Conflagrations in forests growing on tropical peat can produce up to one-third as much carbon dioxide as all fossil fuel burning in some years, two new studies show. Forest clearance for agriculture is the spark for these fires, and curbing the practice could help reduce global warming.
A 1997 fire in Indonesia incinerated roughly 60,000 square kilometers, destroying not just trees, but the carbon-rich peat underneath. The peat, a product of decaying organic matter, is up to 20 meters thick in places. Local farmers and large companies commonly drain and burn these peatlands to plant crops. That, combined with droughts from El Niño, enables small fires to burn out of control and release unknown amounts of carbon dioxide, the main cause of global warming.
To determine the amount of carbon dioxide released by the 1997 fire, researchers studied 25,000 square kilometers on the island of Borneo. Because of inaccessible terrain, they used satellite images to measure the area and thickness of peat and the extent of forests and farms. Ground and aerial observations in some areas verified these measurements. Around 8000 square kilometers of the study area burned in 1997, 92% of it covered by peat, ecologist Susan Page and colleagues at the University of Leicester, U.K., report in the 7 November issue of Nature.
Extrapolating to the rest of Indonesia suggests that the fires released about 2 billion tons of carbon dioxide, roughly a third of the carbon dioxide released by human activity that year. The team estimates that about 80% of the Indonesian emissions came from peat, the rest from vegetation. Page says that humans clearly cause the larger fires that burn more peat. "Drought is not a new phenomenon in Indonesia, but forest fire--and in particular fire in the peat swamp forests--is."
The findings jibe well with another recent study that estimated the carbon dioxide released by fires from the ratio of trace gases in the atmosphere. The tight match suggests that the new work is "well inside the ballpark," says atmospheric scientist David Schimel of the National Center for Atmospheric Research in Boulder, Colorado, who is not associated with either study. Schimel says Page's results are surprising but solid. "I did not believe it until ... I checked against the atmospheric data," he says.