”
