Study shows controlled burns can reduce wildfire intensity and smoke pollution
Stanford University
As wildfires increasingly threaten lives, landscapes, and air quality across the U.S., a Stanford-led study published in AGU Advances June 26 finds that prescribed burns can help reduce risks. The research reveals that prescribed burns can reduce the severity of subsequent wildfires by an average of 16% and net smoke pollution by an average of 14%.
“Prescribed fire is often promoted as a promising tool in theory to dampen wildfire impacts, but we show clear empirical evidence that prescribed burning works in practice,” said lead author Makoto Kelp, a postdoctoral fellow in Earth system science at the Stanford Doerr School of Sustainability. “It’s not a cure-all, but it’s a strategy that can reduce harm from extreme wildfires when used effectively.”
Experts consider prescribed burns an effective strategy to reduce the threat of wildfires, and nearly $2 billion of federal funding had been set aside to conduct these and similar treatments to reduce hazardous fuel. Still, the use of prescribed burning in western states has expanded only slightly in recent years. Little research exists to quantify its effectiveness, and public opinion remains mixed amid concerns that prescribed burns can lead to smoky air and escaped fires.
Data-driven fire strategy
At Stanford, Kelp is working with climate scientist Noah Diffenbaugh and environmental economist Marshall Burke through the National Oceanic and Atmospheric Administration Climate and Global Change Postdoctoral Fellowship Program. Using high-resolution satellite imagery, land management records, and smoke emissions inventories, the research team compared areas treated with prescribed fire between late 2018 and spring 2020 to adjacent untreated areas that both later burned in the extreme 2020 fire season. The analysis found that areas treated with prescribed fire burned less severely and produced significantly less smoke.
That finding is particularly important given the growing recognition of wildfire smoke as a major public health threat. Fine particulate matter (PM2.5) from wildfires has been linked to respiratory and cardiovascular problems and is increasingly driving poor air quality across the U.S.
“People often think of wildfires just in terms of flames and evacuations,” said Burke, an associate professor of environmental social sciences in the Doerr School of Sustainability. “But the smoke is a silent and far-reaching hazard, and prescribed fire may be one of the few tools that actually reduces total smoke exposure.”
Not all treatments are equal
The study also highlights a key nuance: the authors found that prescribed fires were significantly more effective outside of the wildland-urban interface (WUI)—the zones where homes meet wildland vegetation—than within it. In WUI areas, where agencies often rely on mechanical thinning due to concerns about smoke and safety, fire severity was reduced by just 8.5%, compared to 20% in non-WUI zones.
“We already know that population is growing fastest in the areas of the wildland-urban interface where the vegetation is most sensitive to climate-induced intensification of wildfire risk,” said Diffenbaugh, the Kara J Foundation Professor in the Stanford Doerr School of Sustainability and the Kimmelman Family Senior Fellow at the Stanford Woods Institute for the Environment. “So, understanding why the prescribed fire treatments are less effective in those areas is a key priority for effectively managing that intensifying risk.”
Smoke tradeoffs and policy implications
The study addresses concerns about smoky air from prescribed burning, finding that the approach produces only about 17% of the PM2.5 smoke that would be emitted by a wildfire in the same area. The researchers estimate that if California met its goal of treating one million acres annually with prescribed fire, it could cut PM2.5 emissions by 655,000 tons over five years—more than half of the total smoke pollution from the state’s devastating 2020 wildfire season.
The authors note that their findings likely represent a conservative estimate of the benefits of prescribed fire, as such treatments can have protective spillover effects on surrounding untreated areas.
“This kind of empirical evidence is critical for effective policy,” said Kelp. “My hope is that it helps inform the ongoing conversation around prescribed fire as a potential wildfire mitigation strategy in California.”
Coauthors of the study also include Minghao Qiu of Stony Brook University, Iván Higuera-Mendieta, a PhD student in Earth system science at Stanford; and Tianjia Liu of the University of British Columbia.
Burke is also a senior fellow at the Stanford Woods Institute for the Environment, the Freeman Spogli Institute for International Studies, and the Stanford Institute for Economic Policy Research (SIEPR); an associate professor (by courtesy) of Earth system science; and a member of Bio-X and the Wu Tsai Neurosciences Institute.
The study was funded by the National Oceanic and Atmospheric Administration and Stanford University.
Journal
AGU Advances
Article Title
Effect of Recent Prescribed Burning and Land Management on Wildfire Burn Severity and 1 Smoke Emissions in the Western United States
Article Publication Date
26-Jun-2025
Fire smoke exposure may alter the immune system, even in healthy individuals
Harvard T.H. Chan School of Public Health
Key points:
- Healthy adults exposed to fire smoke—which can be composed of gases, particulate matter, and toxins—showed alterations to their immune systems, including changes in the regulation of genes associated with asthma and allergies, and in immune cells that play a key role in fighting pathogens, compared to adults who had no exposure to fire smoke.
