United States President Donald Trump has accused Canada of “wilful negligence” over wildfires, blaming its forest management, threatening tariffs and floating demands for compensation. His argument is absurd.

Smoke does not carry a passport. Wildfires are burning across several countries, causing evacuations and devastating communities. In North America, smoke from fires has spread over many parts of central Canada and the U.S.

Wildfires are currently scorching vast areas in Oregon and the Pacific Northwest. France and Spain have evacuated hundreds of thousands of residents as wildfires close in on Bordeaux, France, and grow around Madrid, Spain. Despite Trump’s claims, Canada cannot log, rake or prescribe-burn its way out of a planetary problem.

Wildfires require ignition, combustible fuel and weather that permits rapid spread. Climate change does not usually strike the match — people and lightning do that, with lightning responsible for most of the area burned in Canada. But warming weather increasingly determines whether a spark dies or becomes a catastrophe. Hotter air, earlier snowmelt and longer summers mean a drier landscape and more severe fire seasons.

In 2004, colleagues and I demonstrated that human-caused climate change had already left a detectable fingerprint on the area burned by Canadian forest fires. A 2024 study found that human influence has made fire seasons like Canada’s record 2023 season more........

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