Silent Calamity The Health Impacts of Wildfire Smoke

By Bob Henson

(Photo credit: Christopher Michel / CC BY 2.0)

Articles on U.S. wildfires don’t often show a photo of someone gasping in a hospital bed or felled by a heart attack. Yet an increasing body of evidence suggests that the biggest societal impacts of increasing wildland fire are happening in our own bodies, the result of tiny particulates spewed in vast amounts.

Millions of people across the western U.S. coughed and hacked their way through the summer and autumn of 2020, when some of the region’s worst fires on record ripped across the landscape. It’s too soon to know the full range of health consequences from that summer’s blazes, but there’s already evidence now in peer review that more than 100 deaths may be attributable to 2020’s late-summer smoke in Washington state alone. If another early estimate is on target, the smoke may have contributed to between 1,200 and 3,000 premature deaths in California among people 65 and older.

Research on wildfire smoke and health is advancing hand in hand with the threat itself. The western fires of 2020 came soon after several disastrously hot, fiery years in California, which spawned a grim bumper crop of case studies. Meanwhile, an expanding array of satellite imagery is helping pinpoint where and when smoke is being emitted and transported. That’s helping scientists determine the number of people hospitalized or killed in a given area as a consequence of smoke.“I think one of the biggest developments of the last three years has been the intense interest on the part of government, health organizations, media, and the public on the whole topic of fire smoke and health,” says Wayne Cascio, who directs EPA’s Center for Public Health and Environmental Assessment. “It’s been raised to such a high level nationally and even globally that it’s motivating a lot of action to support science and to answer key questions.”

Among other relevant issues, smoke appears more likely than the fires themselves to affect communities already struggling with socioeconomic and race-based health disparities.

“Nearly all the media attention during wildfires focuses on the lives and property directly in harm’s way. These are important and tragic impacts, but are likely only a very small portion of the overall societal impacts of wildfire,” says Marshall Burke, an associate professor of Earth system science at Stanford University. Burke is lead author of a 2021 paper in the Proceedings of the National Academy of Sciences (PNAS) on the evolving, multipronged threat posed by increasing U.S. wildfires.

In an October 2020 policy brief, Burke and two Stanford colleagues noted that wildfire smoke likely is responsible for 5,000 to 15,000 U.S. deaths in a typical year, and that especially smoky years like 2018 or 2020 will have a much higher death toll.

“Our research suggests that many more people likely perish from smoke exposure during large fire events than perish directly in the fire, and many more people are made sick,” Burke says.

Fine particulates: minuscule and merciless

The most concerning byproducts of wildland fire are the smallest particulates routinely tracked by EPA: PM2.5, those no larger than 2.5 microns in diameter. These have long been linked to increased risk of illness and death, as they’re small enough to enter lungs and also the bloodstream, thus affect-

(Image Credit: Tiana Huddlestun/USFS)

Firefighters in California September 2020 The interagency firefighting group, Lassen Hotshots, holds the line on September 24, 2020, against California’s largest fire by far in 89 years of modern record keeping: the one-million-acre August Complex.

ing both cardiovascular and respiratory systems. occur. “Nobody wants to change the Clean Air Act,” says

Globally, more than 4 million deaths per year are estimated Wara, but “everybody recognizes we need to change how we to be triggered by outdoor air pollution. The actual toll could manage this.” be twice that, if one recent study is correct. A large share of those fatalities can be chalked up to PM2.5. Smoke, health, and the environmental equity

Although PM2.5 from pollution has decreased by more implications than 40% in the U.S. since 2000, wildfire-related PM2.5 is on Wildfires are seldom viewed through the lens of environthe increase. Burke and colleagues found that the fraction mental justice. The reason, in part, is that most immediate of total nationwide PM2.5 that originates from wildfire has impacts of U.S. wildfire, including injuries and deaths as jumped from around 10% in 2010 to around 25% today. In well as structural damage, tend to affect exurban and rural parts of the West, they estimate, fires now produce up to communities in the West that are largely white. For exam50% of all PM2.5 – in other words, as much as all pollution ple, the Camp Fire of November 2018 – California’s deadlisources together. est (85 deaths) and most destructive modern-day fire (18,804

