THE VINE MARCH 18, 2010
In recent years, climate scientists have started paying a lot more attention to the role of forest fires. Everyone understands how fires can contribute to global warming: Trees suck up and sequester CO2 as they grow, and they release all that carbon back into the atmosphere when they burn up. But how big an impact do these fires have? Quite a bit: Last April, a major study in Science estimated that as much as 20 percent of the carbon-dioxide that humans have put in the air since industrialization has come from deforestation fires—people intentionally setting forests ablaze to clear land for farms or development. (Slash-and-burn agriculture is still rampant in places like the Amazon.)
That's intentional deforestation. But what about accidental wildfires? Turns out, those are a big deal, too. Back in 2007, researchers at the National Center for Atmospheric Research (NCAR) in Boulder used satellite observations to estimate that large-scale fires in the United States pump out about 290 million tons of CO2 each year—equal to about 6 percent of the emissions caused by fossil fuel use. Worse, as the planet keeps heating up, those wildfires are expected to become more frequent—partly because the hotter, drier temperatures make forests more flammable, and partly because the warmer climes are leading to bark beetle infestations, which chomp through forests and turn them into kindling. It's a vicious cycle.
In any case, NCAR has just put out yet another study on the subject that has a more positive spin. As it turns out, many of those large-scale wildfires could be avoided or contained through the use of "prescribed burns." If land managers periodically set smaller, controlled fires that cleared away the underbrush in the forests, they could reduce the chances of bigger fires breaking out and protect the bigger trees. (By contrast, land managers in the West have frequently taken to suppressing fires altogether, which has led to extremely dense forests that are, unfortunately, very vulnerable to big wildfire outbreaks—especially as temperatures rise.) Here's the key finding:
The results showed that carbon emissions were reduced by anywhere from 37 to 63 percent for the forests that had been subject to prescribed burns, depending on the vegetation mix and location of the forests. Overall, carbon emissions for the 11 Western states were reduced by an annual average of 14 million metric tons. That is the equivalent of about 0.25 percent of annual U.S. carbon dioxide emissions, or slightly more than the annual carbon dioxide emissions from all fossil fuel sources in some less-populated states, such as Rhode Island or South Dakota.
That's a pretty significant improvement, even if it's not going to solve all our carbon woes. Though these prescribed fires could also help slow down that pesky warming/beetle/wildfire feedback loop that we're already starting to see out West.