Scientists have reacted with incredulity after Donald Trump accused Canada of “poisoning” the US’s air with smoke billowing from a slew of forest fires and threatened sanctions upon the country’s northern neighbor. The US president has said that he raised the issue of smoke wafting into the US from nearly 1,000 Canadian wildfires with Mark Carney, the country’s prime minister, at the weekend’s World Cup final. “I told him, you got to stop these fires from coming in and poisoning our air,” Trump said.

“If we can help them, we’ll help them. But maybe they should pay us some damages or something, or we should do some tariffs.” Trump, who has previously advocated the “raking” and “cleaning” of forests to prevent major conflagrations, this week announced 50% tariffs upon Canada, a long-term US ally that he has previously threatened with annexation. The US is being “unnecessarily invaded by filthy, polluted and unhealthy air”, Trump claimed last week.

With palls of wildfire smoke causing unhealthy, hazy skies in cities including New York, Washington DC, Detroit and Toronto in recent weeks, some Republicans in Congress have issued further threats against Canada. Bernie Moreno, a Republican senator from Ohio, said he will introduce legislation to sanction Canada for the “atrocity” of not managing its forests properly. Such threats have been met with shock in Canada, where thousands of people have been evacuated from fires that have badly burned remote towns.

More than 8.1m acres (3.3m hectares) have been consumed by fires across Canada’s vast, mostly unpopulated boreal forests, a steep increase on the long-term average. Such fierce wildfires are a symptom of the climate crisis rather than a lack of management, experts warn, with the current blazes worsened by the recent severe heat dome that expanded from the US into Canada. The world is rapidly heating up due to the burning of fossil fuels, a process that Trump has actively sought to accelerate.

“This is like crashing into the car in front of you because you were speeding and tailgating, and then demanding they pay for the damage to your headlights,” said Michael Mann, a climate scientist at the University of Pennsylvania, of Trump’s comments. “It’s victim-blaming by the assailant. “The policies of Trump and the GOP are worsening the problem by doubling down in fossil fuel production and doing their best to obstruct the clean energy transition while the rest of the world moves on,” Mann added.

While Trump has falsely dismissed established climate science as “crap”, there is robust evidence linking prolonged hot, dry weather with fire-prone conditions. Elevated temperatures caused by the climate crisis more than doubled the likelihood of severe fire conditions when Canada was last engulfed by major wildfires in 2023, a previous analysis found. “The main cause of worsening fires in Canada is not mismanagement – most Canadian forests are remote and haven’t been managed at all, unlike the US – but instead a warming climate that has made large and extreme wildfires more common,” said Marshall Burke, an environmental policy expert at Stanford University.