Startlingly, the immense structures lost) – hit hardest in the amounts of smoke thrown into town of Paradise, which was 92% the air by wildland fire aren’t cov- white as of the 2010 census. ered at all under the federal Clean The impacts of smoke, which Air Act: As their very name sug- can extend hundreds of miles gests, wildfires are uncontrollable from a major fire, are another and thus not subject to regulation. matter. Easterly winds pushed

At the same time, the periodic smoke from the Camp Fire into controlled burning of fire-prone the Bay Area for two weeks on areas in order to forestall much end, giving San Francisco six of bigger fires – a practice used by its 10 worst PM2.5 days up to that Indigenous people for centuries, (Image credit: Wikimedia Commons/Test Subject 51.) point in data going back to 1999. and more recently taken up by In the East Bay city of Vallejo, as federal, state, local, and private land managers – does fall under Plume smoke above Paradise, California in 2018 A massive smoke plume looms above Paradise, California, on November 8, 2018, the first day of the catastrophic reported by KQED public radio, the levels of PM2.5 soared to 247 Clean Air Act regulation of both Camp Fire. This photo was taken from atop Butte Hall at micrograms per cubic meter (μg/ PM2.5 and ozone. California State University, Chico. m3 ) – far above the federal 24-

The paradoxical upshot: clean- hour standard of 35, and closer air law is limiting our ability to quell wildfires that are poten- to levels observed on a bad day in pollution-choked cities tially riskier than controlled burns to air quality and collec- such as Beijing or Delhi. Vallejo is one of the state’s most tive health. This conflict is especially pronounced in regions diverse cities: 33% white as of the 2010 census. already struggling to meet national ambient air quality attain- Equity comes into play even more when smoke worsens ment levels because of pollution unrelated to fire. health conditions that are already more prevalent in low-

It’s a conundrum that forest managers and air quality er-income locations, including some communities of color. regulators are increasingly pondering, according to Stan- One 2016 study in northern California found that people in ford-based research scholar and environmental law expert lower-income zip code areas were disproportionately likely Michael Wara, who coauthored the PNAS paper. on wildfire smoke days to visit emergency rooms for asthma

“Doing prescribed fire on a site in a way that prevents a complications. catastrophic wildfire dramatically reduces emissions of PM “Health insurance may be a key factor,” says Colleen Reid per acre. It’s an order of magnitude difference,” says Wara. of the University of Colorado, lead author of that study and “You burn so much less material when you just come in and of a 2016 research review on wildfire smoke and health that burn the forest floor and [not] the large trees.” she expects soon to update. Reid points out that one study

Currently, a land manager – whether a private owner, a from Canada, where universal health care access is the norm, government entity, or an Indigenous tribe – can apply for found no differential impact from wildfire smoke based on permission to exceed 24-hour guidelines for PM2.5 and ozone socioeconomic status, whereas several U.S. studies have with a single prescribed burn. However, a season’s worth of found such effects. controlled burning could still run up against annual PM2.5 People in lower-income areas may also be more vulnerable and ozone limits, even if these burns help avoid an eventual to smoke impacts simply because of their housing. Especially wildfire that would be truly catastrophic. when prolonged, wildfire smoke can easily infiltrate homes

Wara is part of an embryonic effort to examine how the and compromise indoor air quality. Clean Air Act could be reinterpreted to balance the relative “At least in California, older housing is much less airtight emission harms from controlled burns versus massive wild- than newer housing stock,” says Wara. Moreover, he adds, fires. “We need to bring realistic versions of land manage- “Wealthy people tend to have the disposable income to drop ment into the models used to evaluate these processes,” Wara a couple hundred dollars on HEPA filters. I know other peosays. ple who suffer terribly through wildfire season. People I

The ultimate air-quality goal, he adds, is to reduce expo- know are taping plastic sheeting over their windows. Even sure to harmful smoke in all the ways such exposures can if you put a box fan together with a filter, if your house isn’t

tight, the smoke just gets in.”

There’s much yet to learn about wildfire smoke and health disparities. A study published in Science Advances on April 28 found that nearly all U.S. sources of PM2.5 emissions disproportionately affect people of color. However, the study did not cover emissions from wildfires.

