Feb. 25, 2009 -- Two of the most destructive consequences of climate change -- drought and wildfires -- may have an upside.
Over the course of many centuries, they conspire to suck greenhouse gases out of the atmosphere, according to a new study.
Wildfires scorch portions of the United States every year, from the lodgepole pines of Colorado to the dry, sunbaked brush of southern California. They spew huge amounts of carbon dioxide into the atmosphere, equivalent to as much as 4 percent of the country's total industrial emissions.
If western United States becomes increasingly parched due to climate change, as climate models predict, the risk of wildfire will become ever greater.
In the long run, that may not be such a bad thing. An analysis of 2,000 years of sediment deposits from the bottom of the Chesapeake Bay reveals that droughts coincide with more wildfire activity. They also produce tons of carbon-rich soot and charcoal that gets buried in soil or underwater sediments.
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The connection between drought and wildfire is strongest over the last millennium, starting with a stretch of planet-wide warming called the Medieval Warm Period, around 700-1100 A.D. Eastern North America dried out during this time, and black carbon deposits spike dramatically in the Chesapeake Bay sediments.
"We're not sure how big the fires were," Siddhartha Mitra of East Carolina University, the lead author of the study said. "But the amount of black carbon we see suggests they were pretty darn large."
Though the team hasn't made a formal calculation, Mitra said that as much as 30 percent of all the carbon locked up in trees, grasses and other plant matter that burns may be sequestered.
The finding could have implications for climate policy in the future. There may be a way to burn large swaths of forest or grassland as a means of carbon sequestration.
"There's a trade-off, a balance between the net loss of carbon to the atmosphere versus the net gain in carbon from sequestration," Mitra said. "When do you get to the break even point? Does burning benefit us to some extent that we haven't thought of before? These are the kinds of questions we need to be asking."
But Jason Neff of the University of Colorado, Boulder argues the potential to dampen the effect of global warming is remote.
"It's not enough to let any of us sleep easier at night," he said. "The amount of carbon sequestered is probably a fraction of 1 percent of human emissions."
What's more, it will be be a century or longer before the benefits of sequestration take over. On shorter time scale, carbon emissions from fires are likely to make matters worse.
"There's a big debate about how far you go managing natural systems to maximize carbon acquisition, and minimize carbon loss," Neff said. "We need to be cautious how we proceed."
Related Links:
HowStuffWorks.com: How Carbon Capture Works
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