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Aerial view of forest fire
Photo: Ian MacPherson, National Research Council of Canada

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An Environmental One-two Punch?

One of the anticipated effects of climate change is to make droughts more common and widespread. More droughts will mean more forest fires. More forest fires will dump thousands of tonnes more carbon dioxide, a greenhouse gas, into the atmosphere. This kind of a dangerous chain reaction has been suggested research conducted by the National Center for Atmospheric Research (NCAR).

"We're using the western U.S. as a case study area where climate and land use are interacting in several interesting ways," says NCAR senior scientist David Schimel. "Land disturbance is a fundamental factor shaping ecosystems."

The researchers developed a new computer model of a complex forest ecosystem to simulate the release of carbon during the 2002 fire season in Colorado. The findings estimate how much carbon would be stored in a normal year compared to a drought year, such as 2002. More carbon is freed from storage during droughts, not only because more tinder-dry vegetation burns, but because plants deprived of water grow more slowly, absorbing and storing less carbon in their tissues.

The conclusion from these early studies is that the fires have had a significant effect on the regional carbon balance, changing Colorado from a storage area to a source of atmospheric carbon. And, since carbon circulates globally, the Colorado fires even had a very small effect on the global carbon budget.

Computer models have been used before to estimate how much carbon dioxide is circulating in the atmosphere, how much is stored as carbon in vegetation and soils, and how much is shifting between land storage and the atmosphere. However, "it's much harder to take the system apart than early modeling efforts suggested," says Schimel.

The current project incorporates land use, drought, soil health, and other factors to better capture the complexity of ecosystem interactions at the local level.

Projections of climate change in the West include hotter temperatures and increased drought, a recipe for more forest fires. If further research supports the project's early findings, "We're either going to be spending a lot more money on fire suppression or we're going to be seeing a lot more carbon released by wildfires," Schimel says.