At the age of 13, Tan Yi Han could not see the edge of his schoolyard. It was 1998 in Singapore, the wealthy city-state known for its tidy streets and clean, green image. But for much of that particular school year, clouds of smoke shrouded the skyline. The record-setting air pollution, which had begun in 1997 and lasted for months, caused a 30% spike in hospital visits. It would later be remembered as one of South East Asia’s worst-ever “haze episodes”.

Haze episodes have occurred in South East Asia nearly every year since. Back in 1998, and for years afterwards, Tan didn’t think too deeply about them. Yet at some point in his late 20s, he began to wonder: where did the haze come from? And why did it keep coming back?

Despite growing fears that this haze could cause serious health issues, the problem remains as opaque as the smoke itself.

Charcoal landscape

In the summer of 2013, a plane carried Tan over the Straits of Malacca to Pekanbaru, the capital of Riau province, the largest palm-oil production region in Indonesia. Tan, then a 28-year-old financial consultant, was volunteering with the Global Environment Centre, a Malaysian group that has worked for years to prevent and mitigate haze. He travelled to the heart of neighbouring Indonesia, just after a record-breaking haze episode hit peninsular Malaysia.

On a driving tour in Riau, he saw endless acres of burned-out landscapes. Fires had turned swampy peat bogs, the area’s natural vegetation, into land whose parched surface resembled charcoal. These fires dry out the peatlands for agricultural uses, mainly the cultivation of oil palms. But in some villages, fires had even destroyed existing oil palm trees that belonged to multinational companies or local farmers.