Exceeding human heat tolerance in a warming, ageing world: a global projection modelling study

This global modelling study examines how climate change and population ageing interact to increase exposure to uncompensable heat stress, conditions under which the human body can no longer maintain thermal balance. Unlike previous studies that applied heat tolerance thresholds developed for young adults to all age groups, the authors integrate experimentally derived heat limits for young, middle-aged, and older adults with climate and demographic projections.

The findings show that older adults face substantially greater and earlier exposure to dangerous heat than previously estimated. Under 1.5°C of global warming, older adults are projected to experience more frequent and widespread heat tolerance exceedances than young adults would under 4°C of warming. South Asia and the Persian Gulf emerge as major hotspots, where older adults could face sustained day-and-night exposure for months under higher warming scenarios. The study highlights the need for age-sensitive heat adaptation policies, targeted heat action plans, cooling infrastructure, and stronger support for vulnerable populations. It also underscores the importance of climate mitigation to limit future exposure to intolerable heat.