- The study is the first to examine the specific immune mechanisms associated with fire smoke exposure, showing cellular-level changes related to smoke’s known negative impacts on respiratory, cardiac, neurological, and pregnancy outcomes.
- According to the researchers, the findings may pave the way for new therapeutics to mitigate, or prevent altogether, the health effects of smoke exposure and environmental contaminants.
Boston, MA—Exposure to fire smoke—which can be composed of particulate matter, gases, materials from buildings such as perfluoroalkyl and polyfluoroalkyl substances (PFAS), toxic metals, and carcinogenic compounds—may alter the immune system on a cellular level, according to a new study led by researchers at Harvard T.H. Chan School of Public Health. The study is the first to examine the specific cellular changes associated with fire smoke exposure, documenting how smoke can damage the body through the immune system.
“We’ve known that smoke exposure causes poor respiratory, cardiac, neurological, and pregnancy outcomes, but we haven’t understood how,” said corresponding author Kari Nadeau, John Rock Professor of Climate and Population Studies and chair of the Department of Environmental Health. “Our study fills in this knowledge gap, so that clinicians and public health leaders are better equipped to respond to the growing threat of difficult to contain, toxic wildfires.”
The study was published June 26 in Nature Medicine.
The researchers collected blood from two cohorts matched by age, sex, and socioeconomic status: 31 smoke-exposed adults, both firefighters and civilians, and 29 non-smoke-exposed adults. None of the participants had an acute or chronic condition, and none were taking immunomodulatory drugs at or before the time of the blood draw, which took place within one month after participants had been exposed to fire smoke.
Using cutting-edge single-cell -omic techniques—epigenetic assays and mass cytometry—and bioinformatic analytical tools, the researchers examined and analyzed individual cells within each blood sample.
The study found several cellular-level changes in the smoke-exposed individuals compared to the non-smoke-exposed individuals. Smoke-exposed individuals showed an increase in memory CD8+ T cells (a type of immune cell critical to long-term immunity against pathogens) and elevated activation and chemokine receptor biomarkers (indicators of inflammation and immune activity) within multiple cell types. Additionally, those who had been exposed to smoke showed changes in133 genes related to allergies and asthma, and more of their immune cells were bound with toxic metals, including mercury and cadmium.
“Our findings demonstrate that the immune system is extremely sensitive to environmental exposures like fire smoke, even in healthy individuals,” said lead author Mary Johnson, principal research scientist in the Department of Environmental Health. “Knowing exactly how may help us detect immune dysfunction from smoke exposure earlier and could pave the way for new therapeutics to mitigate, or prevent altogether, the health effects of smoke exposure and environmental contaminants.”
The researchers also noted that the study could help inform environmental and public health policies and investments. “Knowing more about exactly how smoke exposure is harming the body, we may increase public health campaigns about the dangers of smoke exposure and the importance of following evacuation procedures during wildfires,” Nadeau said. “We may also reconsider what levels of smoke exposure we consider toxic.”
Other Harvard Chan co-authors included Abhinav Kaushik, Olivia Kline, Xiaoying Zhou, and Elisabeth Simonin.
The study was funded by the National Institute of Environmental Health Sciences (R01 ES032253), the National Heart, Lung, and Blood Institute (P01 HL152953, T32HL007118), the National Institute of Allergy and Infectious Diseases (U19AI167903), the San Francisco Cancer Prevention Foundation, the Asthma and Allergic Diseases Cooperative Research Center, and the Keck Foundation.
“Immune impacts of fire smoke exposure,” Mary M. Johnson, Abhinav Kaushik, Olivia A. Kline, Eric M. Smith, Xiaoying Zhou, Yagiz Pat, Laura Buergi, Juan Aguilera, Shifaa Alkotob, Elisabeth M. Simonin, Alberto Favaro, Miguel Couto, Oscar Bennett, R. Sharon Chinthrajah, Ella Parsons, Mohamed Shamji, Marshall Burke, Melissa Bondy, Mubeccel Akdis, Cezmi A. Akdis, Kari C. Nadeau, Nature Medicine, June 26, 2025, doi: 10.1038/s41591-025-03777-6
Visit the Harvard Chan School website for the latest news and events from our Studio.
###
Harvard T.H. Chan School of Public Health is a community of innovative scientists, practitioners, educators, and students dedicated to improving health and advancing equity so all people can thrive. We research the many factors influencing health and collaborate widely to translate those insights into policies, programs, and practices that prevent disease and promote well-being for people around the world. We also educate thousands of public health leaders a year through our degree programs, postdoctoral training, fellowships, and continuing education courses. Founded in 1913 as America’s first professional training program in public health, the School continues to have an extraordinary impact in fields ranging from infectious disease to environmental justice to health systems and beyond
Journal
Nature Medicine
Method of Research
Observational study
Subject of Research
People
Article Title
Immune impacts of fire smoke exposure
Article Publication Date
26-Jun-2025
No comments:
Post a Comment