ASEAN’s extreme heat challenge: Why passive cooling could become a critical solution for workers and cities

As temperatures across Southeast Asia continue to climb, a new regional roadmap warns that extreme heat is no longer only an environmental issue, but a growing threat to health, productivity, energy systems, and urban liveability.

Extreme heat is increasingly reshaping daily life across Southeast Asia, with cities facing rising temperatures, longer heatwaves, and growing pressure on energy systems. Against this backdrop, the ASEAN Centre for Energy has introduced a new roadmap focused on passive cooling strategies to help ASEAN countries better protect communities from rising heat risks.

Titled Roadmap for Extreme Heat Protection through Passive Cooling in ASEAN Region, the report outlines how urbanisation, climate change, and rising energy demand are intensifying heat exposure across the region.

The roadmap defines extreme heat as temperatures that significantly exceed the historically normal range for a region, typically involving sustained daily maximum temperatures above 35°C. According to the report, June 2024 marked the 13^th consecutive month of record-breaking global temperatures. Dense urban development, shrinking green spaces, and heat-absorbing infrastructure are also worsening the Urban Heat Island (UHI) effect, turning many cities into heat traps.

The report noted that vulnerable groups including women, children, older persons, low-income households, and informal workers are disproportionately exposed to heat-related risks. Women, in particular, often experience prolonged indoor heat exposure due to unpaid caregiving responsibilities and limited ability to make housing improvements.

Across ASEAN, urban populations are projected to rise from 348mn people in 2022 to 521mn by 2050. By 2080, up to 1.1bn urban dwellers in South and Southeast Asia could face extreme heat lasting more than 30 days annually.

Pert the report, cities including Bangkok, Manila, and Jakarta are already experiencing dangerous heat levels. At the same time, growing reliance on air-conditioning is placing heavier strain on national power grids while remaining financially out of reach for many vulnerable communities.

Against this backdrop, the roadmap outlines ASEAN’s plan to address rising temperatures, growing energy demand, and climate risks caused by extreme heat and rapid urbanisation. It focuses on the built environment, where cooling systems such as air conditioners and fans are driving a sharp increase in electricity use and carbon emissions.

The roadmap also highlights passive cooling solutions, such as better building design, natural ventilation, and shading, as affordable and accessible ways to reduce reliance on air conditioning. Covering the period from 2026 to 2050, it provides policy guidance, design recommendations, financing approaches, and implementation strategies that ASEAN countries can adapt to their own needs and conditions.

More broadly, it seeks to drive greater focus to ASEAN’s wider climate and energy goals, including energy efficiency targets, the Paris Agreement, and the Global Cooling Pledge. It places particular attention on vulnerable groups such as low-income households, older people, children, and people with disabilities. At the same time, it acknowledges challenges that could affect implementation, including inconsistent data, differing levels of technical and regulatory capacity across countries, limited access to climate finance, and underdeveloped supply chains for passive cooling materials. It notes that sustained political support, funding, and regional cooperation will be essential for the roadmap to succeed.

Temperatures are rising faster than expected

The roadmap projects significant temperature rises across the region's major cities by 2050:

• Bangkok: Average maximum temperature rises from 33.3°C (2000) to 38.1°C, with extreme heat days above 35°C increasing from 45 to 120 annually
• Ho Chi Minh City: Rises from 33.0°C to 37.7°C, with 115 extreme heat days projected annually
• Manila: Rises from 32.6°C to 37.2°C, with 110 extreme heat days projected annually
• Jakarta: Rises from 31.9°C to 36.4°

Four key climate trends are driving this: accelerating temperature increases, increasingly unpredictable monsoon patterns with longer dry seasons, longer heat seasons starting earlier in the year, and rising humidity pushing wet-bulb temperatures closer to the limits of human physiological tolerance.

Between 2000 and 2009, ASEAN averaged two to three significant heat wave events per year. By 2010 to 2019, that rose to four to six annually, typically lasting seven to ten days. From 2020 to 2024, the frequency climbed to eight to twelve events per year, with some persisting for three to four weeks. The impacts are direct: heat-related mortality and morbidity are increasing across urban Asia, outdoor worker productivity falls, electricity demand surges, and staple crops such as rice face heat stress during critical growth stages.

Who bears the heat most

The roadmap's climate vulnerability assessment scores each ASEAN member state on a scale of one to 10, combining exposure, sensitivity, and adaptive capacity. Myanmar leads at 8.7, followed by Cambodia at 8.2 and Lao PDR at 7.9, all facing high exposure with very limited capacity to respond. Indonesia sits at 7.1 and the Philippines at 7.4, with coastal communities and informal urban workers most exposed. Thailand scores 6.2 and Vietnam 6.8, while Malaysia and Brunei sit in the mid-range. Singapore scores 4.2, though even though the elderly and outdoor workers remain vulnerable.

