Indonesia Fires Choke Region, Top World Emissions

"We do expect to see some fires across the region at this time of year, but with El Niño, it clearly just gives a big enhancement to them," said Mark Parrington, a senior scientist at the Copernicus Atmosphere Monitoring Service in Bonn. "It's much drier, it's hotter, and when there's ignition, these fires burn in a far more extreme way."

Parrington also warned the data may understate the damage: peat fires burning underground or at low temperatures can fall "below the detection limit of the sensors, which means we're not actually seeing them."

Indonesia's environment ministry told Reuters it viewed the hazardous readings in Kalimantan and elsewhere "with concern," but said the Copernicus figures do "not directly reflect air quality conditions in a specific area" and that other factors had to be considered.

Environmental groups blame the draining of peatland for commercial plantations, including palm oil. "By draining away the water … companies leave the previously fireproof landscape like a ticking carbon time bomb," said Belgis Habiba, a forest campaigner with Greenpeace Indonesia.

Herry Purnomo of the Center for International Forestry Research said El Niño "does not necessarily create every fire, but it greatly intensifies existing fires and allows them to spread more easily." He does not expect a repeat of 2015, arguing Indonesia has "strengthened prevention, monitoring, and response measures."