The fire under Borneo
Forest and peatland fires on the world’s third-largest island are set by people, stretched by El Niño, and carried as smoke into lungs, classrooms and the last strongholds of the orangutan.
In the last days of August 2026, a mother in Kuching described an island she could no longer see. “The air here is very thick,” Mia Emylia Hassan told Al Jazeera. “It smells like smoke, and it’s just white all over.” Visibility from her house had fallen to about a kilometre. “We have not seen blue sky for over a month.” Her ten-month-old daughter had come home from hospital with a lung infection just as the haze arrived. Twice, the family rushed the infant back because she could not breathe.
The smoke had crossed from fires in Kalimantan, the Indonesian side of Borneo, onto Sarawak. Six areas there recorded hazardous air, above 300 on Malaysia’s Air Pollutant Index. Kuching hit 407. Serian, near the border, hit 408. Palangka Raya reached 780 on the index published by IQAir, and Pontianak reached 593. Deputy health minister Dante Saksono Harbuwono said some 13,500 people were treated for respiratory infections in July and August, and about 5.5 million people on Borneo and Sumatra had been exposed. In one week of late August, Malaysia recorded asthma cases rising from 219 to 1,811, and conjunctivitis from 146 to 720. Nearly 600 schools around Kuching closed, affecting some 200,000 students. Sarawak cancelled outdoor Independence Day celebrations. Al Jazeera called it the worst episode since 2015, when Indonesian fires sickened more than 500,000 people.
Causes
A swamp drained, then set alight
The BBC, explaining the 2019 haze, wrote that burning usually peaks from July to October, when farmers clear vegetation for palm oil, pulp and paper by slash-and-burn and the flames run into protected forest. Slash-and-burn is illegal. Greenpeace International has said some companies appeared “to operate outside the law for years with little sanction.” In 2026, Al Jazeera reported, police arrested 72 people suspected of lighting fires. Analysts told the network the burning was largely deliberate, by companies and smallholders, to open rainforest and peat.
Peat is what makes the fire last. Undisturbed swamp is naturally fire-resistant, Mark Harrison of the Orangutan Tropical Peatland Project told The Guardian in October 2015, because the ground is flooded. Canals and clearance drained it. “Dry peat ignites very easily and can burn for days or weeks, even smouldering underground and re-emerging away from the initial source,” geographer Susan Page told the same paper. Scientific American traced one canal system to 1996, when President Suharto’s Mega Rice Project tried to turn one million hectares of Bornean peat into paddies. No rice was harvested. The canals kept draining the swamp. Louis Verchot, of the Center for International Forestry Research, called the dried peat “forest cemeteries,” and Page said severe fires did not occur before that kind of development. Helena Varkkey, at Universiti Malaya, told Al Jazeera that a strengthening El Niño means hotter, drier weather, so “any fires that happen will have a bigger and longer regional impact.”
“Dry peat ignites very easily and can burn for days or weeks, even smouldering underground and re-emerging away from the initial source.”
Duration
How long the island burns
A peat fire is not finished when the flame goes out. Atmospheric scientist Jayaprakash Muralitharan told Al Jazeera a burn can look dead, smoulder for weeks, and flare again. Only sustained rain soaks the soil enough to end it. He hoped that rain would come by the end of September or October 2026, and called firefighting until then “only a temporary solution.” The BBC has reported the same limit. Peat can burn underground for months.
In 1997, the Associated Press later wrote, hundreds of fires between July and November sent haze across much of Southeast Asia. On 1 March 1998, AP’s Geoff Spencer reported fires still burning around Balikpapan and Samarinda, which should have been in the wet season. Meteorologists blamed El Niño. Dr Jusuf, head of a state hospital in Samarinda, said, “We could face major health problems if it does not rain soon.” The government estimated at least 34,600 acres burned since January; others estimated as many as 247,000 acres. The outbreak was still active more than half a year after it began.
In 2015, The Guardian reported about 100,000 fires in Indonesia’s peatlands since July, thousands of them inside primary forest and national parks. By 26 October no rain was expected for at least a month, and Palangka Raya had closed schools for five of the previous seven weeks. Reuters reported on 12 November that rain had doused some fires, but Martin Wooster of King’s College London said the smoke had lasted “for weeks, even months.” Scientific American wrote that crews were drilling more than 20 metres down for water, and that if the drought held the season could run into 2016. The magazine said more than two million hectares burned. Reuters, citing later government data, said 2.6 million. Mongabay used that official figure too. A paper in iScience cited a separate estimate of 4.6 million hectares across Sumatra, Kalimantan and West Papua.
The disaster agency told the BBC that 328,724 hectares burned from January through August 2019, with Central, West and South Kalimantan among the worst hit. By the end of September the ministry told Reuters the total was 857,756 hectares. Mongabay put Kalimantan’s share at 4,281 square kilometres, ahead of Sumatra, with about a quarter of the national burn on peat, and said the ministry found 93 percent of fires on land with no standing forest. David Gaveau, then at the Center for International Forestry Research, told Mongabay the smoke was likely coming from idle peat deforested by earlier fires. Hotspots fell from 16,429 in September to 3,054 in October as rain reached Kalimantan. Reuters later reported a World Bank estimate of at least $5.2 billion in losses. A satellite study Reuters covered in 2022 found 3.1 million hectares burned, against the ministry’s roughly 1.6 million. The 2026 season, Al Jazeera reported on 1 September, had already burned more than 200,000 hectares on Borneo and Sumatra between January and July, nearly 95,000 of them in July. Hotspots in West Kalimantan nearly doubled in a day, to 7,377.
