If (when) the planet reaches two degrees Celsius of warming, the options of where humans can live will be quite a bit smaller. A study published on Tuesday found that an extra USA-sized chunk of the world may at times be too hot for human habitation, a jump from just two percent of the landmass today up to six percent.
“Our findings show the potentially deadly consequences if global warming reaches 2°C,” said Tom Matthews, a senior lecturer at King’s College London, who led the new study, in a press release. “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.”
The researchers mixed climate modeling with research on human survivability thresholds for heat and humidity, known as wet bulb temperatures. They found that for the period from 1994 through 2023, just 2.2 percent of the world’s land area crossed “uncompensable” thresholds — beyond which core body temperatures rise uncontrollably —for young (18 to 60 years), healthy people. “Unsurvivable” thresholds, where core temperatures reach a lethal point within six hours, have only so far really been breached for extended periods for older adults. At an average of two degrees of warming, though, that uncompensable percentage triples.
Last year the world saw an average temperature above 1.5 degrees C of warming for the first time; we will need years above that line before scientists would say the world has officially warmed beyond that Paris Agreement target, but it’s clearly not all that far off. Current policies around the world still have us on track for around 2.7 degrees of warming in total. The new study, published in Nature Reviews Earth & Environment, found that at the high end of projected possibilities, in the four to five degrees range, an incomprehensible 60 percent of the land mass could pass uncompensable levels during extreme heat events. Those high-end scenarios have decreased in likelihood in recent years, but the world is not exactly acing its climate policy tests these days, so who knows.
“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,” Matthews said.
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