Wildfires across Indonesian Borneo have torched some 200,000 hectares since early July, sending smoke across Southeast Asia and burning into peat deposits that hold carbon accumulated over thousands of years. The fires have produced air pollution levels reaching almost 75 times the World Health Organization’s recommended level in some cases, while Indonesia’s Health Ministry recorded over 50,000 respiratory infections linked to land and forest fires between July and August.
More than 12,000 of those cases involved children under the age of five. The haze has spread to Singapore, Manila and Kuala Lumpur, as well as Malaysian Borneo. ASEAN has activated a Level 3 transboundary haze alert, its highest, for the southern part of the region. The crisis is the region’s worst in more than a decade.
The current estimate of land burned is about 200,000 hectares, although the precise extent remains unclear. Different sources have cited 200,000 hectares, 300,000 hectares and 110,000 hectares. The timetable for containing the fires is also unknown, with sustained rainfall needed to help suppression efforts.
Borneo contains one of the world’s largest tropical peatland ecosystems. Its 4.5-million-hectare swathe of peatland forest and swamp is a reservoir for ancient carbon under normal conditions. A peatland can harbour more than 6,000 tonnes of carbon per hectare, roughly equivalent to the annual CO₂ emissions of 4,800 cars. Peat deposits in Kalimantan have been found to exceed 20 metres in depth.
Peatlands are waterlogged environments formed from thick layers of partially decayed plant material. When they are drained for development, the exposed material becomes far more vulnerable to fire. Drained peatlands continuously emit carbon dioxide into the atmosphere, whether they are burning or not.
Once ignited, peat can smoulder below ground for weeks or months, including when surface conditions appear wet. Massive underground fires persist beneath the surface and release toxic fumes into the atmosphere. Peatlands also release millions of tonnes of carbon dioxide, carbon monoxide and methane when they catch fire.
Volunteer firefighters are using hand tools, carts and portable fire pumps to tackle the blazes. Government task forces have mobilised across multiple Indonesian provinces. Cloudseeding and firefighting aircraft have been deployed across five provinces, though their effectiveness remains unknown.
The fires are largely man-made, with blazes deliberately set by individuals or companies clearing land for agriculture or other economic activity. The clearing has been associated with palm oil, agriculture, pulp and paper. The crisis also reflects decades of land-use change dating to the Suharto era, when extensive tracts of rainforest peat in Kalimantan were cleared for logging, plantations and large-scale development.
Those development initiatives have primarily drained peat swamps, increasing their susceptibility to fire. An intensifying El Niño weather pattern has dried soils faster than in previous El Niño years, according to the brief. Hotspot rates are higher than in previous El Niño years, including 2015, 2019 and 2023.
The fires threaten to activate what are described as “carbon bombs”, huge reservoirs of carbon beneath Indonesia’s peatlands that are thousands of years old. Indonesia generated 46 megatonnes of carbon from August to September, its highest level since 2003. Fires released more than 23 million metric tons of carbon between 28 August and 3 September.
The potential scale has a historical precedent. A study of Indonesia’s 1997 fires, published in the journal Nature, found that peat and vegetation combustion released between 0.81 and 2.57 gigatonnes of carbon. That was equivalent to between 13 and 40 per cent of the world’s total annual emissions from burning fossil fuels. Drained and burned peatlands account for up to 5 per cent of all human-caused carbon emissions worldwide, according to the United Nations Environment Programme.
The present fires’ eventual emissions, economic cost and effect on long-term peatland restoration remain unclear. The 2015 fires cost $16.1 billion and affected 43 million people, according to the brief. It is also unknown whether the current emissions trajectory will match or exceed 2015 levels by the end of the fire season.
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