A study highlights that India faces severe limitations on daily activities due to extreme heat, affecting both younger and older adults.
The Indo-Gangetic Plain and eastern lowlands are particularly impacted.
India sees 100 billion people-hours of limitation for younger adults and over 1 trillion people-hours of limitation for older adults.
This exacerbates inequality, as poorer populations are less able to adapt.
Heat stress due to anthropogenic global warming is increasingly being recognised as a major global health challenge and one that disproportionately affects the poor. A new heat sensitivity-based liveability study on different age groups across the world revealed that the number of hours people can be outdoors safely and comfortably has shrunk in hot areas since the mid-century, thus reducing livability.
About 35 per cent of the global population live in places where livability is restricted for younger adults and 78 per cent live in areas with limited livability for the elderly population, the findings showed.
The analysis also showed that some of the most populous areas on the Earth experience severe livability limitations, with India showing the highest magnitude of overlap. As a result, the country records around a 100 billion people-hours of limitation and over 1 trillion people-hours of limitation for older adults.
The researchers noted that increase in livability limitations clashed with the presence of El Nino, except for 2024 where significant spikes were observed although strong El Nino was absent during most of the year.
The condition where no activity (even sitting or lying down) is possible due to heat stress, but is potentially survivable, has been categorised as 'unlivable' by the analysts. Although this means heat stress would be unbearable even during rest, the condition is not necessarily lethal, they added.
In India, the Indo-Gangetic Plain and eastern lowlands experienced these conditions at some point or the other during 1995-2024. The elevated regions in the Western Ghats and Himalayan foothills have significantly lower severity of limitations.
In fact the entire South Asia region is among those with the around a third or half the year (1,500-2,000 hours per year) with severe livability limitations. Other regions with this severity include tropical South America, the tropical Atlantic, tropical western sub-Saharan Africa, and Southwest and East Asia.
When the study was conducted, some 24.5 per cent of the global population were found to be residing at locations considered unlivable for older adults and 1 per cent in places unlivable for younger adults, the researchers wrote in the report.
The heat limitation is many times more pronouced for the elderly population, who experience an average of 900 hours every year when their livability is severely limited, according to the report Intensifying global heat threatens livability for younger and older adults published in Environmental Research: Health on March 10, 2026. This has gone up from 600 hours in a year during the 1950s.
This means, for about 10 per cent of the year, it is unsafe for the old to perform even light activity outdoor because of extreme heat, increasing their dependability.
This is particularly the case because physiologically, older adults cannot thermoregulate or cool themselves through sweating as efficiently as younger people under similar ambient temperature and humidity, the researchers explained.
Even individual ways to cope with this heat, such as using small, hand-held fans to increase air movement, differred according to the age group, according to the scientists. In extremely hot and dry environments, it can lower sweating ability of older adults, thus not letting their bodies cool down naturally.
The researchers used a biophysical approach based on a human heat balance model to measure the level of activity a person can perform safely without an uncontrollable rise in their core body temperature. Based on this understanding, they mapped areas where livability is limited.
The model, named HEAT-Lim, was built on the Intergovernmental Panel on Climate Change Assessment Report 5 Working Group II climate risk framework. It is more nuanced than other existing heat stress metrics that don't consider age and sweating limits along with climate conditions.
The authors highligted how this condition is widening inequality among and within countries. Low-income regions are more heatwave-prone and are projected to see higher heatwave exposure in the future than high-income regions, the analysis showed. Further, socioeconomic vulnerabilities add a further layer to the disparity, with the wealthy in a better position to adapt to these circumstances by staying indoors or using air conditioners, while for the poor, especially outdoor workers, it either means heightened heat risk or lower income due to reduced work hours.
The real impact is probably much higher for people who have to face direct sun, such as labourers and farmers, because the study is based on exposure in the shade and with calm air flow during the hottest hours of the year.
The reported increases in livability limitations were observed with just over 1°C of global warming, the researchers highlighted. With a global ageing population and projected increase in warming without urgent measures, a significantly larger share of people will face severe livability limitation in the coming days, they warned.