Warming climate making fine particulate matter from wildfires more deadly and expensive

About 35% of the additional deaths attributed to climate change occurred in 2020, the year of the historic Labor Day fires in the Pacific Northwest as well as major blazes in California, Colorado and Arizona.

The study, led by an Oregon State University researcher and published in Nature Communications Earth & Environment, is the first to quantify how many people are dying because a warming climate is causing fires to send increasing amounts of fine particulate matter into the air, especially in the West.

The scientists estimate that during the study period a total of 164,000 deaths resulted from wildfire PM_2.5, particles with a diameter of 2.5 micrometers or smaller that can be inhaled deeply into the lungs and even enter the bloodstream. They determined that 15,000 of those deaths were attributable to climate change -- meaning that absent climate change, the total would have been 149,000.

The average annual death rate from wildfire PM_2.5 during the study period was 5.14 per 100,000 people; by comparison, that's roughly double the annual U.S. death rate from tropical cyclones such as hurricanes

The research also found a $160 billion economic burden associated with those 15,000 extra wildfire PM_2.5 deaths. Economic burden from mortality considers factors such as productivity losses, health care costs and a concept known as value of a statistical life that assigns a monetary value to reduction in mortality risk.

The study, which looked at mortality risk on a county-by-county basis, showed the economic burden was greatest in California, Oregon and Washington.

"Without efforts to address climate change, wildfires and associated fine particulate matter will continue to increase," said Bev Law, professor emerita in the OSU College of Forestry and the study's leader. "Projections of climate-driven wildfire PM_2.5 across the continental U.S. point to at least a 50% increase in mortality from smoke by midcentury relative to the decade ending with 2020, with resulting annual damages of $244 billion."

Using publicly available datasets, Law and collaborators looked at how much additional area burned and how many people died from climate-change related wildfire PM_2.5 during the 2006-20 study period, integrating climate projections, climate-wildfire models, wildfire smoke models, and emission and health impact modeling.

The authors note that as climate change exacerbates wildfire risk, PM_2.5 emissions from fires have surged to the point that wildfires now account for almost half of all PM_2.5 across the United States and have negated air quality improvements in multiple regions. They also say that absent abrupt changes in climate trajectories, land management and population trends, the impacts of climate change on human health via wildfire smoke will escalate.

"Exposure to PM_2.5 is a known cause of cardiovascular disease and is linked to the onset and worsening of respiratory illness," Law said. "Ongoing trends of increasing wildfire severity track with climate projections and underscore how climate change manifestations like earlier snowmelt, intensified heat waves and drier air have already expanded forest fire extent and accelerated daily fire growth rates."

Researchers at the University of California, Merced, the U.S. Environmental Protection Agency, the Woodwell Climate Research Center and Beth Israel Deaconess Medical Center of Harvard Medical School also took part in the study.