The Southeast Asian haze is a fire-related recurrent transboundary air pollution issue. Haze events, where air quality reaches hazardous levels due to high concentrations of airborne particulate matter from burning biomass, have caused adverse health, environmental and economic impacts in several countries in Southeast Asia. Caused primarily by slash-and-burn land clearing, the problem flares up every dry season to varying degrees and generally is worst between July and October and during El Niño events. Transboundary haze in Southeast Asia has been recorded since 1972 with the 1997 and 2015 events being particularly severe.
Industrial-scale slash-and-burn practices to clear land for agricultural purposes are a major cause of the haze, particularly for palm oil and pulpwood production in the region. Burning land occurs as it is cheaper and faster compared to cutting and clearing using excavators or other machinery. Fires started for this purpose sometimes spread and create forest fires, worsening the problem. The high concentration of peat in soil contributes to the haze's density and high sulphur content.
Fires in Indonesia (particularly South Sumatra and Riau in Sumatra, and Kalimantan in Borneo), and to a lesser extent in Malaysia and Thailand, have been identified as sources. The haze regularly has a major impact on air quality in Indonesia, Malaysia, Singapore and Brunei Darussalam; to a lesser extent and in particularly severe years, it also impacts the Philippines, Thailand, Vietnam, Cambodia and countries outside the region.
Haze events have been shown to cause health issues and mortality in affected areas, and have caused disruption to economic activity and education as sectors are forced to close to minimise exposure to hazardous air. The haze also has a substantial environmental impact, being a major contributor to greenhouse gas emissions in the region and affecting wildlife and ecosystems.
The haze is an international issue which has caused regional political tensions. Efforts have been made to mitigate haze events and their impacts, and some relevant frameworks for regional cooperation among ASEAN countries have been introduced. Challenges remain in implementing these, and mitigation efforts have failed to prevent haze from reoccurring.
