Wildfire has long been a part of life for many Americans. But recently, as wildfires have become larger, more destructive and longer-lasting, a new risk has come into focus for millions across the country: wildfire smoke. People in the East, Midwest, and South have been forced to deal with smoke in recent years — many for the first time.
Now, a new study quantifies the health impacts of all that smoke. The analysis, published this week in Nature, found that wildfire smoke already contributes to some 40,000 deaths each year in the U.S. But as climate change makes fire-prone parts of North America hotter and drier, fire activity and by extension wildfire smoke could increase significantly, leading to many more Americans being exposed to dangerous, and potentially fatal, levels of smoke.
"The numbers are quite striking," says Minghao Qiu, a climate and public health scientist at Stony Brook University and the lead author of the study. By the middle of the century, smoke levels could be double or triple the average wildfire smoke concentrations experienced across the country today, he says.
2020 was one of the smokiest years in recent memory, he says, driven by a record-breaking Western wildfire season that burned some 10 million acres. Within a few decades, that amount of smoke could become the norm. Limiting future climate change could curtail some of the impacts, the study found, but more smoke is almost certainly a future reality.
Yiqun Ma, an epidemiologist at the University of California, San Diego, was not involved in the new research but led a similar study last year. She says the new results suggest Americans are going to need to think of ways to live with a smokier future. "Adaptation becomes an important topic," she says. "We need to explore what types of adaptation strategies are most useful," like helping people filter their air at home or developing a network of clean air centers that become hubs during periods of smoke.
The climate-smoke-health connection
The analysis in Nature linked three different computer models, all trained with real-world data. The first model looks at the link between Earth's changing climate and wildfire activity across North America. When temperatures are higher, explains atmospheric scientist Loretta Mickley of Harvard University, the atmosphere is thirstier: it sucks more moisture out of any available source, from lakes to soil to vegetation. Mickley was not involved in the study.
Drier vegetation, in turn, is more likely to burn, and burn in ways that can exacerbate wildfires. The model Qiu and his colleagues used in the analysis aligns with previous research, finding that a hotter planet leads to more fires—and therefore more smoke.
Then, they used a previously-developed model that looks at how smoke actually travels across the country — where it lofts high into the atmosphere, less likely to impact on-the-ground pollution, and where it comes into contact with communities.
The next step was to compare the smoke exposure each U.S. county experienced between 2006 and 2019. The team could see how that exposure changed over time — and how the death rate changed alongside the shifting smoke burden.
The results were clear. When smoke exposure was higher, more people died — and the impacts lingered, with the death rate remaining elevated for as many as three years beyond the smoke.
"We don't see smoke-related written on the death certificate," says Marshall Burke, a climate expert at Stanford University, another author of the paper. "We see heart attacks or COPD or some other complication from chronic disease. But what we know from decades of research, and what we find again in this study, is that breathing dirty air just exacerbates a range of things that make us sick."
Wildfire smoke can wreak havoc on the human body. The tiniest particles can even penetrate the bloodstream, where they drive inflammation that can last long after the smoke has disappeared, or cross the blood-brain barrier and embed into the brain. The impacts, researchers have found, can worsen health problems like heart disease and brain disease and can even contribute to premature death.
"Smoke particles tend to be more toxic than your average urban pollution," Mickley says — and because it often arrives in thick clouds, it can be even more dangerous.
The future is smokier
The researchers figured out that smoke already affects tens of thousands of people in an average year. But the future, their models show, could be even smokier.
By the middle of the century, wildfire activity is likely to increase across the country, particularly in the western U.S., as well as in Canada and Mexico — increases anywhere in North America can influence smoke exposure within the U.S.
Annual smoke exposure, in turn, could hit levels seen in what we currently think of as bad smoke years, like 2020.
Even with aggressive climate action that drastically decreases fossil fuel burning, the primary driver of global warming, smoke levels are likely to increase substantially, doubling by the middle of the century. With less effective climate action, the levels could triple. Wildfire smoke deaths, by extension, could rise from an estimated 40,000 today to some 70,000 people a year in the U.S.
Crystal McClure, a wildfire and smoke expert at the independent research group Sonoma Technologies, says the findings could even underestimate the potential health consequences. Fires that burn into urban areas often produce smoke that contains more toxins, heavy metals, and other dangerous byproducts; the study didn't explicitly include urban burns.
Overall, Burke says, the analysis confirms that climate change will continue to take a toll on Americans, costing tens of thousands of lives a year. Converted to economic losses, the health toll from climate-worsened wildfire smoke alone will exceed the economic damages the U.S. government currently considers attributable to climate change, from infrastructure losses to lost work hours, according to the analysis.
"This [finding] basically doubles our best known quantitative evidence of the impacts of a change in climate on the U.S. population," Burke says.
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