SAN FRANCISCO, California, December 9, 2002 (ENS) - Wildfires contribute tons of carbon dioxide to the atmosphere, increasing global warming as part of an accelerating cycle, U.S. researchers said this weekend. The fires take carbon out of storage in vegetation and soils, and feed it into the atmosphere as carbon dioxide, a greenhouse gas. Drought makes the problem worse by stunting tree growth and turning forests into dry tinderboxes, and environmental disturbances caused by human activities further reduce the ability of forests to store carbon.
These are some of the preliminary findings from computer modeling studies of the 2002 Colorado wildfires, conducted by a team of researchers from Colorado State University, the U.S. Geological Survey (USGS), and the National Center for Atmospheric Research (NCAR). Their results were at the annual meeting of the American Geophysical Union (AGU) in San Francisco.
"We're using the western U.S. as a case study area where climate and land use are interacting in several interesting ways," said NCAR senior scientist David Schimel. Western lands, particularly evergreen forests, represent about half of all U.S. carbon storage, he said.
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 dry vegetation burns, but also because plants deprived of water grow slower, absorbing and storing less carbon in their tissues.
The team's preliminary conclusion is that the fires have impacted the regional carbon balance, changing Colorado from a storage area to a source of atmospheric carbon. Because carbon circulates around the world, the Colorado fires have also had a small effect on the global carbon budget.
The team is also using computer models to compare different approaches to reducing wildland fire risk. "We don't know which method takes more carbon out of storage, mechanical thinning or prescribed burning, but that's one of the questions we're looking at," Schimel said. "Land disturbance is a fundamental factor shaping ecosystems."
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. But "it's much harder to take the system apart than early modeling efforts suggested," said Schimel.
For example, increasing road density in the West has been linked to increasing wildfires. Roads bring in more people who may ignite fires, and clearcutting and road building channel away water once held in place by the living forest floor, causing a drop in the water table.
Projections of climate change in the western U.S. 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 concluded.:
