Wildfire smoke is responsible for tens of thousands of deaths each year and will cause more harm to U.S. residents by mid-century than any other threat caused by climate change, including extreme heat.
That's the conclusion of a new research paper that provides the most extensive modeling of the growing public health costs of wildfire smoke in the United States.
The study that was published in the journal Nature on Thursdayfound that every year, on average, smoke from forest fires causes more than 41,400 additional deaths, or more than would normally be expected without the smoke, given US demographics. This figure is more than double that previously recognized in other studies.
The study authors expect that number to rise by another 26,500 to 30,000 deaths by mid-century as human-caused climate change worsens and the risk of wildfires increases.
“Wildfire smoke poses a much greater health risk than we previously imagined,” said Marshall Burke, a professor of environmental social sciences at Stanford University and an author of the study.
When quantified in economic terms, Burke said he and his colleagues were surprised to find that the cost of smoke deaths exceeded all other monetary losses associated with climate change in previous studies, such as agricultural losses, heat deaths and energy costs.
A growing body of research shows that wildfire smoke exposure is caused by… serious health problems. Fine particles from wildfire smoke enter the lungs and can circulate in the bloodstream. Smoking may increase your risk of developing asthma, lung cancer, and other chronic lung diseases. Wildfire smoke has also been linked to premature birth and miscarriage.
The study offers a stark vision of a nation increasingly choked by tobacco smoke. Decades of work to clean up industrial air pollution in the US through the Clean Air Act are being reversed as fires in the western US and Canada send plumes of smoke into the atmosphere that then spread across the landscape.
“Smoke from wildfires is starting to turn back the clock on air pollution levels, at least in the western states and New York,” said Dr. Joel Kaufman, a professor of medicine, epidemiology and environmental health at the University of Washington who studies air pollution but did not work on the study. “It's an emerging danger, and it's one of the few things that can probably be realistically put at the root of climate change. That's the rub.”
And there's only so much that can be done: The study suggests that the death toll from wildfire smoke will increase by 64% to 73% or more by mid-century, depending on emissions levels.
“No matter what we do in mitigation, we will likely see a lot more smoke by 2050,” Burke said, adding that efforts to reduce emissions will pay off in the long run.
Kaufman said there has been “a wealth of evidence” over the past five to 10 years suggesting that wildfire smoke is at least as harmful as other forms of air pollution.
“There was an assumption that burning wood was less toxic,” Kaufman said. “These results suggest that wildfire smoke may be more toxic,” especially when the wildfire burns through buildings, cars and other human-made materials.
Kaufman noted that the fires in Los Angeles earlier this year started as a wildfire, but it was mostly people's houses and human plastic that was burningemitting “another toxic soup.” The new study doesn't differentiate between sources of future wildfire smoke.
The new research could have implications for public policy.
The Environmental Protection Agency is trying to repeal a key provision of the law known as “threat identification.” as part of a broad rollback of environmental regulations. This 2009 legal decision states that greenhouse gases such as carbon dioxide and methane heat up Earth, and that warming poses a threat to public health and welfare. It serves as the basis for the agency's greenhouse gas pollution regulations under the Clean Air Act.
The new study could be part of a “counteraction” to the measure, said Dr. John Balmes, a spokesman for the American Lung Association and a professor at the University of California, San Francisco School of Medicine.
The measure to overturn the imprisonment is going through a lengthy regulatory process that is now accepting public comments. Balmes said he cited the study in a letter opposing the EPA's changes.
“This reinforces what we've been saying about the connection between wildfires and climate change and the subsequent public health impacts,” Balmes said.
The National Academies of Sciences, Engineering and Medicine released the report on Wednesday that human-caused warming is causing harm and will continue to cause harm in the future. The evidence is “beyond scientific controversy,” said the committee that wrote the report.
The White House did not respond to requests for comment. The Environmental Protection Agency said the Trump administration is “committed to reducing the likelihood of devastating natural disasters” and will prioritize efforts such as prescribed burning, fuel treatment and debris removal to prevent them.
“EPA welcomes all public comments on the proposal to rescind the 2009 hazard opinion by September 22, 2025, and the agency looks forward to responding to a wide range of viewpoints on this issue,” the spokesperson said in an email.
In the Nature study, researchers estimated the number of additional wildfire smoke deaths each year by comparing three models: one that estimates the impact of climate change on overall fire activity, another that models expected changes in fire activity and where smoke will spread, and a third that quantifies health effects resulting from long-term smoke exposure.
The researchers used 2011-2020 as a baseline and projected future conditions under several climate scenarios. They had access to all U.S. deaths during this period, satellite and ground-based smoke travel data, global climate models, and other data sets.
The study assumes that people will take the same steps to avoid exposure to smoke as they do today.
The study has limitations – mainly, it relies on a number of models to reach national conclusions. The study does not track each individual smoke death, track a person's exposure to smoke, and then catalog the health effects.
The results of the study were published along with second study in Nature who used similar methods and looked at the problem around the world. A separate research team estimates that by the end of this century, the number of premature deaths from wildfire smoke could rise to about 1.4 million per year, about six times higher than today.
