Wildfires dominated the western parts of the United States earlier this year and established 2002 as the most expensive fire year yet. But the consequences of burning land and brush are more than just financially costly. Study results published today in the journal Nature suggest that wildfires can have a huge impact on the amount of greenhouse gases, particularly carbon dioxide, in the atmosphere. Specifically, scientists found that fires in Indonesia during 1997 spewed the same amount of carbon into the air as is typically removed annually by the entire planet's biosphere.

Susan E. Page of the University of Leicester and her colleagues used satellite images of a 2.5-million-hectare region of Borneo taken before and after the fires to assess their effects. The team found that 32 percent of the overall area had burned and that most of the land affected was comprised of peat bogs. Because peatland is so effective at storing terrestrial carbon, the fire's pattern had a significant effect on the global carbon budget. (The image above was taken on September 27, 1997 and shows smoke blanketing Lake Toba, Indonesia.) By extrapolating their findings to the country as a whole, the scientists determined that between 0.8 billion and 2.6 billion tons of carbon was released into the atmosphere by the fires. That amount is equivalent to 13 to 40 percent of the annual emissions from burning fossil fuels, making the fires significant contributors to the largest jump in atmospheric carbon dioxide levels since recordkeeping began in 1957. As David Schimel and David Baker of the National Center for Atmospheric Research in Boulder, Colo., point out in an accompanying commentary, "catastrophic events affecting small areas can evidently have a huge impact on the global carbon balance."