By Paul Rincon
BBC News science reporter
The destruction of tropical peatlands is contributing significantly to global warming, according to a study.
The fires can rage out of control during dry periods
Peatlands in South-East Asia are being burnt in fires started with the intention to clear forest, but in dry periods they can rage out of control.
This can free vast amounts of carbon dioxide into the atmosphere, Dr Susan Page of Leicester University, UK, said.
The peatlands, which contain up to 21% of global land-based stores of carbon, could be destroyed by 2040, she added.
It has been calculated that in 1997, 2.67 billion tonnes of the greenhouse gas carbon dioxide were released through burning of these peatlands. This is equivalent to 40% of one year's global fossil fuel combustion, Dr Page says.
That year was unusually high, however; the intermediate estimate is one billion tonnes, about 15% of fossil fuel combustion for a year.
Tropical peatlands are spread across numerous islands in South-East Asia, including Borneo, Sumatra and Papua. The peat is found in lowland areas, can exceed 10m in thickness and has a high carbon content of about 60%.
Dr Page regards them as a "Cinderella ecosystem"; their character and importance largely ignored by scientists, politicians and planners.
The importance of the peatlands is largely ignored, says Dr Page
The driving forces behind destruction of the peatlands have included clearance and drainage on a large-scale to set up timber, oil palm or rice plantations, and on a small-scale for subsistence farming and settlement. Poor forest management is also a cause.
"Where you've got large-scale drainage of the peatland and clearance of the forest, the peat is far more susceptible to igniting. If you get fire escaping from plantation clearance or from farming activities the surrounding landscape is far more fire prone," Dr Page told the BBC News website.
On Kalimantan, the Indonesian part of Borneo, a one-million-hectare area was drained and cleared for rice cultivation, devastating the peatlands contained within it.
The failed Mega Rice project under former Indonesian President Suharto's rule was designed to create an enormous region devoted to rice cultivation. But it has since been found that the soils are unsuitable for growing the cereal crop.
Although there has been some success in tackling deliberate fires, natural events are exacerbating the problem. The cleared and desiccated peatland is easily ignited during droughts, which occur every three to seven years during El Niņo events (the last was in 2002).
Clearance and drainage only makes the land more prone to fire
Droughts can also make peat more susceptible to erosion during the rainy season.
Dr Page said she was currently involved in a project to "re-wet" the peatlands in order to restore the water table.
Without this urgent action, together with a fire control programme, the problem was only going to get worse, she added.
Details of the research have been presented to the annual conference of the Royal Geographical Society (RGS).