Burning bogs belch carbon

Global-warming models should account for peat in forest fires

nature.com

TOM CLARKE

Indonesia's 1997 fires covered an area twice the size of Belgium

Wildfires in the tropics are spewing carbon dioxide and other greenhouse gases into the atmosphere, a new study finds. They could influence global warming, and look set to get worse.

Fires ravaging parts of Indonesia during the 1997 El Niño-driven dry season pumped as much carbon into the atmosphere as all the living things on the planet remove from it in a year. This is the same as Europe's annual carbon emissions from burning fossil fuel, says ecologist Susan Page of the University of Leicester, UK, who led the study1.

"I was stunned," says David Schimel at the National Center for Atmospheric Research in Boulder, Colorado, recalling how he had to check the calculations for himself.

But another analysis backs up the results. Ray Langenfelds of the Commonwealth Scientific and Industrial Research Organisation in Aspendale, Australia, and colleagues measured trace amounts of other fire-related gases in the atmosphere. They agree that a large part of the pulse of carbon dioxide seen in 1997-1998 came from wildfires - the largest being in Indonesia2.

Wildfires must now be factored into models of global warming, says Schimel. Page's study will help scientists estimate how much carbon a burning bog is putting out, compared with fires in other types of forest.

For peat's sake

The powerful pulse of carbon came largely from smouldering peat swamps, which are up to 20 metres deep in some parts of Indonesia. Peat is compacted plant material preserved in bogs by acid. It is so rich in carbon it can be used as fuel. Most of the burning peat in Indonesia lost 25 to 85 centimetres of its depth.

Page's team worked in the Central Kalimantan province of Borneo, where 8,000 square kilometres of swamp forest burnt. Fires covered about 60,000 square kilometres of Indonesia's peat swamp overall - an area twice the size of Belgium. This constitutes around one-third of the archipelago's total peat swamp.

The release contributed as much as 40% to the largest annual increase in carbon emissions since records began in 1957 says Schimel. Increasing fossil-fuel burning and wildfires in North America and Australia during this extremely dry El Niño year contributed to the total.

Smoke signals

The 1997 El Niño was only part of the reason why normally fireproof bogs turned into tinderboxes. "Peat swamps are under huge development pressure," Page says. Schemes to convert bogs to farms are drying them out by removing trees for timber and drainage.

As Indonesia develops its remaining peat bogs, the situation can only get worse. And bogs like those which burned in 1997 still have life in their embers, because the peat extends so deep. "There's at least another ten fires left in many of them," says Page.

Schimel is in no doubt that human intervention is fanning the flames. "There have probably been El Niños for millions of years and they haven't all burned up."