Warming threatens to expand area of world too hot for humans

Extreme heat could reach lethal levels across an area equivalent to the size of the United States if global temperatures rise 2°C above pre-industrial levels, scientists warned Tuesday.

A study published in Nature Reviews Earth and Environment found that climate-driven heatwaves are increasingly pushing human endurance to the limit, with North Africa and South Asia most at risk.

Between 1994 and 2023, unsafe heat and humidity conditions covered 2% of global land for adults under 60. But at 2°C warming, that area could triple—exposing billions to dangerous heat levels.

For people over 60, the affected area could expand to one-third of the planet’s landmass.

“In such conditions, even those in the shade with a breeze and proper hydration would face lethal heatstroke,” said Tom Matthews, the study’s lead author from King’s College London.

Deadly heatwaves have killed tens of thousands across the world. In Saudi Arabia’s 2023 hajj pilgrimage, over 1,300 people died as temperatures soared to 51.8°C (125°F). Europe has suffered over 70,000 deaths in a single summer, with heatwaves in India and Pakistan killing thousands.

Yet, deaths in Africa remain severely underreported, researchers noted. The World Health Organization estimates heat kills at least 500,000 people annually—but the real number could be 30 times higher.

The Paris Agreement aims to limit warming to 1.5°C, but 2023 already surpassed that threshold for the first time. Scientists warn that exceeding 2°C could bring irreversible climate impacts—with deadly heat expanding rapidly across the planet.