Rising heat exposure driven by climate change could place billions of people in densely populated countries at heightened risk by mid-century, according to a major new assessment led by researchers at the University of Oxford. The findings underscore how escalating global temperatures, combined with urbanisation and demographic pressures, are likely to push heat stress beyond levels that public health systems and economies are prepared to manage.The study projects that by 2050, large parts of South Asia, Africa and the Middle East will experience a sharp increase in the number of days each year when temperatures and humidity reach thresholds considered dangerous for human health. Countries with high population density and extensive outdoor labour are expected to bear a disproportionate share of the burden, with India highlighted as one of the most exposed due to its climate, scale and socio-economic profile.
Researchers examined long-term climate models alongside population and land-use data to estimate how many people could be exposed to extreme heat under different warming scenarios. Even under pathways that assume significant emissions reductions, the analysis shows a substantial rise in heat exposure compared with present conditions. Under higher-emissions trajectories, the increase becomes markedly steeper, with some regions facing heat conditions that were previously rare or unknown.
Heat exposure is not defined by temperature alone. The study places particular emphasis on so-called “wet-bulb” temperatures, which combine heat and humidity and offer a more accurate measure of the stress placed on the human body. When wet-bulb temperatures exceed certain levels, the body’s ability to cool itself through sweating is impaired, raising the risk of heat exhaustion, heatstroke and, in extreme cases, death. The Oxford-led team warns that such thresholds could be crossed more frequently across the Indo-Gangetic plain and other densely inhabited regions.
India’s vulnerability is compounded by rapid urban growth and the expansion of heat-absorbing infrastructure. Large cities with limited green cover and high concentrations of concrete and asphalt are already experiencing pronounced urban heat island effects. The study suggests that without significant adaptation measures, these effects could amplify climate-driven warming, pushing peak temperatures in cities several degrees higher than in surrounding rural areas.
Public health implications feature prominently in the analysis. Rising heat exposure is associated with increased mortality, particularly among older people, children and those with pre-existing health conditions. Outdoor workers in construction, agriculture and informal sectors face elevated risks, with heat stress linked to reduced productivity, higher accident rates and long-term health damage. The study estimates that economic losses from heat-related productivity declines could run into hundreds of billions of dollars globally by 2050, with South Asia accounting for a large share.
The research also highlights unequal impacts within countries. Low-income households, often living in poorly ventilated housing and lacking access to cooling, are expected to be more exposed than wealthier populations. Rural communities dependent on rain-fed agriculture may face simultaneous pressures from heat stress and declining crop yields, increasing the risk of food insecurity and migration.
While the findings paint a stark picture, the authors stress that outcomes are not predetermined. Adaptation measures such as heat-resilient urban design, expanded green spaces, early warning systems and improved access to healthcare can significantly reduce risks. The study points to examples where targeted heat action plans, including public cooling centres and modified working hours during heatwaves, have already lowered heat-related mortality.
Mitigation remains central to limiting long-term exposure. The analysis makes clear that the scale of future heat risk is closely tied to global emissions pathways. Lower warming scenarios consistently result in fewer people exposed to dangerous heat levels, reinforcing the importance of rapid reductions in greenhouse gas emissions alongside local adaptation efforts.
The report has been released amid a growing body of evidence linking climate change to more frequent and intense heat events worldwide. Meteorological records over the past decade show a steady rise in average temperatures and an increase in prolonged heatwaves across multiple continents. Against this backdrop, the Oxford study adds a forward-looking dimension, quantifying how demographic and climatic trends may intersect over the coming decades.