People
The rooms that stay shut
In October 2015, Palangka Raya’s meteorology office told The Guardian of a “very dangerous” PM10 reading of 2,483, with visibility under 30 metres in 350 places. Clinics had logged 5,931 acute respiratory infections since July, about 3 percent of the city. A resident described Hari Kuning, yellow days, when the smog swallowed the sun, and said masks on sale were “ridiculously inadequate.” Verchot told Reuters that an official count of half a million sickened was “the tip of the iceberg.” Rural patients, he said, seek care only when they are very ill. Local media cited by Reuters reported at least 10 deaths and 504,000 people sickened on Borneo and Sumatra. His team found ozone, carbon monoxide, cyanide, ammonia, formaldehyde, nitric oxide and methane in the smoke. In a hotel kilometres from the flames, Wooster measured carbon monoxide high enough to trip a household alarm. Near the peat, fine particles passed 1,000 micrograms per cubic metre and sometimes reached 2,000, against a U.S. Environmental Protection Agency hazardous threshold of 300. The BBC later put the crisis at $16 billion, more than 500,000 respiratory illnesses, and a state of emergency. Scientific American reported more than 1.5 billion tonnes of carbon dioxide from the fires, more than Japan emits in a year.
September 2019 returned Palangka Raya to that air. Greenpeace Indonesia told the BBC the index hit 2,000. “I haven’t opened the windows and doors for two weeks,” Lilis Alice said. “In the morning, it’s dark.” Ilham said the smoke reddened his wife’s face and that the emergency room named it as the cause. Reuters reported school closures, oxygen at clinics, and days of “dangerous” readings. Antara reported classes cancelled from kindergarten through university, and flights grounded at Tjilik Riwut Airport. Citing the World Bank, Reuters later wrote that 900,000 people reported respiratory illness.
On deaths, the published record splits and stays split. Harvard and Columbia estimated in Environmental Research Letters that the 2015 haze caused 100,300 premature deaths: 91,600 in Indonesia, 6,500 in Malaysia and 2,200 in Singapore. Agence France-Presse noted an official Indonesian toll of 19. The model counted only adults and only PM2.5. Two days later the Associated Press reported that Indonesia, Malaysia and Singapore rejected the research. The disaster agency called it possibly “baseless.” AP’s official figure was 24 deaths, including firefighters. Malaysia’s health minister, Subramaniam Sathasivam, called the work “computer-generated, not based on hard data.” Study author Joel Schwartz told AP that Malaysian pollution during the haze was ten times the World Health Organization level linked to early death.
“I haven’t opened the windows and doors for two weeks. In the morning, it’s dark.”
Wildlife
Apes, and the animals no clinic can count
Wild orangutans live only on Borneo and Sumatra. Scientific American put the population near 50,000 in November 2015, about 78 percent below more than 230,000 a century earlier. More than half, Simon Husson said, live in peat. “Every one of these peatlands in Borneo right now is on fire, somewhere.”
The Guardian found the 2015 fires inside the forests that still held them. About 358 hotspots were recorded in Sabangau, which Harrison described as home to nearly 7,000 wild orangutans, the largest population anywhere. Fires were also in Tanjung Puting, home to about 6,000 apes; in Katingan, with about 3,000; and in Mawas, with about 3,500. Conservationists said a third of the world’s remaining wild orangutans were threatened — a statement about habitat, not a body count. Harrison named clouded leopards and hornbills in the same forests. Husson told Scientific American the forest also holds white-bearded gibbons, sun bears and pangolins, and that smoke had made canopy research impossible. The Guardian reported that little was known about the effect on wild lungs. Because they resemble human lungs, smoke was expected to sicken animals and stop them feeding.
The plainest account of animals found dead comes from March 1998. The Associated Press, citing Antara, reported that rangers in Kutai National Park, north of Samarinda, found remains of orangutans, small deer, snakes and porcupines. Fires were also burning in Bukit Suharto conservation park. That week officials saved at least eight orangutans, four of them babies. Two others were found dead in traps. Mothers, AP noted, are sometimes killed so the young can be sold as pets.
In 2019 the counts come from clinics. On 17 September Antara reported dozens of orangutans with acute respiratory infections at the Borneo Orangutan Survival Foundation’s Nyaru Menteng centre, adults and infants under five, in cages and at a forest school near burned land. Veterinarian Viet said some recovered and then relapsed, and that staff were dosing them with vitamins and a herbal mix made from onion. The foundation said that day that 37 young orangutans were suspected of mild infection and were on nebulisers, antibiotics and vitamins, and that smoke put all 355 apes there and on nearby islands at risk. Tempo, quoting Nico Hermanu, reported 37 sick, six of them adults. A fire in early August had come within 300 metres of the fence. At Samboja Lestari in East Kalimantan, thin smoke hung over 130 orangutans, who were given milk and vitamins while forest school was cut short. No new infections had been logged there, though the foundation warned of bronchitis and pneumonia. In the Mawas peatlands, 309,000 hectares in Kapuas and South Barito, 80 hectares were burning, 20 of them near the Tuanan research centre. Chief executive Jamartin Sihite said no wild orangutan had yet been rescued or moved.
A paper in iScience followed four wild males at Tuanan through the 2015 haze. They called less often, and the calls were lower and harsher, a change the authors compared with smokers’ voices. Most of the change was still there two months later. The authors say four animals “greatly limits the interpretation.” The paper also notes that white-bearded gibbons called less on smoky days in 2006. No outlet cited here has published a death toll for sun bears, pangolins, hornbills or gibbons.
“Every one of these peatlands in Borneo right now is on fire, somewhere.”
Verchot told Reuters the haze was “totally preventable” if peat was no longer drained and degraded swamps were restored. Greenpeace called for the land to be reflooded. In 2015, President Joko Widodo told the BBC the country needed at least three years. Rain is still what ends a peat fire. Until it comes, a child in Kuching and an orangutan in Central Kalimantan are breathing the same season.
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