Wildfire Smoke and High Heat Have Something in Common. Guess What.

On Wednesday afternoon, President Biden was set to deliver a speech in Chicago, which was shrouded in a soupy haze from the Canadian wildfires.

“This is part of a growing pattern of extreme weather events that we’re seeing as a result of climate change,” said Olivia Dalton, the deputy White House press secretary, “and why the president has taken such ambitious, aggressive action to tackle that threat.”

Canada’s prime minister, Justin Trudeau, has also blamed human-driven warming for increases in wildfire spread and intensity. “Year after year, with climate change, we’re seeing more and more intense wildfires — and they’re starting to happen in places where they don’t normally,” he wrote on Twitter this month, shortly before cough-inducing smoke from Canada began smothering a large section of the northeastern United States.

That encounter with smoke and haze is what first drew many Americans’ attention to the fires across their northern border. But parts of Canada have continued to grapple with burning forests even if, for a time, less of their smoke was blowing in Americans’ direction. Nearly half of the 480 fires that were raging across Canada on Wednesday afternoon were classified as uncontrolled, according to the Canadian Interagency Forest Fire Center.

Higher air temperatures add to the drying out of dead leaves, branches and other flammable matter that feeds forest fires, said Jeff Wen, a doctoral candidate in earth-system science at Stanford University who studies the societal effects of wildfire smoke. “Those drier surface fuels, once ignited, burn more intensely and more severely, really damaging ecosystems,” he said.

Already this year, carbon emissions from fires in Canada have surpassed those that fires in the country have produced in any of the past 20 years, according to the European Union’s Copernicus Atmosphere Monitoring Service. The smoke is not just drifting into the United States. It has also been making its way across the Atlantic, reaching southern Europe and the British Isles before curling toward the north and east, the monitoring service said.

Michael D. Shear contributed reporting.