Aug. 7, 2009 -- As the climate gets warmer and dryer, forest fires will become as much as three times more common in parts of the American West. As a result, air quality will suffer, and so will our ability to breathe, found a new study.
This was the first study to look at just how bad the air is going to get as wildfires rage into the future. As the nation struggles to tackle other assaults on the atmosphere, the new research emphasizes the need to focus on preventing flames, too.
"The EPA sets standards for what comes out of the tail of a car or a power plant," said Jennifer Logan, an atmospheric chemist at Harvard University in Cambridge, Mass. "You can't control what comes out of a forest fire once it starts."
Even as forest fires seem to be appearing more often in media reports, scientists only began documenting the extent of the trend in the last few years. Records now show that, in the western United States, the amount of area burned annually by fires was more than six times higher between 1987 and 2003 than it was between 1970 and 1986.
Increases have also been documented in Canada and Alaska.
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Scientists know that burning wood and underbrush spews gasses and particles into the air that are pushed around by winds. Those particles can irritate lungs but are especially dangerous to people who have trouble breathing as a result of asthma and other chronic conditions.
Figuring out just how much pollution a fire emits, however, is complicated. The relationship depends on the types of wood involved, how hot the air is, how much fuel is lying around on the ground and more.
The researchers looked at 25 years' worth of fire records to first quantify how big a fire will become given weather-based factors like temperature and humidity. Using standard climate models to project the future, they estimated that by the 2050s, fires could burn 80 percent more area in the Pacific Northwest.
In the Rocky Mountains, fires could burn 175 percent more land, they reported in the Journal of Geophysical Research. Overall, an average of 50 percent more area could burn across the American West.
From there, the researchers created another computer model that combined future fire projections with previous calculations linking fires with the amount of carbon emissions they produced. The model estimated a 40 percent rise in lung-irritating carbon aerosols by the 2050s.
"Going into this, we expected to see an increase in forest fires simply because temperatures are going to be warmer 40 or 50 years from now," Logan said. "We didn't know how big it was going to be and we didn't know what affect it was going to have on air quality."
The results are convincing but not guaranteed, said Gabriele Pfister, an atmospheric scientist at the National Center for Atmospheric Research in Boulder, Colo. If people start using land in different ways or if the types of trees change, among other factors, the future could play out differently, for better or worse.
Human interventions could make a positive difference. Clearing forests of underbrush and conducting controlled burns can help reduce the risk of fires.
Forest fires are natural events, Pfister added, with an important role in ecosystems. It's our own behavior that we should be concerned about.
"We have to be aware that because of our impact on the environment, we are having an impact on these fires as well," she said. "If they get worse, they're not natural anymore."
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