Increasingly ferocious wildfires in the western US are taking a devastating toll on the region’s air quality, with wildfire smoke now accounting for half of all air pollution during the worst wildfire years, according to a new study.
Scientists from Stanford University and UC San Diego have found that toxic plumes of smoke, which can blanket western states for weeks when wildfires are raging, are reversing decades of gains in cutting air pollution. While heat-related deaths have previously been predicted as the worst consequence of the climate crisis, researchers say that air pollution caused by smoke could be just as deadly.
“For a lot of people in this country wildfires are going to be the way they experience climate change,” said Marshall Burke, an associate professor of earth science at Stanford and one of the study’s authors. “The contribution of wildfires to poor air quality has roughly doubled in the last 15 years in the west.”
Air pollution from fine particles, known as PM2.5s, was already known to take four months off the lifespan of the average American. And health researchers are just beginning to understand the harrowing health consequences added by the increasing smoke exposure for broad swaths of the US population.
Wildfire seasons have become increasingly brutal in the American west, exacerbated by the climate crisis. The firestorms of 2020 were among the worst in recorded history, with 31 people killed, 10,000 buildings destroyed or damaged and more than 4m acres burned in California alone. Huge swaths of Colorado, New Mexico and Arizona were scorched as well.
After California’s residents endured a month of orange-brown air filled with dangerous tiny particles, another set of Stanford researchers tracked dramatic increases in hospitalizations for things like strokes, heart attacks and asthma.
Bibek Paudel, a postdoctoral researcher at Stanford’s asthma clinic found that hospitalizations for strokes increased by 66% in the five weeks after fires caused by lightning strikes began sending smoke around northern California last August. The number of pregnancies lost also doubled in the weeks after the fires – a startling finding that the researchers are still interpreting. Paudel also found significant increases in heart attacks and youth hospitalization for respiratory illness.
“I don’t think that people are aware of the long-term health effects of wildfire smoke,” said Mary Prunicki, the director of research for Stanford’s Sean N Parker Center for Allergy & Asthma Research.
For decades, air quality in the US has been improving due to reductions in pollution from cars and factories, mandated by the Clean Air Act. But over the last 40 years, the amount of land burned in wildfires has quadrupled, Burke’s study found.
The study, published in the Proceedings of the National Academy of Sciences, combined data from satellite images of smoke plumes with measurements obtained from air monitors on the ground, which record local air pollution, to model the total smoke exposure. The study comprised all states west of (and including) New Mexico, Colorado, Wyoming and Montana.
Smoke plumes can be detected by satellite images as they travel across the country. But it is hard to tell whether they are low enough to affect the air quality on the ground, so the study created statistical models of how pollution changed in specific locations after fire events, combining information from satellites, air monitors and data models.
“Everyone knows wildfires produce dirty air – so that’s not a surprise,” said Burke. “What we were able to do in this study is quantify how large that contribution is. And we found it’s really reversing a lot of the progress that’s been made across the country in air quality improvement.”
Surprisingly, the study found that wildfire smoke is spreading the effects of air pollution to whiter and wealthier populations. Historically, low-income communities have been hardest hit by air pollution, often because their homes are closest to freeways and factories. But smoke spreads pollutants over much broader areas. Burke said the western US, where the most wildfires occur, also tends to be whiter and wealthier than other regions of the country.
As the plumes travel around the country, the pollutants can harm even people living far from the fires, in the midwest or east.
“Wildfire smoke is a burden that is much more equally shared than other pollution,” said Burke.
However, other research has shown that low-income populations may be hit harder when smoke blankets a region, because their smaller and older homes offer them less protection.
Ironically, one of the future solutions to all this smoke may be to light more fires.
The increase in wildfires is due in part to warmer temperatures and drier conditions, but there is a growing consensus that it is also a result of the nation’s policy of suppressing fires, instead of occasionally letting land burn.
“There’s a huge amount of fuel on the ground,” said Burke. “Climate change is drying it out and making it much more flammable.”
Burke said a policy of using prescribed burns, which involve lighting carefully controlled fires to clear some of the brush, could be a major strategy for reducing wildfires and cutting dangerous smoke exposures in future years.
“The benefits might be quite large, but there are a number of key questions that need to be studied,” he said.
Otherwise, “under business as usual, years like 2020, which was off-the-charts historically, may become much more of the norm,” he said. “It’s sort of terrible to think about.”