Zeroing in on longevity and health impacts

Back in 1994, the landmark “Six Cities” study from the Harvard School of Public Health revealed pollution’s terrible toll: long-term exposure to high levels of PM2.5, even in cities that met existing air quality standards, could shorten life expectancy by up to three years. Reducing PM2.5 gives the most

(Image credit: EPA.)

Particulate matter 2.5 The tiny bits of particulate matter known as PM2.5 are smaller than 2.5 microns in diameter – less than 5% of the width of a strand of human hair.

health benefit for each dollar of pollution control.

Although PM2.5’s biggest threat is to the cardiovascular system, such effects have been difficult to nail down for wildfire smoke, according to Reid. “A few more recent studies have found more significant relationships,” Reid says. “There’s a lot of statistical methodology differences among different groups, so we need to do some more work.”

There are also emerging signs that PM2.5 from wildland fires may be more health-hazardous than other PM2.5, at least in some cases. A recent Nature Communications study led by Rosana Aguilera, a postdoctoral researcher at the Scripps Institution of Oceanography, examined 14 years of Southern California fires. The authors found up to a 10% increase in respiratory hospitalizations for every 10 μg/m3 increase in wildfire-specific PM2.5, compared to a 1.3% increase for non-wildfire PM2.5.

Similarly, a 2020 study led by Daniel Kiser of the Desert Research Institute found that asthma-related visits to urgent care centers and emergency rooms in the Reno area were boosted by an additional 6.1% for every 5 μg/m3 increase in PM2.5 for cases when wildfire smoke was present compared to when it was not present.

Not all studies have found such differences, however, perhaps because of methodological and regional variations. Health impacts from wildfire smoke may also vary based on exactly what’s being consumed by a wildfire (oak, pine needles, eucalyptus, or peat, to name just a few), and on whether a fire is smoldering versus raging. Such nuances are “pretty challenging to investigate,” says the EPA’s Cascio, “but certainly the lab data suggest there may be differences.”

Along with its growing body of research on wildfire smoke and health, including new efforts focused on public communication and intervention, EPA launched its Smoke Sense app (available through Android and iOS systems) in 2017. More than 40,000 users have downloaded Smoke Sense, which provides current fire and air-quality data and hourly forecasts of smoke and ozone. People can also gauge their own vulnerability to smoke impacts and anonymously report any symptoms via the app.

Bracing for more fire and smoke this summer

The accumulating research on wildfires and health could lead to a transformation in how we view the infernos that are becoming more widespread across ever-more-intense fire seasons. Human-produced global heating is not only raising temperatures – it’s also raising the stakes for wildfire risk. In a warming climate, landscapes can dry out more readily even where precipitation trends aren’t changing.

“Among the many processes important to California’s diverse fire regimes, warming-driven fuel drying is the clearest link between anthropogenic climate change and increased California wildfire activity to date,” concluded Park Williams of Columbia University in a 2019 paper.

Many Westerners are approaching the summer of 2021 with trepidation. As California’s wet season draws to a disappointing close, the state is now virtually certain to lock up its second driest pair of water years in records going more than a century, behind only 1975-77, according to Bay Area expert Jan Null of Golden Gate Weather Services.

Not all dry years are particularly fiery, noted Null in a blog post. Less than 34,000 acres burned in California in 1991, even after two relatively dry winters in a row. On the whole, though, Null calls the relationship between drought and California fire “compelling.”

By the end of April – weeks ahead of the norm – serious fires had already erupted in California, Arizona, and New Mexico. NOAA’s latest seasonal drought outlook, issued April 15 and extending through July, calls for drought to persist or develop across the entire contiguous U.S. west of the Rockies except for western Washington and far northwest Oregon.

About the Author

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance venues. Bob is the author of “The Thinking Person’s Guide to Climate Change” and of “The Rough Guide to Climate Change,” a forerunner to it, and of “Weather on the Air: A History of Broadcast Meteorology”, and coauthor of the introductory textbook “Meteorology Today”. A native of Oklahoma City, he earned a bachelor's degree in meteorology and psychology from Rice University and a master's degree in journalism, with a focus on meteorology, from the University of Oklahoma.