text:  It's barely summertime, but nearly every part of the U.S. has already experienced heat that's dangerous to people's health. Alejandra Porunda with NPR's Climate Desk tells us about one tool that can help emergency rooms and health professionals prepare. When temperatures rise, emergency physician Anish Narang knows what to expect. Every summer now, especially the last three or four years, it's staggering. He works at Banner University Medical Center in Phoenix, Arizona. It's one of the hottest cities in the country.