Heat waves are America's deadliest weather disaster.

A man wipes sweat from his face July 10, 2007 in New York City. New York City is experiencing a second day of a heat wave with temperatures in the upper 90`s and uncomfortable humidity levels.

Heat waves are quickly becoming one of the world’s deadliest weather phenomena. In the United States, extreme heat now kills more people each year than tornadoes, hurricanes, or flooding. And a massive heat wave, like the one that hit Europe in 2003, can kill tens of thousands in a blow.