A new study published in Nature Sustainability warns that the number of people exposed to extreme heat will more than double by 2050 if global temperatures rise by 2C above pre-industrial levels. The research, which is the most detailed analysis of its kind, projects that 41% of the world's population—around 3.79 billion people—will face extreme heat days annually, up from 23% in 2010.
The study defines extreme heat as days where temperatures deviate significantly from a temperate baseline of 18C. Using computer models, the authors mapped the regions most affected. The majority of those impacted will be in India, Nigeria, Indonesia, Bangladesh, Pakistan and the Philippines, but the most significant increases in dangerous temperatures will occur in Central African Republic, Nigeria, South Sudan, Laos and Brazil.
No region will be immune, the authors say. While the tropics and southern hemisphere will be worst affected, northern countries will also struggle because their built environments are designed for cooler climates. In the UK, for example, old and inefficient buildings and infrastructure pose challenges to health systems, energy supplies and the economy during heatwaves. In 2023, the National Grid had to fire up two coal-fired power plant units to meet air conditioner demand during an unusual heatwave.
The study also found that the greatest shift in extreme heat will occur early in the warming trajectory, near the 1.5C phase, adding urgency to adaptation measures. Co-author Radhika Khosla of Oxford University said: “This is a really core finding because it tells us that we need to act much earlier in supporting measures for adaptation and mitigation. Overshooting 1.5C of warming will have an unprecedented impact on everything from education and health to migration and farming.”
The research highlights that energy demand for cooling will far outstrip heating by the end of the century, as the northern hemisphere's heating bill decreases while the southern hemisphere's cooling bill increases. Khosla stressed that net zero sustainable development remains the only established path to reversing the trend for ever hotter days.
