As the severity of wildfires becomes a growing threat to the planet’s delicate ecosystems, so too is evidence mounting of the serious risk they pose to human health.
From increased respiratory illnesses to morbidity, from adverse effects during pregnancy to the mental toll exacted in the aftermath of wildfire destruction, the blazes that have become an increasingly visceral sign of a warming planet are exacting a painful blow. “There is no safe level of exposure to wildfire smoke: the more exposure we get, the worse a range of health outcomes,” Marshall Burke, an associate professor in the Stanford Doerr School of Sustainability, said earlier this year, in the midst of one of the worst wildfire seasons Los Angeles has seen.
Wildland wildfires are gobbling up about 26% less landmass than they did two decades ago, according to research led by the United Nations University Institute for Water, Environment and Health and published by Science magazine. But the number of people exposed to fires has shot up some 40%, in part because people are living closer to areas now prone to igniting.
Wildfire smoke contributes to the deaths of about 40,000 people a year in the United States alone, a study published this year in Nature found, and that number is forecasted to rise to 70,000 people by 2050. A similar study published by the U.S. National Bureau of Economic Research in 2024 found that wildfire smoke contributes to about 16,000 deaths in the United States, and that number could climb to close to 30,000 deaths by the middle of the century.
“There is consistent and significant evidence of an association between wildfire smoke exposure and an increased risk of emergency room visits, hospital admissions, physician visits, or medication dispensations for respiratory conditions.
– Health Canada
“This really points to the urgency of the problem,” Minghao Qiu, the lead author of the report, told NPR. “Based on our results, this should be one of the policy priorities, or the climate policy priority, of the U.S., to figure out how to reduce this number.”
Another study predicted that wildfire smoke will kill 1.4 million people every year by the end of the century. And while headlines are often focused on North American or European blazes, it’s in Africa where the greatest risk is playing out. The UN University study found that 85% of global exposure to fire was in Africa.
Half a pack a day
Wildfires are a major source of pollution. In fact, they are 10 times as toxic as air pollution from the burning of fossil fuels, a recent Stanford University study found. Smoke from wildfires can affect air quality in the immediate vicinity and stretch out over great distances. As flames gobbled up forests in Northern Ontario and Alberta this past June, Toronto briefly recorded the worst air quality reading in the world, while parts of the United States were covered by a smoky haze. In Detroit, for example, air quality readings during the wildfire summer were akin to smoking a quarter or half a pack of cigarettes a day, according to one pulmonologist.
“There is consistent and significant evidence of an association between wildfire smoke exposure and an increased risk of emergency room visits, hospital admissions, physician visits, or medication dispensations for respiratory conditions,” according to a study of available research conducted by Health Canada in 2024. There is “significant” evidence, for example, linking asthma to wildfire smoke exposure. Women, children and seniors faced increased risk of respiratory morbidity, the study noted.
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A more nascent area of research is the impact that wildfires have on reproductive development. Researchers note that while there is limited comparative information, the most consistent evidence is for low birth weight and preterm birth as a result of wildfire smoke. The timing of exposure to wildfires also matters – with evidence pointing to the second and third trimesters as being the most delicate, and the severity of wildfires and proximity also influencing adverse birth effects. It’s not just about exposure to wildfire smoke; the mere occurrence of wildfires may also have an impact. “This is an important consideration, as increased maternal stress leading to the adverse birth outcomes could result from both wildfire smoke exposure and occurrence,” a 2024 Health Canada report warned.
Likewise, both exposure and occurrence may be taking a toll on mental health. A number of studies have found increased rates of post-traumatic stress disorder, anxiety and depression in both children and adults, which is in line with the climate grief that many people express in an age of seemingly constant environmental crises. The impacts of a wildfire may stretch on for months, or even years. However, it’s not clear that wildfire smoke specifically is linked to adverse mental health effects, “given the difficulties in differentiating the impacts attributable to smoke from those due to trauma associated with the wildfire occurrence (for example, potential loss of property or livelihood, physical threat, evacuation).”
For Qiu, the Stanford researcher, the importance of adaptation is ever more glaring in our learning-to-live-with-wildfire future: “We need to explore what types of adaptation strategies are most useful.” He points to improving access to air purification at home and creating networks of clean-air centres to help people avoid exposure during smoke days.
Natalie Alcoba is a Buenos Aires–based journalist and senior editor at Corporate Knights.
