A 2°C increase in global temperatures could make six percent of the Earth’s land—an area roughly the size of the United States—so hot that even healthy adults would struggle to maintain a safe body temperature, warns a new study in the journal Nature Reviews Earth and Environment.
This would mark a tripling of the landmass where healthy individuals aged 18 to 60 would cross the “critical overheating threshold” during extreme heat events. The outlook is worse for people aged over 60, with overwhelming heat expected across 35% of land during heat events.
Unsurvivable heat thresholds—when lethal core body temperatures increase within six hours—have thus far been exceeded only briefly for older adults in the hottest parts of the planet, lead author Tom Matthews, a senior lecturer of environmental geography at King’s College London, said in a news release. But at warming of 2°C above pre-industrial levels, the study finds, the thresholds are “likely to emerge even for younger adults.”
“Potentially deadly consequences” will ensue: “In such conditions, prolonged outdoor exposure—even for those in the shade, subject to a strong breeze, and well hydrated—would be expected to cause lethal heat stroke.”
The findings represent “a step-change in heat-mortality risk,” Matthews added.
Global mean temperature exceeded 1.5°C over the course of 2024, with long-term averages approaching that milestone, according to the United Nations Environment Programme. The Earth is on track for 2.6°C to 3.1°C of warming by the end of the century. Projected increases in extreme temperatures are “a fundamental concern for human health,” the study authors write, noting that between 2003 and 2020, nearly 200,000 people died during three extreme heat events in Europe and Russia.
Already by 2020, extreme heat events that were once rare—expected only once in a century—were five to 10 times as frequent as they were in 2000. At 2°C of global warming, they could occur every few years.
South Asia and western Africa are at greatest risk, their vulnerability compounded by a dearth of heat morbidity data.
Given the rapid pace at which warming threatens to “overwhelm human physiology,” reliable, universal access to cool refuges is “an urgent priority,” the researchers write.
Access options for sustainable, affordable, and resilient cooling include air conditioning powered by renewable microgrids and passive cooling techniques incorporated into building design.
“Limiting anthropogenic warming remains the most sound strategy for avoiding the most severe heat events,” they write.
The heat mortality study was published shortly after temperatures at the North Pole reached 0.5°C, more than 20°C above the seasonal average. The temperature spike, which caused ice at the top of the world to begin melting, is being linked to a “deep low-pressure system over Iceland, which was directing a strong flow of warm air towards the North Pole,” reports the Guardian. “Extra-hot seas” in the northeast Atlantic are also involved.
“This was a very extreme winter warming event,” said climate scientist Mika Rantanen of the Finnish Meteorological Institute. “Probably not the most extreme ever observed, but still at the upper edge of what can happen in the Arctic.”
“The Arctic has warmed nearly four times faster than the global average since 1979, and extreme heat has become hotter and more common,” reports the UK news outlet.
