The hills above Santa Barbara, Calif., are shrouded in smoke Dec. 12 from the Thomas Fire. (Robyn Beck/AFP/Getty Images)

As firefighters continue to battle California’s devastating Thomas Fire — now the fourth-largest in state history — a group of scientists presented new results suggesting that air pollution from such massive blazes may be one of their deadliest consequences.

Speaking at the annual American Geophysical Union meeting in New Orleans, the researchers, from Colorado State University and the University of Houston, suggested Thursday that wildfires may be responsible for thousands of U.S. deaths annually due to the tiny pollution particles they put into the atmosphere. Moreover, just as fires are expected to worsen under climate warming, so might these health impacts.

“If this is the new norm for California … and people in California are being exposed to these smoke events regularly, then we would expect this to have an impact on the average lifetime of people in California,” said Jeffrey Pierce, a professor of atmospheric science at Colorado State University who presented his preliminary results at the meeting and a news conference afterward.

Just like smokestacks and tailpipes, wildfires fill the air with the byproducts of combustion, including very dangerous small particles known as PM2.5, which can get into the lungs and bloodstream. A growing body of research has demonstrated that these particles degrade health and contribute to thousands of deaths each year in the United States alone by causing respiratory, cardiovascular and other health problems.

So just how deadly is the smoke from wildfires? While the numbers presented this week are definitely preliminary, they suggest the cost could be severe indeed.

Pierce presented the highest numbers at the meeting. He estimates that between 5,000 and 25,000 people in the United States may die each year at present from PM2.5 that specifically comes from the smoke of wildfires burning in the United States and other nearby countries (such as Canada). But the number of wildfire-linked deaths could triple by the end of the century for high levels of global warming, he has found, based on one climate modeling scenario (which, Pierce emphasizes, is only a preliminary finding and should be replicated by other scientific groups).

That would lead to a situation in which, as other sources of air pollution decline, wildfires become an increasingly dominant overall source of PM2.5.

“Coal plants have gotten cleaner, wildfires have slightly increased over the past decades, so, wildfires are on the verge of becoming, if they haven’t become, the largest source of particulate matter in the U.S.,” said Pierce in an interview.

Pierce’s results, not yet published formally, are similar to those of Ebrahim Eslami, a PhD student at the University of Houston who also presented at the meeting on wildfire-related air pollution deaths. He has found that wildfires and other burning of biomass, such as in the agricultural sector, contribute to around 5,000 deaths per year. That equates to annual economic damages between $40 and $50 billion for the period between 2011 and 2014.

“Billions of dollars, or tens of billions of dollars, that’s the magnitude of the cost caused by wildfires due to health impact incidence,” Eslami said.

The studies include not only the effects of raging wildfires, but also controlled burns, in which forest managers deliberately light fires to burn away some of the fuel and reduce the danger of more dangerous outbreaks later. The health effects are of course not evenly distributed — they are the worst in areas closest to large wildfires, such as California, the Pacific Northwest and U.S. southeast.

While Pierce’s and Eslami’s results are not yet formally published, they don’t sound so different from a just published result from a group of scientists with the U.S. Environmental Protection Agency and several Australian institutions. These researchers found that “short term” premature deaths tied to wildfire air pollution in the United States from 2008 through 2012 numbered between 1,500 and 2,500 each year. They calculated that the economic toll, meanwhile, was tens of billions each year.

And these were only short-term effects — over the longer term, the researchers calculated even more severe numbers.

Other recently published work has found that the air pollution contributed by wildfires has been greatly underestimated and that in the western United States during wildfire seasons between 2004 and 2009, fires contributed 12 percent of the total PM2.5 concentrations in the atmosphere, and far more than that on days with particularly poor air quality. The research projected that this situation would get considerably worse due to climate change.

Many health outcomes less severe than death are also triggered by wildfire smoke, particularly in the immediate vicinity of fires, such as asthma attacks and hospital trips for a variety of conditions.

“For a severe smoke event, asthma inhaler refill rates could double across large populations,” said Katelyn O’Dell, a researcher at Colorado State who is working with Pierce studying the health effects of wildfires, in a statement.

Granted, all of these findings should be taken cautiously, because this research is fairly novel. Moreover, researchers acknowledge that wildfire smoke differs in complex ways from other types of air pollution — and indeed, depends on where wildfires occur, and what they consume.

“What burns matters,” said Manvendra Dubey, a researcher at Los Alamos National Laboratory, who is also working on the problem of wildfire smoke and its consequences. Dubey underscored the complex chemistry of the smoke that emanates from different types of fires at the New Orleans meeting.

So there is much more to learn about the dangers of wildfire smoke — but based on the little we know so far, it sounds like a serious threat, and one that could grow even worse in the future.

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