The Association of Southeast Asian Nations’ (Asean) efforts to control transboundary haze will face increasingly severe tests as climate change brings hotter and drier conditions, according to policy think tank Singapore Institute of International Affairs (SIIA) chairman Simon Tay.
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The SIIA has studied transboundary haze for nearly three decades and publishes an annual risk assessment combining weather data with government, corporate and land management factors.
Indonesia’s transboundary haze is a recurring regional problem caused largely by forest and peatland fires, including those associated with land clearing and agricultural burning in Sumatra and Kalimantan. Although Asean adopted a transboundary haze agreement in 2002, prevention remains difficult because it requires sustained land management, consistent enforcement and greater transparency around concessions and corporate supply chains.
“Asean has made progress, but the challenge is ensuring that prevention and sustainable practices are maintained on the ground and across supply chains,” Tay told Eco-Business. “With climate change bringing hotter and drier conditions, these systems will be tested more severely and more often.”
His warning gained urgency as smoke from Indonesian forest and peatland fires reached the Philippines on 1 September, after causing prolonged disruption in Malaysia and affecting Brunei in August, while putting Singapore on alert.
Such episodes are historically less frequent in the Philippines. The last clearly documented case occurred in 2015, when Indonesian smoke reached Mindanao, disrupting flights and prompting health warnings. By contrast, Malaysia and Singapore face transboundary haze on a near-annual basis, although severe incidents are less common. Brunei is also regularly exposed, particularly when fires intensify in Kalimantan.
The SIIA’s Haze Outlook released in June, rated the risk of a severe transboundary haze incident affecting Brunei, Indonesia, Malaysia and Singapore during the remaining months of 2026 as “red”. It identified August and September as the peak danger period, driven by El Niño and the Indian Ocean Dipole.
Malaysia has experienced some of the most prolonged disruption since Indonesia’s forest and peatland fires intensified. Hazardous air pollution affected several parts of Sarawak, prompting school closures and the cancellation of outdoor Independence Day celebrations at the end of August.
The crisis spread northward on 1 September, when smoke from fires in Kalimantan reached the Philippines, particularly Metro Manila, Central and Southern Luzon and parts of the Visayas, as strong southwest monsoon winds transported smoke towards the country, Philippine authorities said.
Monitoring stations recorded “very unhealthy” and “acutely unhealthy” air quality, prompting the suspension of in-person classes in some areas. Health and local government officials advised residents to limit outdoor activity and wear well-fitting masks, preferably N95 masks.
Children, older people and those with respiratory or cardiovascular conditions were urged to take additional precautions and remain indoors where possible.
Gerry Bagtasa, a professor at the University of the Philippines’ Institute of Environmental Science and Meteorology, said the continued use of open burning makes regional haze difficult to prevent despite national laws and local ordinances.
“Burning remains the cheapest and fastest way to get rid of agricultural waste or clear land, so there is not enough motivation, financial or otherwise, to move away from burning,” Bagtasa told Eco-Business.
Most haze episodes in the Philippines originate from local emissions, he added. The country only occasionally receives pollution from East Asia during spring and smoke from Indonesia during summer.
Transboundary pollution has therefore not traditionally ranked among the Philippines’ most persistent environmental problems, Bagtasa said, “but that may change”.
Philippine environmental authorities warned that the latest haze could persist while Indonesian fires remain active and southwest monsoon winds continue carrying smoke northward.
Prevention requires sustained investment
Tay said better preparedness requires governments to invest continuously in prevention rather than waiting until smoke has already crossed borders.
“Prevention is harder because it requires sustained investment in communities, land management and enforcement even when the skies are clear,” he said, adding that it will be part of the discussion at an upcoming SIIA-World Resources Institute Indonesia dialogue in Jakarta next week, looking at what is already being done and what more can practically be done to strengthen fire prevention.
Tay also called for consistent enforcement and greater transparency around concessions and corporate supply chains, saying these could help governments and companies respond earlier and more effectively.
“Enforcement needs to be consistent, while greater transparency can help everyone act earlier and more effectively,” Tay said. “Asean can play a role in strengthening regional cooperation and information-sharing, while governments and companies can improve transparency around concessions and supply chains.”
“Ultimately, governments, businesses and financial institutions all have a part to play in preventing haze.”
