Local problem, global impact

 

Wildfires that ravaged parts of Indonesia in 1997 spewed out as much carbon dioxide in a few weeks as the entire. Earth can absorb in a full year, new research reveals. Dick Ahlstrom reports.

Catastrophic events affecting small areas can have a global impact according to new research. The Indonesian wildfires which burnt forests and peat bogs in 1997 had a significant affect on the Earth's carbon cycle.

New research into how these fires affected the atmosphere is described today in the journal, Nature.

A combination of an ongoing El Niño and the uncontrolled fires threw up more carbon than the Earth could absorb, although the burning took place in a comparatively small area.

The work was done by Dr Susan Page and colleagues of the University of Leicester in Britain. She calculated that the 1997 fires sent 2.6 billion tonnes of carbon, mostly in the form of carbon dioxide, into the atmosphere. This figure represents more carbon than the biosphere can remove in 12 months in the form of plant growth, oceanic absorption and other carbon sequestering mechanisms.

While the assumption was that most of the carbon dioxide arose from the burning of forests, it was actually Indonesia's extensive peat bogs that produced most of this greenhouse gas volume, the authors note. The peat bogs smouldered for weeks, losing between 25cm and 85cm of their depth while they burned.

In Borneo alone, burning spread across 8,000 square kilometres of swamp forest in Central Kalimantan.

This most likely consumed about 33 per cent of Indonesia's peat bogs overall, the authors say.

While this represents a massive burn area, it is small compared with the Earth's surface, hence the fact that localised events can have an impact beyond their apparent size.

The proof is seen in the fact that the fires caused the largest annual increase in carbon emissions in a single year since records began, the authors state. Because burning bogs can have such an affect means that their preservation is of some importance to the Earth's carbon dioxide equation and global warming, the authors suggest.

"Tropical peatlands are one of the largest near-surface reserves of terrestrial organic carbon and hence their stability has important implications for climate change," they write. "In their natural state, lowland tropical peatlands support a luxuriant growth of peat swamp forest overlaying peat deposits up to 20 metres thick."

Stability goes out the window, however, and this massive carbon source becomes a source of hazard due to "persistent environmental change" the authors say, in particular drainage and forest clearing, practices that make the bogs susceptible to fire.

When fire did strike it occurred during an El Niño-driven dry season that left the bogs in an ideal condition to burn. Strong winds completed the equation and kept the fires smouldering for weeks and sent plumes of smoke across the Pacific. Related studies by others, details of which supported the Leicester findings, showed how the fires affected the gas mix in the atmosphere.

The Leicester team used satellite images of 2.5 million hectares in Central Kalimantan, taken both before and after the fires. The comparative analysis showed more than 30 per cent of the bog surface had burned with peatland accounting for 91.5 per cent of this.

Based on the depth of burn, the team estimated that the peat had released 2.6 billion tonnes of carbon with a further 50 million tonnes of carbon released by the burning of overlying vegetation. This is equivalent to up to 40 per cent of the mean annual global carbon emissions from fossil fuels.

"The extensive fire damage caused in 1997 has accelerated changes already being caused in tropical peatlands by forest clearance and drainage," the authors say.

They studied ongoing logging activities since the fires in 2000 and found that "logging had increased by 44 per cent during this period, thus making the remaining forests more susceptible to fire in the future".

This they stated was a "matter of concern" because undamaged peat swamp forest is essential to maintain high water levels, protect the peat carbon store and facilitate future carbon sequestration from the atmosphere.

All this is put at risk for the future, they warn.

"Tropical peatlands will make a significant contribution to global carbon emissions for some time to come unless major mitigation, restoration and rehabilitation programmes are undertaken," the authors say.

The article on magnetic research has been postponed until next Thursday's Science page