Indonesia's fire crisis: Super El Niño intensifies toxic haze affecting millions across Southeast Asia

Across the islands of Borneo and Sumatra, fires have been burning for months. Some are set deliberately—a cheap method for clearing land to plant oil palms, a crop Indonesia produces more of than any other nation on earth. The practice has a name: slash and burn. What begins as a controlled clearing often spirals into something far larger. In the heat and drought of this year's conditions, the flames spread across borders, turning the air itself into a public health emergency affecting tens of millions of people.

The fires are worst on peatland—soil that has been drained and dried over decades of forest degradation. These are fires of a different order. They burrow underground, resurface elsewhere, and can smolder for weeks. David Gaveau, a landscape ecologist who tracks fires and deforestation across Asia through his organization Nusantara Atlas, describes them as the accumulated consequence of fifty years of forest loss. NASA has called tropical peatland fires an apex predator among wildfires—nearly impossible to stop once they take hold.

The numbers this year are staggering. Since January, nearly 896,000 hectares have burned across Indonesia. That is 34 percent worse than 2019, a year that itself was catastrophic. Gaveau says the trend is climbing higher still—worse than 2023, worse than the year before. "This is a terrible year," he said in recent weeks. The hardest-hit regions are Sumatra, Kalimantan (the Indonesian portion of Borneo), and Papua. In early September alone, fires in Indonesia released 19.7 million metric tons of emissions, accounting for more than a third of the global total.

The smoke has turned cities into something unrecognizable. In Kalimantan, photographs show streets shrouded in a thick, sepia-colored haze so dense it obscures buildings. Children sit at school desks wearing masks. Rescuers have had to administer oxygen to orangutans overcome by smoke. Ely Marlina, a 46-year-old schoolteacher and volunteer firefighter, described the experience of living inside it: the family has not opened doors or windows in weeks. Ash and smoke seep into the house regardless. At night, everyone sleeps while breathing in the fumes. Her eyes sting and water constantly. The dizziness is relentless. She worries that if the family continues breathing this air, their bodies will simply fail.

The public health impact is measurable and severe. Respiratory illnesses linked to the fires more than doubled in affected provinces between September 1 and September 9—from roughly 50,900 cases to 113,336. Emergency rooms have been overwhelmed. Schools have shut down. Air quality monitors tell the story in numbers. A healthy air quality index ranges from 0 to 50 and is marked in green. Anything above 300 is hazardous. On September 10 in Sampit, central Kalimantan, the index reached 1,142—a rating so extreme it exists in a category of its own, colored maroon. Every single day in September, Sampit's air has been classified as hazardous. In Kuching, Malaysia's largest city on Borneo, the index has fluctuated between unhealthy and hazardous throughout the month. One resident described breathing the air as equivalent to smoking a cigarette.

When smoke crosses international borders, it is called transboundary haze. This year, the haze has blanketed parts of Malaysia, Singapore, Brunei, and even reached the Philippines. Monsoonal winds carried it as far as Manila, where residents were urged to stay indoors and wear masks outside. Malaysia has called for the Association of Southeast Asian Nations to review a 2003 agreement on transboundary haze—a sign of how severe the problem has become.

Indonesia's government has responded with enforcement and resources. The environment ministry is investigating 19 companies allegedly connected to the fires. Police have arrested 113 people suspected of lighting them. The country has deployed planes, helicopters, drones, and military personnel to fight the blazes. Malaysia has sent three helicopters, an aircraft, and 52 personnel. Japan has contributed helicopters and firefighting teams. At the community level, a group of female firefighters called the Power of Mama conducts daily surveillance and outreach, urging people not to burn. In West Kalimantan, volunteers are going door-to-door distributing oxygen cylinders to residents and firefighters who cannot breathe—a campaign called Oxygen House.

But the worst may not have passed. This year's super El Niño—an unusually powerful version of the climate pattern that brings drought to Southeast Asia—has intensified the crisis. Experts warn that fires could peak in September and continue burning until November, when the rainy season typically begins. Gaveau notes that El Niño is an enabler: the more powerful it is, the longer and more intense the drought. But drought alone does not start fires. "You need a match," he said. "And we know what that is; it's people." Indonesia's forestry minister Raja Juli Antoni has warned the country is entering a critical phase. "September is our month of struggle," he said, "our field of struggle."