Heat waves can kill people, and by 2100, half of Earth’s population could experience 20 days or more of life-threatening heat every year. And that’s if humans drastically reduce their CO2 footprint. In the worst-case scenario — if greenhouse gas emissions keep growing — some 75 percent of humans could feel that deadly heat, according to a June paper published in Nature Climate Change.
The research team, led by University of Hawaii scientists, analyzed future climate trends by looking at studies of past heat waves. They found that combinations of heat and humidity exceeding our ability to cool ourselves with sweat could regularly threaten large swaths of humanity by 2100.
What’s more, the analysis indicates that many regions near the tropics in particular — where billions of people live — would experience conditions regularly exceeding that limit, making the areas effectively uninhabitable.