A new global study has revealed that extreme heat is significantly limiting daily outdoor activity for people in India more than anywhere else in the world. Researchers say rising temperatures driven by climate change are reducing the number of hours people can safely spend outdoors, especially affecting the elderly and outdoor workers.
The study shows that India records around 100 billion people-hours of activity limitation for younger adults and more than 1 trillion people-hours for older adults every year due to extreme heat conditions. These restrictions occur when temperatures and humidity levels become so intense that even light outdoor activity becomes unsafe.
The research highlights that the worst-affected regions include the Indo‑Gangetic Plain and the eastern lowlands of the country. In contrast, elevated regions such as the Western Ghats and the Himalayan foothills experience relatively lower levels of heat stress.
Scientists describe these conditions as severe “livability limitations,” where heat stress restricts normal daily activity. In the most extreme cases, temperatures can create conditions classified as “unlivable,” meaning even resting outdoors becomes extremely uncomfortable and potentially dangerous, though not necessarily fatal.
According to the study, about 35 percent of the world’s population lives in areas where outdoor livability is limited for younger adults, while 78 percent live in regions where older adults face such limitations.
The findings also show that the elderly population is much more vulnerable to heat stress. Older adults now experience around 900 hours per year of severe heat limitation, compared with about 600 hours per year during the 1950s. This means that for nearly 10 percent of the year, it may be unsafe for elderly people to perform even light outdoor activities.
Researchers explain that the difference occurs because aging reduces the body’s ability to regulate temperature. Older adults sweat less efficiently and have more difficulty cooling their bodies during hot and humid conditions.
The study also found that coping strategies can vary with age. For instance, simple cooling methods such as hand-held fans may not always help older adults in extremely hot and dry conditions because they can reduce the body’s natural sweating ability.
To measure heat stress, scientists used a model called HEAT-Lim which estimates how much activity a person can safely perform without their core body temperature rising to dangerous levels. The model incorporates climate conditions, age-related physiological limits, and humidity levels to map heat-related livability across the world.
The research is based on climate risk frameworks developed by the Intergovernmental Panel on Climate Change and was published in the scientific journal Environmental Research: Health.
Experts say extreme heat is also widening social inequalities. Poor communities often face greater heat exposure because they work outdoors in sectors such as construction, agriculture, and street vending. Unlike wealthier populations, they have limited access to cooling systems like air conditioners or the ability to remain indoors during heatwaves.
The study also notes that its findings may underestimate the real risk because the calculations assume people are in shaded conditions with calm air. Workers exposed to direct sunlight such as farmers and laborers may face even higher heat stress.
Researchers warn that the current increases in heat-related livability limitations have occurred with just about 1°C of global warming. With temperatures expected to rise further and populations aging worldwide, a much larger share of people could face severe heat limitations in the future unless strong climate mitigation and adaptation measures are implemented.