Across all countries, children, older adults, pregnant women, and people with chronic conditions face heightened physiological risk. Low-income households, informal workers, and migrants are exposed through poor housing, overcrowding, inadequate ventilation, and limited access to cooling. Women face a distinct layer of exposure through unpaid care work indoors and limited control over housing conditions.

Three systemic gaps compound all of this: infrastructure deficits including poor building design and loss of urban green space, institutional gaps including absent heatwave early warning systems and fragmented cross-border coordination, and knowledge deficits including low public awareness and insufficient local research on heat-resilient urban planning.

The UHI effect

The UHI effect describes the elevated temperatures that dense urban areas experience relative to their rural surroundings, driven by heat-absorbing built materials, reduced vegetation, and altered land surfaces. It raises cooling energy demand, degrades air quality, and heightens heat-related illness risk.

In Jakarta, surface temperatures exceed rural surroundings by up to 6°C by day and 8.7°C at night. Bangkok records daytime UHI intensity of 5.4°C, Manila 5.8°C, and Kuala Lumpur 4.2°C. Singapore, with 47% green cover, records a comparatively lower daytime UHI intensity of 3.8°C against Manila's 5.8°C with just 5.1% green cover. To cope, urban greening interventions are expected reduce air temperatures by up to 4°C, offering a practical and accessible mitigation pathway.

As further detailed, low-income neighbourhoods sit disproportionately in the highest-intensity UHI zones, where poor insulation and minimal green space amplify thermal stress. Specifically, temperature monitoring in Malaysian cities has recorded dangerous indoor and outdoor heat levels particularly affecting children, the elderly, and low-income households.

Mitigation: Nature, buildings, and policy

The roadmap sets out three categories of urban heat mitigation:

• Nature-based solutions, whichinclude urban forestry targeting 30 to 40% tree canopy coverage, green corridors, vertical gardens, rooftop greenery, and restored urban waterways;
• Built environment interventions, which include cool roofing, reflective pavements, passive cooling requirements in building standards, and shading infrastructure, and
• Policy and planning measures, which include zoning reforms, green building codes, and development regulations promoting natural ventilation through appropriate street orientation and increased urban porosity.

On implementation, the roadmap is structured in three phases:

• From 2026 to 2027, emergency cooling shelters, public shade structures, cool roofing retrofits for schools and healthcare facilities, and rapid city-level heat mapping.
• From 2028 to 2035, mandatory passive cooling building codes, urban forest expansion, green infrastructure integration, and wind flow analysis in urban planning.
• By 2036 to 2050, full transformation of ASEAN cities into climate-resilient, heat-adaptive urban environments, with regional coordination on UHI mitigation and passive cooling embedded across all planning processes.

How buildings are making things worse

The situational analysis is direct about the building stock's role in compounding the heat crisis. Non-residential buildings, from office towers to hospitals and schools, commonly prioritise mechanical cooling over passive design. High-rise commercial buildings in financial districts are characterised by extensive glazed facades with limited consideration of solar orientation or natural ventilation.

In the residential sector, high-rise towers use generic design patterns with limited cross-ventilation. Affordable housing scores highest for occupant heat vulnerability, with small units, poor ventilation, and minimal passive cooling features. Traditional low-rise buildings with high ceilings, deep eaves, and courtyards score lowest, though the shift to concrete block construction has eroded much of this climate responsiveness.

Further, inadequate solar shading, poor natural ventilation, inappropriate material selection, insufficient insulation, and poor building orientation are consistently identified as the key design limitations driving up cooling loads. The root causes are familiar: developers prioritising floor area over thermal performance, weak building codes, inaccessible climate-appropriate materials, and no post-occupancy monitoring, it was highlighted.

The energy system cannot absorb this demand

Buildings account for 23% of total final energy consumption across ASEAN, with space cooling the fastest-growing driver. Air conditioners represent approximately 15% of residential energy use, with fans adding a further 9%. Space cooling electricity demand is projected to reach 300 TWh by 2040, roughly equivalent to the combined electricity consumption of Indonesia and Singapore.

Air conditioning penetration ranges from 80 to 90% in Singapore and Brunei to just 5 to 15% in Vietnam, the Philippines, Cambodia, Lao PDR, and Myanmar, where demand is projected to grow by 400 to 600% by 2030. A 3.6% energy demand increase in 2024 across the region was met entirely by fossil-based generation. The climate-energy feedback loop is clear: more heat drives more cooling demand, which drives more fossil fuel consumption, which drives more warming.

Passive cooling strategies and nature-based solutions are estimated to be capable of cutting global cooling capacity demand growth by 24% by 2050, avoiding up to USD3tn in equipment costs and cutting 1.3bn tonnes of CO₂-equivalent emissions.

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Lead image / ASEAN Centre for Energy