As the planet warms, more of Earth’s surface is edging toward temperatures that even the healthiest humans cannot endure. A new study, led by scientists at King’s College London, warns that a mere half-degree increase in global warming could triple the area of land where extreme heat becomes unsurvivable.
This means we’ll have more places like Kuwait City and Doha, which routinely face blistering summers with mercury levels soaring above 50°C.
It’s a grim picture of a future where vast swaths of the planet — areas the size of the United States — could become too hot for human life. At 2°C above preindustrial levels, six percent of Earth’s landmass would exceed a threshold such that even young, healthy adults could no longer maintain a safe core body temperature.
For those over 60, the risk is even more dire: more than a third of the planet’s land could cross the critical ‘overheating’ threshold.
“Our findings show the potentially deadly consequences if global warming reaches 2°C,” said Dr. Tom Matthews, the study’s lead author and a senior lecturer in environmental geography at King’s College London.
Fewer places to hide from impending global heating
The human body is remarkably resilient, but it has its limits. When the combination of heat and humidity — measured as “wet-bulb temperature” — exceeds 35°C (95°F), the body can no longer cool itself through sweating. This is the “uncompensable” threshold, where the human core body temperature begins to rise uncontrollably. If it reaches 42°C (107.6°F) within six hours, a person risks heatstroke, organ failure, and even death. The older you are, the higher the risk.
Between 1994 and 2023, about 2% of the planet’s land area breached this threshold for adults under 60. For older adults, more than 20% of the Earth’s surface crossed this line. But as temperatures climb, these thresholds will be crossed more frequently — and by more people.
“Unsurvivable heat thresholds, which so far have only been exceeded briefly for older adults in the hottest regions on Earth, are likely to emerge even for younger adults,” Matthews explained. “In such conditions, prolonged outdoor exposure—even in the shade, with a strong breeze, and while well hydrated—would be expected to cause lethal heatstroke.”
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The study also projects what would happen if warming reaches 4-5°C above preindustrial levels, a scenario that could unfold if greenhouse gas emissions continue unabated by the end of this century. At this level, 60% of the Earth’s land surface could become uninhabitable for older adults during extreme heat events. Younger adults in subtropical regions would also begin to face unsurvivable conditions.
The deeper implications
The implications are staggering. Regions like Saharan Africa and South Asia, already prone to extreme heat, would bear the brunt of this crisis. But no continent would be spared. The study underscores the urgent need for both mitigation and adaptation.
“Anticipating the magnitude of future heat extremes and their worst-case impacts is critical to understanding the costs of failing to mitigate climate change,” Matthews said. “It is also crucial for targeting adaptation efforts at those communities most in need.”
“What our review really shows very clearly is that, particularly for higher levels of warming such as 4°C above the pre-industrial average, the health impacts of extreme heat could be extremely bad,” he added.
Heat is already a silent killer. Since 2000, more than 260,000 people have died in the deadliest heat events. The European heatwaves of 2003 and 2022, along with the Russian heatwave of 2010, collectively claimed nearly 200,000 lives.
We’re at a critical stage
The study is a stark reminder that the fight against climate change is not just about saving wildlife or preserving ice caps — it’s also about saving ourselves.
The solution has always been straightforward: slashing emissions to prevent the worst-case scenarios and helping communities adapt to the heat that is already inevitable. Reliable access to cooler environments, better urban planning, and early warning systems could save countless lives.
But time is running out. Last year was the first on record with a global mean temperature more than 1.5°C above preindustrial levels. At current rates of warming, the 2°C threshold could be breached by mid-century.
According to the Global Carbon Project, global CO2 emissions probably rose by 0.8% in 2024, amounting to a record 37.4 billion tons of CO2. The report warns carbon budgets to limit warming to 1.7°C and 2°C would similarly be used up in 15 and 27 years, respectively.
The findings appeared in the journal Nature Reviews Earth and Environment.
