Smouldering peat fires across Indonesian Borneo are releasing ancient stores of carbon into the atmosphere and generating a toxic cross-border haze affecting Singapore, Malaysia, Brunei, the Philippines, and Indonesia. The fires, supercharged by severe drought conditions driven by a Super El Niño, have carbonised some 200,000 hectares of forest and farmland since early July.
## Transnational Haze and Public Health Impacts
The resulting smog has blanketed major urban centers across South East Asia, driving air pollution indices to extreme levels. In some areas, pollution has reached almost 75 times the World Health Organization’s recommended level.
The human toll has climbed steadily as populations breathe in the dense, amber-hued smoke. Between July and August, Indonesia’s Health Ministry recorded over 50,000 cases of respiratory infections linked to land and forest fires. Among those patients, more than 12,000 were children under the age of five.
“Everybody who’s living within that pollution cloud is breathing in the products of those smouldering peat fires,” said Susan Page, a professor at the University of Leicester’s school of geology and the environment who has been researching peatlands in Asia for three decades. “They’re breathing in carbon monoxide, which is toxic.”
Volunteer firefighters operating in the haze report severe physical strain from the conditions. Dwi Sujatmoko, a 35-year-old volunteer, described the environment as resembling tear gas.
“It hits your nose straight away, your eyes burn—that’s more or less what it’s like,” Sujatmoko said, adding that he has spent more than a month working against persistent fire fronts. “People say these fires are extraordinary because of the flames and the smoke. And they’re right.”
Operating with hand tools, carts, and portable fire pumps, volunteer crews—many of them indigenous Dayak or Banjar people—are struggling to contain blazes that burn both above ground and below the surface.
“Once a fire becomes uncontrolled, it harms many people. Not just humans, but also animals and plants,” Sujatmoko said. “If underground fire spreads and can no longer be controlled, the losses are enormous.”
## The Mechanics of a Subterranean Carbon Bomb
Unlike standard surface wildfires, Borneo’s current crisis is concentrated in a 4.5-million-hectare tropical peatland ecosystem. Under normal environmental conditions, these waterlogged swamps slow the rate of organic decomposition, enabling carbon to accumulate underground for thousands of years.
When these ecosystems are drained or burned, however, they transform into major greenhouse gas sources.
“Peatlands are incredibly effective carbon stores because their waterlogged conditions slow decomposition, allowing carbon to accumulate underground for thousands of years,” said Dr Nisa Novita, a peatland researcher at the Indonesian conservation NGO Yayasan Konservasi Alam Nusantara (YKAN). “But this also means they can become a ‘carbon bomb’ when they are drained or burned, because that carbon can be rapidly released into the atmosphere.”
According to Dr Nisa, peat deposits in Kalimantan can exceed 20 metres in depth. A deposit of that scale has been known to harbour more than 6,000 tonnes of carbon per hectare—an amount roughly equivalent to the annual CO₂ emissions of 4,800 cars. When these deep layers catch fire, they release pulses of carbon dioxide, carbon monoxide, and methane out of sight beneath the soil.
With thousands of active fire hotspots multiplying across Indonesia under extreme drought conditions, the immediate firefighting effort remains focused on containing subterranean fronts that continue to smoulder.
