For weeks on end, parts of Indonesian Borneo have resembled an Armageddon landscape with masked residents immersed in a putrid, red-brown haze as wildfires devour peatlands near homes and farms.
Burning slowly, mostly under the surface and sometimes for months on end, peatland fires are responsible for much of the dry season haze that this year has tainted air as far afield as Malaysia, Singapore and the Philippines.
Peatlands are composed of organic material that does not completely decompose in water-logged conditions and has settled over thousands of years into a layered soil-like substance.
Healthy peatlands are home to diverse plants and trees like nutmeg and durian, and animals that can include endangered orangutans, clouded leopards, Sumatran tigers, sun bears and tapirs.
They are porous and absorbent, making them critical for flood containment.
While they cover only about three per cent of global land, peatlands store about a third of the world's soil carbon — double that trapped by forests.
Indonesia has the world's biggest share of tropical peatland, about a third of the global total.
Of Indonesia's estimated 24.2 million hectares of peatland, 16.4 million hectares have been degraded and are vulnerable to fire, according to the Pantau Gambut non-governmental organisation.
The culprit is mainly industrial-scale plantations for timber, pulp and paper, padi and palm oil, of which Indonesia is the world's biggest producer by far.
To cultivate peatlands, they are drained with canal networks that in Indonesia span about 285,000km, according to Pantau Gambut research — seven times the circumference of Earth.
The water runs into rivers or the sea, leaving the dried-out peatlands vulnerable to burning, especially in strong El Nino years that can bring severe drought to Indonesia.
Peatland fires are often imperceptible but for the foul smoke they emit and the heat they generate underfoot.
The many layers of thick carbon can keep smouldering in "zombie fires" for weeks, and are hard to put out.
While less than a third of wildfires in Indonesia are on peatlands, they produce most of the haze, according to Greenpeace research.
This toxic smog contains harmful elements, including formaldehyde, hydrogen cyanide and ammonia, as well as PM2.5 particles small enough to penetrate the lungs or bloodstream.
The World Health Organisation has linked PM2.5 exposure to increased illness and death.
By Oct 6, Indonesian wildfires had emitted 140.5 megatonnes of planet-warming carbon, around 13 per cent of the global total this year, according to the Copernicus Atmosphere Monitoring Service.
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