Within 50 years, one-third of the earth’s population could be living in a climate that is hotter than what is currently found on 99% of the Earth’s land surface, according to a new report in the Proceedings of the National Academy of the Arts and Sciences.
The regions most likely to be affected are among the world’s poorest, the report said. India, and large parts of Africa, East Asia, the Middle East, and South America are projected to be affected by this extreme heat.
"Our core result is what you could call a sensitivity of humanity to warming," Marten Scheffer, one of the study’s authors and a professor of complex systems sciences at Wageningen University in the Netherlands, told the New York Times.
In other words, the health risks of this temperature increase are grave.
The report found that for thousands and thousands of years, humans have resided in a narrow climate range, with a mean annual temperature (MAT) of around 11 to 15 degrees Celsius (51.8 to 59 degrees Fahrenheit) .
"It turns out that the preference of humans has been really consistent," Scheffer told the New York Times. "The vast majority of people [have] always been concentrated in a small range of conditions."
Yet with no climate change mitigation or migration, 3.5 billion people could be living in a climate with a MAT at, or equal to, 29 degrees Celsius (84.2 degrees Fahrenheit) by 2070. This is in part because regions of the world that are already quite hot are experiencing major population growth.
Currently, 0.8% of the Earth’s land, primarily in the Sahara, experiences a MAT at, or equal to, 29 degrees Celsius, but 19% of global land is projected to reach that MAT by 2070.
Even with "strong climate mitigation," 1.5 billion people could be living in extreme heat conditions, well outside the human comfort range.
"I think it is fair to say that average temperatures over [29 degrees] are unliveable. You’d have to move or adapt," Scheffer told the Guardian.
"But there are limits to adaptation. If you have enough money and energy, you can use air conditioning and fly in food, and then you might be OK. But that is not the case for most people," he added.
For the billions of people who might live in extreme heat, activities such as growing food will become more difficult, potentially increasing poverty.
The authors found that other regions could become more hospitable, further driving global migration trends.
Nevertheless, the possibility that hundreds of millions of people will have to migrate in the coming decades due to climate change means that the public "needs to think about how we can accommodate as much as we can," Scheffer told the New York Times.