Haze from forest fires in Indonesia is choking parts of the country as well as neighboring Malaysia and Singapore. It has intensified in recent days, putting air pollution at hazardous levels as well as disrupting flights and outdoor activities. In Singapore, schools have closed and exasperated officials continue to offer assistance in fighting the fires. The Indonesian government has said it is taking steps to deal with the problem. Earlier this week it suspended the operating permits of three plantation companies thought to be setting fires to clear land for agriculture, and revoked the license of another.

#1: What is causing the haze and why?

The haze comes from fires set to clear forest land for agriculture, often palm-oil plantations. It is an annual occurrence but many researchers say it is worse this year because of severe drought caused by El Nino. Herry Purnomo, a researcher at the Center for International Forestry Research, says clearing land by fire is fast and about 10 times cheaper than using machinery. Demand for cleared land has risen alongside demand for palm oil, which is found in a wide variety of products including shampoo and ice cream, he said. Indonesia is the world’s biggest producer of the commodity and plantations owned by Indonesian, Malaysian and Singaporean companies earned about $18.4 billion in revenue last year, Mr. Purnomo said.

#2: Where are the fires occurring?

Mostly in Sumatra and in Kalimantan, the Indonesian portion of Borneo. These once forest-rich islands are now largely covered in plantations. Environmentalists often point to plantation firms as the fires’ culprits. Companies say it’s mostly local actors. Unclear land ownership adds to the finger pointing. Many parties are involved, and the fires happen in state forests, community-owned land and within plantation company concessions, Mr. Purnomo said. According to Global Forest Watch, an online forest monitoring system created by the World Resources Institute, about 35% of the fires over the past week occurred in pulpwood, palm oil or logging concessions.