Estimates of carbon dioxide emissions from wildfires may be significantly overestimated, a recent Oregon State University study indicates.
Earlier studies assumed that nearly a third of live trees were burned when four large fires blazed through central Oregon's Metolius River Watershed in 2002 and 2003. The new study, however, puts the tree bulk consumed at only 1 to 3 percent.
The discrepancy means that estimates of the carbon releases from these fires were too high, the researchers found. According to one earlier figure, just one of these fires released 600 percent more carbon than fossil fuels burned that year in all of Oregon. In comparison, the new study found that the four fires in sum only accounted for about 2.5 percent of the state's total carbon emissions.
"Even though it looks like everything is burning up in forest fires, that simply isn't what happens," Garrett Meigs, an author of the paper, published in the journal Ecosystems, said in a statement. "The trees are not vaporized even during a very intense fire. In a low-severity fire many of them are not even killed."
One reason for the errors, the authors said, is that estimates are based on past studies of Canadian forests, which react differently than U.S. forests.
In general, they said, the climate impacts of forest fires need to be based on more studies that account for different types of forests, soils and fire intensities. And depending on the vegetation and type of fire, some trees and brush may grow back faster than others.
As a result of these problems, overall, the greenhouse gas emissions from U.S. forest fires may be overestimated. The upshot, they warned, is that while the severity and frequency of forest fires may increase due to climate change, there are better ways to prevent climate change than to focus on fire emissions.
Conservation and climate advocates are now pushing for forest protection incentives to be included in both U.S. climate legislation and a global climate pact. But accurately measuring forest carbon emissions and sinks, whether from forest fires or timber harvests, is one major obstacle to implementing these programs.
Another recent study, for example, said that the Intergovernmental Panel on Climate Change's 2007 estimate of tropical deforestation-related emissions was also overstated and based on old information. The widely cited figure -- linking deforestation to nearly 20 percent of human-caused carbon dioxide emissions -- should be closer to 12 percent, the Nature Geoscience study found.