A new study reveals that over the past 30 years, forest fires in the western U.S. have spread 16,000 more square miles than they would have without the effects of climate change.

Wildfires Pollute Air More Than Previously Thought. Are Prescribed Burns the Answer?

Dozens of uncontrolled fires were burning this week in Montana, Nevada, Oregon, and Washington, during what is turning out to be an intense fire season. In fact, U.S. wildfires have consumed more than six million acres of land so far this year, according to the National Interagency Fire Center — well above the average annual acres burned for the past 10 years.

The problem was acute enough that the air in Seattle darkened and caused health problems for some residents, as atmospheric smoke wafted from wildfires burning in the Pacific Northwest and British Columbia, Canada, according to The New York Times.

And all of this is likely a larger public health hazard than previously thought, according to a recent study published in the Journal of Geophysical Research: Atmospheres.

Fires, after all, release harmful pollutants, including what’s known as fine particulate matter, into the air we breathe, which can aggravate or contribute to the development of respiratory and cardiovascular diseases like asthma or chronic obstructive pulmonary disease. Better information on the types of pollution emitted by fires could help officials find ways to reduce the impact of fires on air quality and public health.

According to the authors of the new study, including L. Gregory Huey, an atmospheric chemist at the Georgia Institute of Technology and chair of the institute’s School of Earth and Atmospheric Sciences, wildfires emit three times more of this sort of fine-particle pollution than suggested by similar data compiled by the Environmental Protection Agency.

The emissions data for the new study were collected by several instruments on two research aircraft — a NASA DC-8 and a U.S. Department of Energy Gulfstream-1 — flown over dozens of wildfires and “prescribed burns” during the summer and fall of 2013 in the western, central, and southeastern U.S. Some land managers initiate prescribed burns, also known as controlled burns, as a way to consume wood and other fuel that builds up over time and to cut back on wildfires, which typically are harder to control, as well as more dangerous and smoky.

The analysis, which focused on wildfires in Washington, Oregon, and California, compared the quantities of chemicals and particles emitted per kilogram of fuel burned in the 2013 fires with similar measures for fire emissions by the EPA in 2011. Those figures were converted to annual emissions in both studies, which were comparable given similar areas of burned biomass per year.

The results for fine particles stood out, suggesting that past researchers have significantly underestimated the fine particles emitted by wildfires.

“Particulate matter is a primary pollutant that is clearly impacted by biomass burning,” says Huey. “That is, the more fires you have, the higher the particulate matter. If you want to control particulate matter in your state, you need to know the sources.”

On that front, the newly compiled data suggest that if forest fires are inevitable with the accumulation of forest fuels, intentional, prescribed burns might well be better for public health overall. A given amount of fuel from a prescribed burn, the new study showed, emits less than half of the fine particles by mass than the same amount of wildfire fuel. The finding supports the use of prescribed burns to reduce the effects of fine particles on regional air quality, rather than waiting for imminent wildfires and the filthier air they bring.

Of course, prescribed burns can get out of control, but many land managers say that they are an effective and efficient way to reduce the risk of wildfires, which scientists say have grown and will continue to grow more frequent as the planet warms up. Indeed, while it is difficult to pin any individual weather event partially or entirely on global warming, some trends are clear: The number of wildfires occurring annually in the U.S. has doubled since 1970, according to a 2013 report by Climate Central, a non-profit climate news and research organization. And wildfires are growing larger as the planet’s average temperatures continue to rise, a 2006 study found.

All of this suggests that the use of prescribed burns — a hotly debated issue that has divided communities across the West for some time — might well be presented more frequently in coming years as a means of improving regional air quality, though that’s likely to remain contentious.

“Prescribed burning,” Huey noted, “is also clearly a political issue.”