2. India stands out as one of the world’s most vulnerable countries. At 3°C of warming, more than half of India’s population and over 80% of its older adults could experience at least 180 hours of intolerable heat a year, on average.
3. In Delhi and the greater Indo-Gangetic Plain, older adults are projected to experience close to or more than 1,000 hours of intolerable heat a year at 1.5°C of global warming, expected around 2030. At 3°C, this rises to more than 2,000 hours.
4. “Importantly, these hours are not spread evenly throughout the year. They are concentrated between May and September,” according to Prof Qinqin Kong, lead author of the study.
5. At more than 3°C of warming, older adults could experience intolerable heat repeatedly during both day and night for several consecutive months, leaving little opportunity for the body to recover. Such exposure would put enormous pressure on access to cooling, electricity, health services and heat-response programmes, Prof Kong said.
6. Using a high-resolution heat-stress metric, the researchers modelled scenarios ranging from 1°C to 4°C of global warming above pre-industrial levels, in 0.5°C increments, alongside population projections.
7. At 1.5°C of warming, an estimated 22% of the world’s older adults—about 290 million people—would face unsafe heat for at least a month each year.
8. The study defines this as at least 180 hours of dangerous heat annually, assuming roughly six hours of such exposure per day. Young adults would not face a similar level of risk until 4°C of warming, when 17%—about 490 million people—would be affected.
9. Each additional degree of warming exposes roughly one billion more people to temperature-humidity combinations beyond which the body can no longer maintain its heat balance.
10. The greatest exposure is concentrated in tropical and subtropical regions, particularly South Asia, the Persian Gulf, West Africa, Southeast Asia and eastern China. Many of these areas are densely populated and have fewer resources for adaptation.
(Infographic generated by AI)
Why are older people more vulnerable?
11. Prof Kong said older people face serious health risks from heat at lower temperatures than previously estimated.
12. Previous studies relied heavily on measurements from healthy young adults to determine when temperature and humidity would become challenging for the human body.
13. Older people are generally less able to regulate body temperature: they sweat less, their blood vessels respond more slowly and their hearts work harder in the heat.
14. As a result, earlier studies may have underestimated the number of people at risk from extreme heat by at least two-fold, she said.
Why are heat warnings alone not enough?
15. Dr Golechha said heat-health strategies must go beyond issuing warnings and identify those most vulnerable to heat. “Provide special alerts and assistance for the elderly, people living alone, people with chronic illnesses, people living in poorly ventilated homes, and people without reliable cooling,” he said.
16. The authors also called on governments to develop heat-emergency plans and improve access to cooling and heat-warning systems. Cutting emissions, they said, remains essential to reducing older people’s risk of prolonged, round-the-clock heat and protecting future generations from widespread heat exposure.
How vulnerable are children to heat stress?
1. Another new research from Vrije Universiteit Brussel (VUB) finds that up to 560 million children aged 0-9 globally — 43% of all children in this age group — are experiencing at least one additional month of heat stress every year because of human-induced climate change.
2. In India, the number is 145 million children, or 61% of those aged 0-9. The VUB analysis shows that climate change has already doubled the number of Indian children aged 0-9 exposed to at least five total months of dangerous heat stress each year — from 59 million to 118 million, or 50% of children in this age group.
3. The projections become starker with further warming. In a 1.5°C warmer world, around 166 million Indian children (74%) aged 0-9 are projected to experience at least one additional month of heat stress each year. Around 123 million (55%) could experience at least five total months, or 150 days, of heat stress.
4. In a 2°C warmer world, the number experiencing at least one additional month of heat stress could rise to 169 million (96%), while around 120 million (68%) could experience at least five total months.
5. The study, published in Science Advances, combined population data with state-of-the-art climate models and attribution science to determine how much of this exposure can be linked specifically to human-induced climate change.
6. According to Rosa Pietroiusti, lead author of the study and a PhD researcher at VUB, children’s exposure is higher than that of any other age group. It is also nearly three times the number of people aged 60-69 — about 190 million, or 30% of that age group — experiencing at least one additional month of heat stress.
Why are children more vulnerable to heat stress?
7. The findings are particularly concerning because children are physiologically more vulnerable to extreme heat. Their bodies heat up faster than those of adults, they sweat less efficiently and they depend on adults to keep them hydrated, rested and protected.
8. Excessive heat can disrupt the body’s normal functioning and, in severe cases, cause dehydration, heatstroke and organ failure. It can also interfere with learning and cognitive development.
9. The study focuses on humid heat, which can be more dangerous than dry heat because high humidity prevents sweat from evaporating efficiently, making it harder for the body to cool itself.
10. As climate change makes heat waves more frequent and intense, children are increasingly exposed to conditions in which their bodies struggle to regulate temperature.
11. The risks are not evenly distributed. Children from low-income families can be particularly vulnerable because they may have fewer options to escape the heat — whether through air-conditioning, reliable electricity, access to cool spaces or the ability to alter school and travel routines.
12. For Wim Thiery, senior author of the study and professor at VUB, the findings underline the need for urgent action. Protecting children from the worst impacts of climate change will require policymakers to drastically reduce fossil-fuel emissions and limit warming in line with the Paris Agreement.
BEYOND THE NUGGET: Wet bulb temperature
1. Wet bulb temperature is not the regular temperature we see on weather apps. It is a measure that combines heat and humidity to show how stressful the environment actually feels to the human body.
2. Notably, the body depends on sweating to maintain a stable internal temperature. When humidity rises sharply, sweat cannot evaporate efficiently.
3. When the wet-bulb temperature exceeds 35°C, human bodies cannot radiate the heat produced by our basic metabolic activities. Prolonged exposure to such heat is lethal. Some scientists put the limit at a wet-bulb temperature of just 31°C.
4. As per Dr Sundar Krishnan, senior consultant, internal medicine, KIMS Hospitals, Thane— “This traps heat inside the body and increases the risk of dehydration, heat exhaustion, muscle cramps, dizziness, and in severe cases, heatstroke. Once the body loses its ability to cool down effectively, it can become a medical emergency very quickly,”
5. Traditionally, it is measured using a thermometer wrapped in a wet cloth. “As water evaporates, the temperature drops. But if the air already contains a lot of moisture, evaporation slows down, and the reading remains high. Today, weather agencies use advanced calculations involving humidity, air temperature, wind speed, and atmospheric pressure to estimate wet bulb temperatures more accurately,” said Dr Sundar.
Post Read Question
The World Bank warned that India could become one of the first places where wet-bulb temperatures routinely exceed 35°C. Which of the following statements best reflect(s) the implication of the above-said report? (UPSC CSE, 2025)
1. Peninsular India will most likely suffer from flooding, tropical cyclones and droughts.
2. The survival of animals including humans will be affected as shedding of their body heat through perspiration becomes difficult.
Select the correct answer using the code given below:
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: (c)
(Source: Over 80% of India’s elderly could face dangerous heat stress at 3°C global warming, says Lancet study,Climate change heat stress puts 145 m Indian children at risk of dehydration, heatstroke: Study, What is wet-bulb temperature, and why is it being discussed during heatwaves?)
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As climate change makes heat waves more frequent and intense, children and elderly are increasingly exposed to conditions in which their bodies struggle to regulate temperature. (Image: AI generated) 
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