Image source, Ahmad Dhani for BBC Image caption, Fahrin Ramadhianto has been fighting Borneo's wildfires for a month - and noticing the impacts on his body.
ByGavin Butler and Ahmad Dhani, Reporting fromBanjarbaru, Kalimantan Published 2 hours ago The sky grows heavy in Borneo, though not with rain.
The air, amber-hued and treacle-thick, is smudged under a blanket of smog that has spilled across international borders – to Singapore, Manila, Kuala Lumpur.
Down on the ground, smoke steams from the soil.
It's like tear gas, says Dwi Sujatmoko.
"It hits your nose straight away, your eyes burn – that's more or less what it's like," he says.
"People say these fires are extraordinary because of the flames and the smoke.
And they're right." The 35-year-old volunteer firefighter has spent more than a month enveloped in this haze, breathing toxic millennia-old microparticles of carbon as he toils against a seemingly inextinguishable fire front.
Using hand tools, carts and portable fire pumps, he and thousands of other volunteer firefighters – many of them indigenous Dayak or Banjar people – are up against an inferno that has carbonised some 200,000 hectares of forest and farmland across Indonesian Borneo since early July.
Underground and out of sight, giant subterranean peat fires continue to smoulder, choking the air with poisonous fumes.
"Once a fire becomes uncontrolled, it harms many people.
Not just humans, but also animals and plants," Sujatmoko says.
"If underground fire spreads and can no longer be controlled, the losses are enormous." Image source, Ahmad Dhani for BBC Image caption, Fires have torched some 200,000 hectares across Indonesian Borneo since early July Indonesia is in the throes of a wildfire catastrophe.
Amid a so-called "Super El Niño" that has supercharged local drought conditions, thousands of active fire hotspots are spreading and multiplying across the country, fuelling a transnational haze crisis that is the region's worst in more than a decade.
But what makes Borneo's fires particularly worrying is the fact that they are burning through one of the world's largest tropical peatland ecosystems.
This 4.5-million-hectare swathe of forest and swamp, under normal conditions, serves as a valuable reservoir for ancient carbon.
When these peatlands catch fire, they risk releasing millions of tonnes of carbon dioxide, carbon monoxide and methane into the atmosphere – a "pulse" of greenhouse gas emissions that has earned them the sobriquet of "carbon bomb".
"Peatlands are incredibly effective carbon stores because their waterlogged conditions slow decomposition, allowing carbon to accumulate underground for thousands of years," explains Dr Nisa Novita, a peatland researcher at 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.
"Tropical peatlands in Indonesia are among the world's most effective natural carbon stores.
The deeper the peat, the greater the carbon stock – and in Kalimantan, we have found peat deposits that can exceed 20 metres in depth." A peatland that deep has been known to harbour more than 6,000 tonnes of carbon – roughly equivalent to the annual CO₂ emissions of 4,800 cars – per hectare.
And when it burns, says Dr Nisa, that fossilised carbon can be released into the atmosphere "very rapidly".
Image source, Ahmad Dhani for BBC Image caption, "We're doing everything we can to help deal with this haze disaster because it's our duty," says firefighter Dwi Sujatmoko The toxic cloud Thousands of people across South East Asia are now feeling the effects of those emissions in their eyes, chests and throats.
Across Indonesia as well as Brunei, Malaysia, Singapore and the Philippines, air pollution indices have soared to "unhealthy" extremes - almost 75 times the World Health Organization's recommended level, in some cases – and hospital admissions have surged.
Between July and August, Indonesia's Health Ministry recorded over 50,000 cases of respiratory infections linked to land and forest fires.
More than 12,000 of them 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," says Susan Page, a professor at the University of Leicester's school of geology and the environment, who's been researching peatlands in Asia for three decades.
"They're breathing in carbon monoxide, which is toxic, and they're breathing in the very finely divided particulate matter... [which] can pass through the alveoli in the lungs into the bloodstream and cause further problems elsewhere in the body, including issues with the heart.
