Wildfire smoke impact far greater than estimates: thousands killed

Wildfires burning across Canada and the Western United States are spewing smoke over millions of Americans, with health impacts far greater than scientists previously estimated.

Although wildfires have long been part of life in the Western U.S., warmer, drier conditions are fueling bigger blazes that occur more often and for longer. Smoke from these blazes is spreading farther and lingering longer than in the past. In a Sept. 18 study in Nature, Stanford University researchers estimate that continued global warming could lead to about 30,000 additional deaths each year nationwide by 2050, as climate-driven increases in fire activity generate more smoke pollution across North America.

The researchers found no U.S. community is safe from smoke exposure. When monetized, deaths related to wildfire smoke could reach $608 billion in annual damages by 2050 under a business-as-usual emissions scenario where global temperatures rise about 2 degrees Celsius above pre-industrial levels. That estimated toll surpasses current estimates of economic costs from all other climate-driven damages in the U.S. combined, including temperature-related deaths, agricultural losses, and storm damage.

“What we see, and this is consistent with what others find, is a nationwide increase in wildfire smoke,” said lead study author Minghao Qiu. “There are larger increases on the West Coast, but there’s also long-range transport of wildfire smoke across the country, including massive recent smoke events in the Eastern and Midwestern U.S. from Canadian fires.”

Deaths from wildfire smoke result from inhaling a complex mix of chemicals. Wildfires can expose large numbers of people to these toxic pollutants for days or weeks at a time, contributing to deaths up to three years after the initial exposure, according to the new study.

Within wildfire smoke pollution, researchers often focus on fine particulate matter, known as PM2.5, which penetrates the lungs and enters the bloodstream. While the health effects of PM2.5 from other sources are well studied, less is known about the specific dangers of PM2.5 from wildfire smoke. Some recent research shows that wildfire smoke can contain a range of toxic chemicals harmful to human health. Qiu, Burke, and colleagues used U.S. death records to assess these additional risks from smoke.

The researchers combined county-level data on all recorded U.S. deaths from 2006 to 2019 with measurements of ground-level smoke emissions, wind variation, and the movement of airborne particulate matter, using machine learning to predict how wildfire emissions changes in one area affected smoke concentrations in another. They linked changes in smoke concentrations to variation in historical mortality and used global climate models to project future fire activity, smoke levels, and health impacts under different warming scenarios through 2050.

The results show that excess deaths from smoke PM2.5 exposure under a business-as-usual emissions scenario could increase more than 70% to 70,000 per year from roughly 40,000 annual deaths attributed to smoke from 2011 to 2020. The largest projected increases in annual smoke exposure deaths occur in California (5,060 additional deaths), New York (1,810), Washington (1,730), Texas (1,700), and Pennsylvania (1,600).

By quantifying economic damage from smoke-related deaths, the findings uncover a hidden tax on families and businesses. The researchers found that even if the world cuts emissions rapidly enough to stabilize global temperatures below 2ºC by the end of the century, deaths from climate-driven smoke exposure in the U.S. alone would likely still exceed 60,000 per year by 2050.

“If you look at the leading climate impact assessment tools that are used to inform policy, none of them incorporate how changes in climate could influence wildfire smoke and related human mortality,” Qiu said. “Our study shows climate models are missing a huge part of the climate impacts in the U.S. – it’s like leaving the main character out of a movie.”

(Adapted from materials provided by the Stanford Doerr School of Sustainability.)