Climate change made the massive wildfires in Canada that choked the eastern U.S. with toxic smoke earlier this summer twice as likely, a new analysis from World Weather Attribution finds. The international team of scientists, using established, peer-reviewed methods, also determined human-caused climate change made wildfire seasons of this severity seven times more likely to occur.

“The word ‘unprecedented’ doesn’t do justice to the severity of the wildfires in Canada this year,” Yan Boulanger, a research scientist at Natural Resources Canada and part of the WWA team, told The Guardian. “From a scientific perspective, the doubling of the previous burned area record is shocking. Climate change is greatly increasing the flammability of the fuel available for wildfires – this means that a single spark, regardless of its source, can rapidly turn into a blazing inferno.”

Snowcover has historically limited Canadian wildfires, but “high temperatures led to the rapid thawing and disappearance of snow during May, particularly in eastern Quebec, resulting in unusually early wildfires,” said Philippe Gachon, a researcher at the Université du Québec à Montréal. “The ongoing loss of snow in a warming climate means that wildfires will burn for many more days each year in Canada.”

Tinderbox-like conditions

“Increasing temperatures are creating tinderbox-like conditions in forests in Canada and around the world,” Friederike Otto, a climate scientist at Imperial College London, told The Guardian. “Until we stop burning fossil fuels, the number of wildfires will continue to increase, burning larger areas for longer periods of time.”

The WWA report only assessed wildfires in Canadian wildfires in May and June of this year, but the entire Canadian wildfire season has been superlative breaking — doubling the total acreage burned of the next-worst year and forcing the evacuation of more than half the population of the Northwest Territories, including numerous Indigenous towns and the entire provincial capital of Yellowknife. (The Guardian, AP, NPR, New York Times $, CNN, ABC, Deutsche Welle, Bloomberg $, Weather Channel, E&E $, Reuters, NBC, CBC, AFP via Barron’s, The Globe and Mail, Politico Pro $; Climate Signals background: Wildfires)