Nearly 3.8 billion people worldwide could be exposed to extreme heat by 2050, with tropical countries bearing the brunt but cooler regions also facing serious challenges, scientists have warned.
Researchers from the University of Oxford say demand for cooling will “drastically” increase in major countries such as Brazil, Indonesia and Nigeria, where hundreds of millions of people currently lack access to air conditioning or other effective cooling systems.
However, even traditionally cooler nations like Canada, Russia and Finland could experience severe impacts from a moderate rise in hot days, the scientists cautioned.
The findings, published in the journal Nature Sustainability, are based on projections under different global warming scenarios. The researchers examined how often people might experience temperatures considered uncomfortably hot or cold in the future.
They found that the number of people exposed to extreme heat conditions is expected to nearly double by mid-century if global average temperatures rise 2°C above preindustrial levels. Under this scenario, about 3.79 billion people could be affected.
But the most significant impacts are expected much sooner. Lead author Jesus Lizana said most of the change would be felt this decade as the world approaches the 1.5°C warming threshold.
“The key takeaway is that the need for adaptation to extreme heat is more urgent than previously known,” Lizana said.
“New infrastructure, such as sustainable air conditioning or passive cooling, needs to be built within the next few years to ensure people can cope with dangerous heat.”
Prolonged exposure to extreme heat can overwhelm the body’s natural cooling systems, leading to symptoms ranging from dizziness and headaches to organ failure and death. Heat is often described as a “silent killer” because most heat-related deaths occur gradually as high temperatures and environmental factors combine to strain the body.
The study found that the sharpest increases in “cooling degree days” temperatures hot enough to require cooling through air conditioning or fans would occur in tropical and equatorial regions, particularly in Africa.
Countries such as the Central African Republic, Nigeria, South Sudan, Laos and Brazil are projected to see the largest rise in dangerously hot temperatures. India, the Philippines and Bangladesh would also be among the most affected, with major public health consequences.
“Put simply, the most disadvantaged people are the ones who will bear the brunt of this trend toward ever hotter days,” said co-author Radhika Khosla, an urban climate scientist.
But wealthier countries in cooler climates are not off the hook.
“These countries also face a major problem even if many do not realise it yet,” Khosla said.
Under a 2°C warming scenario, countries like Canada, Russia and Finland may see significant declines in “heating degree days,” meaning fewer cold days that require indoor heating. While this could lower heating bills in the short term, Lizana said those savings would likely be offset by rising cooling costs over time.
In Europe, where air conditioning is still relatively uncommon, demand for cooling is also expected to grow sharply.
“Wealthier countries cannot sit back and assume they will be OK in many cases they are dangerously underprepared for the heat that is coming over the next few years,” Lizana warned.
The researchers say urgent investment in heat-resilient infrastructure and accessible cooling solutions will be essential to protect billions of people from escalating climate risks.