A new study from the University of Oxford has found that nearly 3.8 billion people worldwide could face extreme heat by 2050, highlighting a climate threat that will hit tropical nations hardest while also affecting traditionally cooler regions, the researchers said on Monday.
Scientists warned that countries such as Brazil, Indonesia and Nigeria will see dramatic increases in the need for cooling, as hundreds of millions of residents currently lack access to air conditioning or other methods to escape soaring temperatures. The study, published in the journal Nature Sustainability, projects that the population experiencing extreme heat conditions could nearly double by mid-century if global average temperatures rise 2 degrees Celsius above preindustrial levels.
But researchers said the most significant impacts could arrive much sooner, within the next decade, as the world approaches the 1.5-degree threshold. “The key takeaway from this is that the need for adaptation to extreme heat is more urgent than previously known,” said lead author Jesus Lizana, an environmental scientist. He stressed that new infrastructure—such as sustainable air conditioning or passive cooling systems—must be deployed rapidly to prevent dangerous health consequences.
Prolonged exposure to extreme heat can overwhelm the body’s natural cooling systems, leading to symptoms that range from dizziness and headaches to organ failure and death. Often described as a “silent killer,” heat-related fatalities can occur gradually as high temperatures and environmental stress combine to disrupt the body’s internal thermostat. Climate change is already lengthening and intensifying heatwaves, and the study indicates that access to cooling will become increasingly essential.
The research also forecasts that the biggest rises in “cooling degree days”—temperatures high enough to require cooling—will occur in tropical and equatorial countries, especially across Africa. The Central African Republic, Nigeria, South Sudan, Laos and Brazil were identified as the regions facing the most significant increases in dangerously hot conditions. India, the Philippines and Bangladesh are also expected to see some of the largest affected populations, with substantial health risks and energy demand increases in developing nations.
Researchers emphasized that the burden will fall most heavily on disadvantaged populations. “Put simply, the most disadvantaged people are the ones who will bear the brunt of this trend,” said urban climate scientist and co-author Radhika Khosla.
However, the study also sounded an alarm for wealthier countries in cooler climates that may not yet recognize the scale of the problem. Nations such as Canada, Russia and Finland could experience sharp drops in “heating degree days,” but even moderate increases in hot temperatures would be particularly disruptive in places where infrastructure is not built for heat. Buildings in colder regions are typically designed to maximize warmth and minimize ventilation, and public transport systems often operate without air conditioning. While some countries may see short-term savings on heating bills, those gains are likely to be offset by rising cooling costs over time, especially in Europe where air conditioning remains uncommon.
“Wealthier countries cannot sit back and assume they will be OK,” Lizana said. “In many cases they are dangerously underprepared for the heat that is coming over the next few years.”
