Climate Matters
Wildfire Smoke: Nationwide Health Risk
Wildfire smoke can travel far and harm health. We can expect to breathe in more of it in a warming climate.
Climate Matters•August 20, 2025
Climate Change Worsens Wildfire Smoke
KEY FACTS
Wildfire smoke pollution has surged in recent years, putting health at risk across the U.S. Emerging research shows that climate change is making it worse.
Per-person exposure to harmful wildfire smoke in the U.S. was four times higher during 2020-2024, on average each year, than during 2006-2019.
Wildfire smoke can spread hundreds or even thousands of miles away, harming health far from areas with active fires.
New research shows that wildfire smoke caused 164,000 premature deaths in the U.S. from 2006 to 2020 — and that climate change accounted for about 15,000 of those smoke-related deaths.
Heat-trapping pollution fuels the hot, dry conditions that help fires spark and spread.
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Americans are breathing record levels of wildfire smoke
Human-caused climate change has fueled more fire activity in the western U.S., increased the frequency and intensity of fire weather, and expanded burned areas across the U.S.
Emerging research shows that climate change is also making wildfire smoke and the related health effects worse.
Per-person exposure to harmful wildfire smoke in the U.S. was four times higher during 2020-2024, on average each year, than during 2006-2019. That’s according to data from Stanford University’s Environmental Change and Human Outcomes Lab.
Wildfire smoke can spread hundreds or even thousands of miles away, harming health far from areas with active fires.
Smoke exposure shattered records in 2023, partly because of smoke from Canada’s worst wildfire season on record traveling over densely populated areas of the eastern U.S.
In 2025, Canadian fires have so far burned an area more than double the country’s 10-year average — making this the country’s second-worst wildfire season and again spreading unhealthy smoke to the Upper Midwest and parts of the Northeast.
Wildfire smoke affects air quality across the U.S.
The U.S. regions with the largest burned areas — the West and Northwest, and parts of Arizona — generally experience the most wildfire smoke days each year.
Some counties in California, Oregon, Arizona, Texas, Louisiana, and Florida experience an average of 90-111 wildfire smoke days each year.
Although wildfire smoke is most acute in the western U.S., it’s a nationwide air quality issue. Every county in the contiguous U.S. now sees at least 16 wildfire smoke days each year.
Outside the West and Southwest, large areas of the Northern Rockies and Plains as well as the central and southern U.S. experience at least two months’ worth of wildfire smoke days each year.
More wildfire smoke deaths due to climate change
New research shows that fine particulate matter (or PM2.5) in wildfire smoke caused nearly 164,000 deaths in the U.S. over the 15 years ending in 2020. This health burden extended across the entire country, including states far from the center of fire activity in the U.S. and Canada.
Heat-trapping pollution and the resulting rise in hot, dry fire weather conditions worsened this health burden. According to the same study, human-caused climate change contributed to about 15,000 of these smoke-related deaths.
This climate change-fueled health burden was highest in California, Oregon, and Washington. On average, climate change added a total of 580 more smoke-related deaths annually across these states, accounting for approximately one-quarter to one-third of all such deaths in each state.
Smoke travels far, spreading health risks from coast to coast
Across the U.S., the majority of wildfire smoke PM2.5 experienced locally comes from distant fires — whether in other counties (87%) or other states (60%). The prevalence of smoke originating from other counties and states surged from 2006 to 2020, especially across the Pacific Northwest, California, Idaho, and Montana.
Although most large fires occur in the western U.S., about three-quarters of smoke-related mortality and asthma morbidity occurs in other U.S. regions due to long-range smoke transport and high population density in eastern U.S. regions.
The rise in wildfire smoke since 2016 has either stalled or reversed decades-long air quality improvements in 30 U.S. states. Air quality has eroded the most in California, Oregon, and Washington, where conditions reflect both local fires and fires in western Canada.
If these trends continue, they threaten to undo decades of air quality improvements under the Clean Air Act.
How wildfire smoke harms health
Wildfire smoke is a complex mix of pollutants, but fine particulate matter (PM2.5) accounts for about 90% — and is the main threat to human health.
When people breathe in wildfire smoke, these tiny particles can make their way deep into the lungs and even into the bloodstream, causing a range of health effects from minor irritation to serious cardiovascular and respiratory illness.
Wildfire smoke can also affect learning outcomes. A recent study found that exposure to PM2.5 from wildfire smoke corresponds to lower test scores among U.S. students aged eight to 14 years.
Wildfire smoke is hazardous for everyone but some people face higher risks, including the elderly, pregnant people, children, and those with chronic conditions such as asthma, COPD, and heart disease.
Learn more: Climate Change & Children's Health: Air Quality
Some people, including wildland firefighters, first responders, and outdoor workers, also face higher risks of exposure to fire and smoke during wildfire outbreaks.
Additionally, some U.S. regions — including the North Central, South, Southeast, and West — face higher overlapping health burdens from both extreme heat and wildfire smoke.
LOCAL STORY ANGLES
Are wildfires currently affecting air quality in your area?
Find wildfire smoke tracking maps through NOAA’s Office of Satellite and Product Operations and AirNow’s Fire and Smoke Map. Check the National Weather Service’s fire hazard forecast maps for fire watches or warnings across the U.S. For seasonal forecasts and future projections of fire activity, Climate Toolbox's Climate Mapper tool provides experimental two-week fire danger forecasts for the contiguous U.S.
Where has wildfire smoke had the biggest impact so far this year?
The Mortality Estimation Tool, an experimental map tool from NOAA’s Northeast Regional Climate Center and Cornell University, estimates the total wildfire smoke PM2.5 concentrations and related deaths by county across the U.S. Use the map options to display conditions for a specific date, the last 30 days, or year to date.
CONTACT EXPERTS
Carlos Gould, PhD (he/him)
Assistant Professor
University of California, San Diego
Related expertise: effects of wildfire smoke exposure; mortality burden from wildfire smoke
Contact: cagould@health.ucsd.edu
*Available for interviews in English and Spanish
Jennifer Stowell, PhD
Assistant Professor
Global, Environmental, and Occupational Health
University of Maryland School of Public Health
Related expertise: effects of wildfire smoke exposure on population health, pregnancy complications, birth outcomes, and children
Contact: stowellj@umd.edu
Nicholas Nassikas, MD
Assistant Professor of Medicine
Beth Israel Deaconess Medical Center
Related expertise: intersection of climate change and respiratory disease
Contact: nnassika@bidmc.harvard.edu
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
Cumulative daily PM2.5 exposure data from 2006-2024 were obtained from the authors of Childs et al. (2024)
Daily smoke PM2.5 predictions by county from 2006-2020 come from Childs et al., 2022. Any non-zero day was considered a wildfire smoke day and was used to calculate the average annual predicted days with wildfire-related smoke by county.
Estimates of wildfire smoke PM2.5-related mortality for the contiguous U.S. from 2006-2020 are from Law et al., 2025. Cumulative total wildfire PM2.5 mortality in each state (2006-2020) are listed in Supplementary Table 5.
Special thanks to Marissa Childs and Nicholas Nassikas for their help with data for this release.