At an intense level of combined heat and humidity—a “wet bulb” reading of 35 degrees Celsius, hotter and more humid than humans have ever experienced—the air will become so muggy that people can’t sweat and their organs begin to shut down. A healthy person sitting outside could eventually overheat and die, even if they’re resting in the shade. And by 2030, there’s a chance that this type of deadly heat wave could hit regions in India where as many as 200 million people live.
