As deadly wildfires raged in the Canadian province of Manitoba this summer, Republican lawmakers in nearby U.S. states penned letters asking that Canada be held accountable for the smoke drifting south.
Our skies are being choked by wildfire smoke we didn't start and can't control, wrote Calvin Callahan, a Republican state representative from Wisconsin, in a letter dated early August.
Callahan, along with lawmakers from Iowa, Minnesota and North Dakota, filed a formal complaint with the U.S. Environmental Protection Agency (EPA) urging an investigation into Canada's wildfire management.
Manitoba premier Wab Kinew quickly condemned the move, accusing the lawmakers of throwing a timber tantrum and playing political games.
By August, the wildfires had scorched more than two million acres in Manitoba, forced thousands to evacuate, and killed two people – a married couple who authorities said were trapped by fast-moving flames around their family home.
As September draws to a close, data shows that 2025 is on track to be Canada's second-worst wildfire season on record.
A study published in the Nature journal in September has revealed that smoke from Canada's wildfires has also had far-reaching, fatal consequences. It estimates that the 2023 wildfires - the country's worst on record by area burned - caused more than 87,500 acute and premature deaths worldwide, including 4,100 acute, smoke-related deaths in the U.S. and over 22,000 premature deaths in Europe.
Wildfire smoke contains PM2.5 - a type of air pollution - that is known to trigger inflammation in the body. It can exacerbate conditions like asthma and heart disease, and, in some cases, can damage neural connections in the brain.
These are big numbers, said Michael Brauer, a professor at the University of British Columbia who co-authored the study. He added the findings show wildfire smoke should be treated as a serious health issue, akin to breast cancer or prostate cancer.
For some American lawmakers, the blame falls squarely on Canada. Canada's failure to contain massive wildfires, Callahan wrote in August, has harmed the health and quality of life of more than 20 million Americans in the Midwest.
Climate and fire experts in both countries told the BBC that the answer is largely no. Until we as a global society deal with human-caused climate change, we're going to have this problem, said Mike Flannigan, an emergency management and fire science expert at Thompson Rivers University in British Columbia.
Metrics show Canada's wildfires, a natural part of its vast boreal forest, have worsened in recent years. Fire season now starts earlier, ends later, and burns more land on average. The 2023 fires razed 15 million hectares (37 million acres) – an area larger than England – while the 2025 blazes have so far burned 8.7 million hectares (21.5 million acres).
As of mid-September, there are still more than 500 fires burning, mostly in British Columbia and Manitoba, according to the Canadian Interagency Forest Fire Centre.
Approximately half of Canada's wildfires are sparked by lightning, while the rest stem from human activity, data from the National Forestry Database shows. Experts warn that hotter temperatures are making the land drier and more prone to ignition.
In recent months, the Trump administration has also rolled back environmental policies designed to reduce emissions, further complicating the situation.
Professor Brauer emphasized the studies highlight that the effects of climate change are not just localized but have global repercussions, underscoring the importance of addressing these issues collaboratively rather than assigning blame.
