The number of people worldwide struggling with extreme heat and humidity by the end of the century could be more than four times as many as today if planet-warming emissions continue to rise, hiking economic losses and health costs, scientists have warned. Spending on mental health, in particular, could soar as more families have trouble sleeping and working, and heat aggravates existing mental health problems, one of two new studies found. "Heat and humidity extremes have real impacts on health and productivity," said Bob Kopp, director of the Institute of Earth, Ocean & Atmospheric Sciences at Rutgers University, and an...