Extreme heat: Nearly 3.8 billion people could be living with extreme heat exposure by mid-century, according to a new study that warns the demand for cooling will surge not only in tropical nations but also in countries historically shaped by cold weather.
Researchers at the University of Oxford said the biggest strain will fall on tropical and equatorial regions, where hotter days are expected to multiply, and large parts of the population still lack reliable access to air conditioning or even basic cooling. They pointed to major countries such as Brazil, Indonesia and Nigeria, where rising temperatures could drive a sharp jump in energy demand for cooling.
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But the study also cautions that even modest warming could hit cooler regions hard, because homes, cities and public transport systems there are often not built for heat. Countries such as Canada, Russia and Finland may face “severe” impacts from a rise in hot days, the researchers said, despite currently experiencing fewer extreme-heat events than tropical nations.
The findings, published in Nature Sustainability, modelled how often people could experience temperatures considered uncomfortably hot or cold under different warming scenarios. Under a world that is 2°C warmer than pre-industrial levels, the researchers estimate the number of people exposed to extreme heat would almost double by 2050, reaching about 3.79 billion.
Lead author Jesus Lizana said much of the impact could arrive sooner than many governments assume, as the world approaches the 1.5°C warming threshold. “The need for adaptation to extreme heat is more urgent than previously known,” he said, calling for new infrastructure, such as energy-efficient air conditioning and passive cooling solutions, to be deployed quickly.
Health experts have long warned that sustained exposure to high temperatures can overwhelm the body’s ability to cool itself, increasing the risk of dehydration and heat exhaustion and, in severe cases, organ failure and death. Heat is often described as a “silent killer” because fatalities can occur after prolonged strain rather than during a single dramatic event.
The study highlights a widening gap in preparedness. It projects the steepest increase in “cooling degree days”, a measure of how often temperatures are high enough to require cooling, in many tropical and African countries. The Central African Republic, Nigeria, South Sudan, Laos and Brazil were among the places expected to see the biggest rises in dangerously hot conditions.
Urban climate scientist and co-author Radhika Khosla said the burden will fall disproportionately on those least able to adapt. “The most disadvantaged people are the ones who will bear the brunt of this trend,” she said.
At the same time, the researchers said wealthier countries should not assume they are insulated. Under a 2°C scenario, some colder nations could see a significant drop in “heating degree days,” potentially reducing heating needs. But Lizana said those savings may be offset over time by rising cooling costs—particularly in parts of Europe, where air conditioning remains relatively uncommon.
“Wealthier countries cannot sit back and assume they will be OK,” Lizana said, warning that many are “dangerously underprepared” for the heat expected over the coming years.