"Living in this kind of pollution cloud is extremely unhealthy." Image source, Ahmad Dhani for BBC Image caption, Fighting peat fires requires saturating the ground so thoroughly that it becomes "like porridge" Nowhere are these health impacts being felt more acutely than at the coalface of the disaster: the fire front.
Here, volunteer firefighters have been risking their lives and lungs to extinguish burning peatlands which are notoriously difficult to put out.
Two volunteers in Central Kalimantan have died in recent days, reportedly after their health deteriorated from putting out fires.
Cloaked in toxic haze that can burn years off a person's lifespan, volunteers have been digging ponds, canals and borewells through bone-dry peat in a desperate attempt to keep their hoses tapped.
Some have been driving pipes into the earth, making ad hoc irrigation systems to combat subterranean fires.
Others have been sleeping within a stone's throw of the frontline so they can battle the blazes through the night.
"The worst thing here has been the smoke," says Fahrin Ramadhianto, a volunteer firefighter in South Kalimantan's Banjarbaru, one of the worst-hit areas.
"The smell is like decaying wood being burned – that's the characteristic smell of peat.
And that peat contains decomposed wood and organic material from many different sources." An unnatural imbalance Indonesia's peatland fires are not a new phenomenon.
Experts say the crisis is rooted in decades of land-use change, dating back to the Suharto era, when vast areas of rainforest and peatland in Kalimantan were opened for logging, plantations and large-scale development projects.
Yet authorities have historically avoided blaming industrial actors for causing large-scale fires.
Instead, the same indigenous communities who are now engaged in firefighting operations across the island have often been accused of triggering the blazes, due to traditional farming methods that use controlled burns to clear away vegetation.
Tono, a representative of the Dayak Kanayatn people of West Kalimantan, told the BBC that Dayak communities are frequently used as scapegoats, despite carrying out land clearing with extensive planning, caution and adherence to multi-generational customs.
Tono says these communities' traditional practices, known as uma bukit or "hill farming", are rooted in the idea of maintaining balance with nature.
Image source, Ahmad Dhani for BBC Image caption, "The worst thing here has been the smoke," says Fahrin Ramadhianto But the natural balance is fast unravelling in Kalimantan, the most deforested area in Indonesia.
The region lost almost 160,000 hectares of forest area in 2025, more than one-third of the nationwide figure – much of it to make way for plantations and monocrop agriculture.
It is these same industrial-scale development projects that have been largely responsible for draining the area's peat swamps, which renders them significantly more fire-prone, Prof Page says.
"Peatlands aren't really the ideal place to set up a plantation – but of course, once the more suitable mineral soils had been exhausted it became possible, by using large machinery, to drain the peatlands and create conditions which would be dry enough," she says.
"So not only have you got the deforestation, but peatland drainage of course has also greatly increased the fire risk." Page also points out that, whether on fire or not, a drained peatland emits carbon dioxide into the atmosphere "all of the time".
"I think that's forgotten," she says.
"I think it's important to recognise that when we see the fires, they're like a dramatic example of what is actually going on the whole time in a drained peatland...
The fires are just the worst expression of [that]." Now, as these latest fires continue to spiral out of control, Sujatmoko and others face a concatenation of difficulties in the coming days, weeks and months – not least of which is a shortage of water.
Image source, Ahmad Dhani for BBC Image caption, Drainage and drought in Indonesia's peatlands has exacerbated their vulnerability to fire Fighting peat fires requires saturating the ground so thoroughly that it becomes "like porridge", Sujatmoko explains.
Even then there is a high chance the fire will reappear, like a smoking revenant, fed by hidden fuel buried in the invisible depths of the peat swamp.
In the face of these persistent reignitions, ongoing drought conditions and toxic smog, fatigue is another concern.
"We're definitely tired," says Sujatmoko.
"We get exhausted, we miss our families, our children, our wives.
But for now, all of us are putting those things aside.
We're doing everything we can to help deal with this haze disaster because it's our duty." "We also hope rain comes soon," he adds.
"We've spent months away from home...
May all the efforts of those on the front lines be a blessing for everyone." Additional reporting by Faisal Irfani from BBC Indonesian.
