That extreme heat is one of the main causes of death related to weather phenomena was already undeniable scientific evidence. Now, a study published in The Lancet Planetary Health once again alerts the scientific community by showing that prolonged high temperatures will affect a broader part of the population than expected. Also outside the summer months.
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In 2025, the annual report published in the journal Global Earth System Science Data (ESSD) already announced that the global thermometer had risen to 1.37 °C, due to global warming derived from human activities. The study published this Monday by scientists from American universities points out that if the global temperature reaches 1.5 °C above pre-industrial times, 22% of the population over 60 years old will be exposed to temperatures that could cause “hyperthermia,” a medical condition that occurs when the body is unable to regulate an excessively high body temperature.
This situation can worsen pre-existing conditions and diseases—especially those related to the cardiovascular, respiratory, and renal systems—as well as cause death in severe cases.
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Over time, the body loses the ability to regulate body temperature
Although other studies had already analyzed the consequences of global warming on the body, they established the same temperature limit for all population groups analyzed, regardless of age. However, older people tolerate heat worse because, over time, the body loses the ability to regulate body temperature.
By introducing different temperature limits for each age group, the study concludes that more than twice the previously estimated population would be exposed to 180 hours or more of heat above a healthy and tolerable limit for the human body. What the American scientists call uncompensable heat stress.
With global warming of 1.5 °C, older people will have a higher heat risk than people aged 18 to 34 with warming of 4 °C. According to the study’s authors, with this new data “the magnitude and geographic extent of the projected risk increase considerably compared to what was indicated in previous reports.”
South Asia and the Persian Gulf, the areas most affected by heat stress
On the other hand, the American scientists warn that if global warming is not stopped, the consequences could be much worse, and not only for older people. The study pays special attention to the areas of South Asia and the Persian Gulf, where it is expected that if a 3 °C rise due to global warming is reached, older people will suffer continuous heat stress for three consecutive months, both day and night.
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Additionally, the study identifies 13 especially vulnerable countries. India, Pakistan, Bangladesh, Myanmar, and Niger are identified as especially vulnerable countries, exceeding poverty rates of 50%, having at least 10 million or 80% of older adults in their total population, and experiencing more than 180 hours annually of heat limit excess. India is the country with the largest exposed population, followed by China and Pakistan. The three countries together represent 72.6% of the 2.03 billion people who would be exposed.
A 4 °C rise would put the young population of eastern USA and much of South America at risk
The study determines that if the temperature reaches a global warming of 2 °C, exposure to “uncompensable heat stress” would extend to the population aged 40 to 59 in the African Sahel. Each additional degree of warming endangers about 1 billion more people per year.
Also, in the event of a 4 °C rise, the population aged 18 to 34 in the eastern United States and much of South America could be unable to cope with extreme temperatures. The regions of eastern China, the Persian Gulf, and the Sahel would exceed 180 hours of annual exposure, while 540 hours would be reached in the great northern plain of India and Pakistan, one of the most populated areas on the planet.
Limiting global warming to 2 °C could protect young people from extreme heat
The scientists also analyze the response of the population of eight cities, selected for “their large population, intense heat stress, and having different climate regimes.” For each city, they calculated the probability of suffering uncompensable heat stress through simulations of warming between 1.5 °C and 4 °C over the next 27 years. The results were also clear: if global warming is limited to 2 °C—preferably 1.5 °C—the exposure of “young adults,” aged 18 to 34, to heat conditions above the tolerance threshold would be considerably reduced. The effect would be less reversible for people aged 40 to 59.
Still, some cities are not free from this risk. In the case of Dubai, even if global warming were limited to 1.5 °C, the city could experience around 1,000 hours of heat stress. With these simulations, the study aims to serve as a guide for designing future environmental public policies. “Our findings can serve as a basis for specific heat action plans and to guide resource allocation and response planning,” the authors note.
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