Smoke exposure from California’s wildfires linked to 52,000 early deaths, study says

When large swaths of the East Coast were shrouded in wildfire smoke last summer, scientists in California grimly joked that maybe, finally, power brokers in New York and Washington, D.C. would be spurred to act on the burning issue that has long plagued the West Coast. Despite wildfire seasons that regularly burn hundreds of thousands of acres in California alone each year, researchers know relatively little about the long-term effects of chronic wildfire smoke on the body, and funding to reduce the known harms of exposure is scarce.

In a paper published Friday in Science Advances, researchers at UCLA Fielding School of Public Health tried to chip away at that knowledge gap. They estimated that somewhere between 52,480 and 55,710 people in California died prematurely between 2008-2018 due to chronic exposure to the dangerous particulate matter in wildfire smoke. And the economic impact of those deaths was at least $432 billion.

“It’s overwhelming to really see that amount of death,” said David Rojas-Rueda, an assistant professor of environmental and occupational health at Colorado School of Public Health who was not involved in the study. “This is a very important step forward.”

Ideally, scientists could measure the impact of repeated wildfire smoke exposure directly, by following real people living in wildfire-prone areas in a longitudinal cohort study, experts said. But that would take significant resources. So Michael Jerrett, a researcher and environmental health professor at UCLA, simulated exposure instead. He and his colleagues used a concentration-response model to estimate the relationship between air pollutant concentration — from the Environmental Protection Agency’s Community Multiscale Air Quality Modeling System — and health outcomes.

It’s a well-established approach, Rojas-Rueda said. “Health impact assessments are not intended to be precise,” Rojas-Rueda said. “Rather, the intention is to give you a sense of the magnitude of a problem.”

Previous studies have attempted to quantify the impact of wildfire smoke exposure on health and mortality. Most look at short, acute exposures — measuring, for example, hospital admissions in the days after a bad fire, and many are limited to county-level estimates. But in their analysis, the UCLA researchers found that every single zip code in California experienced wildfire smoke during every single year of their study. This meant they could consider the smoke as a chronic exposure, rather than as a one-time occurrence.

Because they took the chronic effect of particulate exposure into account, the estimate of more than 52,000 deaths includes the way it may contribute to other diseases, Jerrett said.

Teeny, tiny, toxic particles called PM2.5 can float in the air for long periods of time, generated by industrial pollution, vehicle exhaust, and burning other fuels like wood. Most research on the health effects of inhaling PM2.5 look at its effects regardless of the source. But the researchers worked with Joseph Wilkins of Howard University, an expert in developing air quality models, to isolate geographic exposure to PM2.5 from wildfire smoke. By simulating atmospheric chemistry, Wilkins and the team had the ability to “turn off” other types of emissions in their calculations.

“When we started seeing the magnitude of these numbers, we were definitely surprised,” said Jerrett. He and his colleagues believe previous analyses may have underestimated the impact that wildfires have on mortality because they haven’t approached it as a chronic exposure.

Longitudinal follow-ups to health impact assessment studies are still possible, if expensive, Rojas-Rueda said. There are ongoing cohort studies that could start collecting data on wildfire exposure, like the National Institute of Health’s All of Us program or the Nurses’ Health Study, he pointed out.

But the need for more research doesn’t preclude the need for action now, experts said. Risk management strategies and communication are critical. Reducing people’s exposure can mean small-scale solutions like building homes with better windows and less flammable materials, experts said, but also addressing larger societal issues like homelessness and, of course, climate change.

State and federal lawmakers have committed to spend around $6.7 billion over the next few years on wildfire mitigation, but Jerrett says it isn’t enough when compared to the hundreds of billions lost when people suffer the health consequences of wildfire exposure.

The early death estimates are just another addition to the layers of data we already have on the harms of uncontrolled pollution, Rojas-Rueda added.

“We need more change, and speed in that change,” he said. Another fire season has begun on the West Coast, “and next year, we’ll be talking about this again.”