“We know that climate change is making extreme heat and humidity more common,” said Robert Kopp, a climate scientist at Rutgers University. “And both of those things reduce our ability to live in a given climate.” Dr. Kopp, who was an author of a study published last year that found that exposure to heat and humidity extremes was increasing worldwide, said a key contribution of the new work was in showing that, for the tropics, “it is easier to predict the combined effects of heat and humidity than just how hot it is.”