 USA Today looked at the hidden cost of staying cool during heat waves. Number one, extreme heat is the leading cause of weather-related deaths, with more than 1,200 people dying every year. Number two, three years ago, more than 2.5 billion hours of labor were lost due to heat exposure in the agriculture, construction, manufacturing, and service sectors. A separate report found that health care costs from extreme heat amount to an estimated $1 billion every summer.