From Scientific American:
According to a landmark report that will be published tomorrow in Science, fires are not just a result of a changing climate, they're also contributing to the overall warming trend much more than imagined, the authors report. As vegetation burns, it releases stored-up carbon into the atmosphere, speeding global warming and thereby exacerbating conditions that may generate a greater incidence of wildfires in the coming years.
Because fires have been part of the global environment for hundreds of millions of years—since the first land plants emerged—as well as a tool for humans for more than 50,000 years, they're largely assumed to be a natural and negligible part of the carbon and climactic cycles. As people use fire on a massive scale as a cheap and efficient way to clear forests for agriculture or development, however, it is having a much greater impact than many scientists realized. In fact, deforestation fires alone have contributed 20 percent of the total greenhouse gases humans have contributed to the atmosphere since industrialization.
The report brought together 22 scientists from a range of disciplines and countries in an effort to better understand the global impact of fire. "This is a critical move away from the thinking that fires are just a disaster," says David Bowman, a professor of forest ecology at the University of Tasmania in Hobart, Australia, and a lead author of the report. Taken in isolation, each conflagration can cause massive human, economic and natural devastation, but as a broader force fire wields a much larger power, according to the report. "Fire is a feature of our planet…. High levels of fire activity have the capacity to change climate," he says.