The smoke from wildfires already neutralizes decades of improvements in air quality across large areas of the United States.
For years, environmental policies reduced pollution through cleaner engines and regulated power plants.
However, this progress is being reversed by a factor that is increasingly frequent, intense, and persistent: wildfire smoke.
This is revealed by an analysis from Harvard University conducted between 1997 and 2020 in the western U.S.
This detected that around 65% of emissions from large wildfires were directly linked to the temperature increase caused by human activity.
Therefore, this is not a temporary trend but a structural change.
The research, led by Loretta Mickley from Harvard’s School of Engineering and Applied Sciences, tracked the path of smoke from the forests of California to agricultural valleys, urban areas, and interior desert regions.
Warming also intensifies fires
Warming not only dries landscapes; it makes them more flammable.
Researchers estimated that between 60% and 82% of the area burned since the early 1990s can be explained by the temperature increase associated with climate change.
In central and southern California, approximately one-third of the land scorched is due to this factor. Wildfires caused by lightning show an even clearer relationship with warming.
Hotter air increases the vapor pressure deficit, a measure of how much moisture the atmosphere extracts from plants and soils. Pine needles, shrubs, and grasses burn better when dry.
To capture this process, the team combined weather records from several decades with satellite data on greenness and water stress of vegetation.
Already in 2016, a previous study showed that drying doubled the total area burned since 1984 in the western forests.
The public health impact of wildfire smoke
Wildfire smoke contains PM2.5, particles so small that they penetrate the lungs and can reach the bloodstream.
Exposure is associated with respiratory and cardiovascular problems and an increase in hospitalizations.
During the same period when industrial and traffic pollution fell by around 44%, the contribution of smoke went in the opposite direction.
In the last decade analyzed, 58% of the increase in PM2.5 from smoke was linked to global warming.
In northern California, Oregon, Washington, and Idaho, climate-driven smoke accounted for between 44% and 66% of the total PM2.5 inhaled by the population.
Brief but intense peaks of PM2.5 can trigger asthma attacks, overload the cardiovascular system, and disproportionately affect older people, children, and pregnant women.
The necessary adaptation measures
At the local level, there are margins for action to reduce exposure to wildfire smoke. Communities can implement various strategies:
- Expand smoke prediction systems
- Enable clean air shelters
- Prepare schools and health centers for weeks of poor air quality
- Improve filtration in buildings and the use of portable purifiers
- Adjust work schedules for outdoor jobs
Forest management offers known but difficult-to-apply tools.
Prescribed burns, conducted under controlled conditions, reduce accumulated fuel and can moderate the behavior of future fires.
The problem is time: safe windows for burning are short and require smoke management plans, clear communication with local communities, and coordination with indigenous peoples, who have been using fire as a tool for centuries.
Currently, treating wildfire smoke as an exceptional event no longer works.
It is increasingly resembling a recurrent and predictable risk that should be integrated into health planning.
