Delhi, Karachi, Shanghai, Dhaka, Manila, Seoul, and other such densely built Asian megacities could face an additional 2-7 degrees Celsius (°C) spike in local temperatures on top of global warming, by the end of century, new analysis has warned.
Even with world limits warming to 1.5°C to 2°C, the urban heat island effect could push everyday temperatures in these cities several degrees beyond the global average, according to the United Nation’s 2025 Asia-Pacific Disaster Report.
In South and Southwest Asia, India, Pakistan and Bangladesh may endure over 300 days annually with a heat index above 35°C, with many regions suffering more than 200 days where it exceeds 41°C, the report, launched by the UN Economic and Social Commission for Asia and the Pacific (ESCAP) on November 26, highlighted.
Overall, the frequency of days above critical heat thresholds was set to increase sharply, with South and Southwest Asia, parts of Southeast Asia and northern and eastern Australia trending toward chronic heat exposure.
To assess future extreme heat risks across Asia and the Pacific, ESCAP used a ‘heat index’, which registered how hot it feels when relative humidity is also taken into account (also known as the ‘apparent temperature’). A heat index of 35°C and above counts as severe heat stress and prolonged exposure at this level poses health dangers. At 41°C, prolonged exposure represents extreme danger when a heat stroke becomes likely.
The index used four heat thresholds – 35°C; 37°C; 39°C; and 41°C, which the World Bank terms as ‘heat risk index categorization’. South and Southwest Asia were in heat index risk categories 3 and 4, reflecting not just prolonged exposure but also the highest levels of heat.
Southeast Asia also showed alarming increases, with nearly 30 per cent of the population projected to be exposed to extreme heat in business-as-usual scenarios. The South and Southwest Asia subregion consistently demonstrates the highest exposure across all scenarios, with over 40 per cent of the population projected to face heat index levels above 35°C and 41°C under both medium-and long-term futures, indicating chronic and intensifying risk.
In the last two years, while Asia and the Pacific was impacted by various natural hazards and climate-induced extreme events, the fastest growing climate-related hazards were driven by extreme heat.
The report showed how the disaster picture in the region was traditionally dominated by tropical cyclones and droughts. But today, rising temperature was exacerbating climate hazards and extreme events.
The year 2024 underscored how rapidly extreme heat was escalating across the region. It was the hottest year ever recorded globally, and much of Asia and the Pacific endured sustained and punishing heat episodes.
The most severe was the Bangladesh heatwave of April-May 2024, which affected an estimated 33 million people, making it the single disaster that impacted the greatest number of people in the region that year.
In India, an extended heatwave became the second deadliest event, claiming around 700 lives.
Overall, in Asia and the Pacific, between 2020 and 2024, the annual average reported disasters per year slightly exceeded the average of the previous decade. But the report said the real number is expected to be higher, given the typical delays and gaps in reporting.
According to EM-DAT, in 2024 alone, over 180 natural hazards and climate-induced extreme events were recorded.
The report found that South and Southwest Asia faced the highest exposure, with more than 40 per cent of the population expected to experience heat index levels above 35°C and even 41°C in both the medium and long-term scenarios, a sign of chronic and worsening risk.
The data considers two climate scenarios: where there is little progress in combating climate change and another in which climate change accelerates, driven by heavy use of fossil fuels. For each scenario, the report also considered short-term and long-term impacts.
With heat stress expected to surge across the region, heat-related mortality would potentially double by 2050, the report said. The urban poor were among the most exposed, especially in densely populated neighbourhoods where the urban heat island effect pushes temperatures even higher.
Extreme heat disrupts the body’s ability to regulate temperature, placing heavy strain on the cardiovascular and respiratory systems and worsening existing medical conditions. Heat-related illnesses ranged from cardiovascular and respiratory distress to kidney injury and heatstroke, while heat-induced trauma has been linked to lasting cognitive and cardiovascular impacts.
Meanwhile, extreme heat also deepens existing inequalities as higher-income communities typically occupy cooler, greener neighbourhoods. For example, a study in Bandung, Indonesia, found a temperature difference of up to 7°C between the hottest and coolest neighbourhoods.
It has been seen that access to cooling, clean water, and healthcare gets increasingly strained under rising heat, leaving children, older adults, and outdoor low-wage workers in dense, low-income urban areas disproportionately exposed.
As temperatures will climb, they will also interact with another threat: deteriorating air quality. Heat and pollution reinforce each other in a dangerous feedback loop that amplifies both climate and health risks.
“Greater heat increases the frequency of droughts and the intensity of wildfires, both of which release fine particulate matter (PM 10 and PM 2.5) into the atmosphere. Wildfires further contribute to pollution by emitting large volumes of carbon dioxide, carbon monoxide, nitrogen oxides and volatile organic compounds (VOCs), including acroline and formaldehyde,” it said.
On the contrary, only 54 per cent of global meteorological services issued warnings for extreme temperatures. The report noted that expanding heat-health warning systems in just 57 countries could save approximately 100,000 lives each year.
“Heat knows no borders; therefore, policy responses must anticipate impacts, reduce exposure and vulnerability at scale and safeguard those most at risk. With urgency, clarity and cooperation, lives and livelihoods across the region can be protected,” said UN Under-Secretary-General and Executive Secretary of ESCAP Armida Salsiah Alisjahbana.
As global temperatures rise, prolonged outdoor work, combined with high humidity and limited access to adaptive infrastructure causes a substantial increase in lost working hours. This has major implications for economic growth, income inequality and occupational health.
Across Asia and the Pacific, working hours lost to heat stress were projected to more than double from 3.75 million to over 8.1 million full-time job equivalents between 1995 and 2030.
This increase was a consequence of persistent exposure to extreme heat in labour-intensive sectors such as agriculture, construction and industry, particularly in South and Southeast Asia, which have large rural workforces and low adaptation capacity.
Beyond extreme heat, the region faces intensifying multi-hazard risks, from earthquakes and tsunamis to landslides, floods and cyclonic storms, that threaten critical infrastructure including transport networks, energy systems, water supply and telecommunications.
Using the Global Risk Model developed under the Global Initiative on Risk Information, the report provided a probabilistic estimate of long-term disaster costs, expressed as average annual loss (AAL).
Under every future scenario assessed, these losses were projected to climb sharply: from $418 billion under current climate conditions to $432 billion under the SSP1–2.6 pathway (IPCC scenario in which global carbon dioxide emissions are cut severely, but not as fast as required), rising even more steeply to $498 billion under the high-emissions SSP5–8.5 scenario (IPCC scenario in which current carbon dioxide emissions levels will roughly double by 2050). This surge reflected the compounded pressures of climate change, expanding exposure, and insufficient adaptation, particularly along high-carbon, growth-intensive development trajectories.
The report emphasised the need to place heat at the centre of multi-hazard planning, supported by heat-ready early warning systems that use interoperable alerting, agreed metrics and trusted last-mile communication.