The U.S. Environmental Protection Agency calls heat “the leading weather-related killer in the United States.” On average, it kills about 600 Americans every summer — a number that's expected to rise as climate change fuels more extreme heat waves. Yet, even as heat becomes a bigger problem that garners more public attention, experts say that many cities and states across the country greatly underestimate the number of people who die annually from extreme heat. | WBUR 90.9 FM