Wildfires in the lowlands of southeast Asia can have a major impact on global warming. That's the conclusion of a study published in the scientific journal Nature. A single wildfire in Indonesia spewed billions of tons of carbon dioxide, a greenhouse gas, into the earth's atmosphere.

In 1997, during a severe drought sparked by a climate phenomenon known as El Nino, a wildfire burned in central Kalimantan. But it was not the kind of wildfire that scorched dried timber and brush and moved on. This fire smoldered on the Indonesian part of the island of Borneo for months in rich forest bedding known as peat (PEET) lands.

"We're talking about an environment which is water-logged for most of the year, and which usually has very deep organic soils, peat soils, which are usually quite acidic and very low in plant nutrients," she says Susan Page, a peatland ecologist at the University of Leicester in England.

Professor Page said 70 percent of the world's tropical peatlands are in southeast Asia, mostly in Indonesia and Malaysia. She said when the normally moist forest floor becomes stressed by logging and drought, it becomes dry on top and wet one or two meters below the surface.

This, she said, is a recipe for smoldering that lasts weeks or months on end, producing lots of particulate matter or soot that rises into the atmosphere.

Using satellite imagery, Professor Page and colleagues determined that a huge amount of carbon dioxide, the primary greenhouse gas, was emitted. "We've come up with a range for values of carbon emissions into the atmosphere which is somewhere between one and 2.5 billion tons of carbon from that single fire event," she said.

Professor Page said the amount of carbon belched into the atmosphere from the Kalimantan fires is significant on a global scale. "Because even if we took the lower end of the range and looked at something like a billion tons, that would equate to a sixth of all the world's carbon emissions from the burning of fossil fuels, such as coal, oil and other fossil derivatives," she explained.

Professor Page said that's about as much carbon dioxide as is removed naturally from the earth's biosphere each year.

David Schimel is a senior scientist with the National Center for Atmospheric Research in Boulder, Colorado. In a commentary in Nature, Mr. Schimel explains that under normal conditions, the moisture of the forest floor would have kept the wild fires sparked by el Nino to a minimum.

"What happened with forest clearing there is that the roads and other sorts of channels that were cut back in the forest to dry out and it allowed the water table to drop. And, so, instead of staying wet like a sponge through the entire drought, the forest dried out and became susceptible to these very extensive fires. I think one comparison is these fires covered twice the size of Belgium. So, in a normal year, they would cover just a few square miles (kilometers)," he said.

Unless countries alter their land management practices by curbing the widespread clear cutting of trees, Mr. Schimel worries that peatland fires, such as what happened in Indonesia will be a continuing problem.