Heat-related deaths in U.S. far exceed official tallies, NPR-BU investigation finds

The Centers for Disease Control and Prevention (CDC) compiles the official tally of heat-related deaths from state reports. From 2004 to 2018, that annual number averaged around 700. In recent years, it has crept up to an average of 1,700, sometimes topping 2,000. But the NPR-BU analysis estimates that between 2018 and 2025, about 9,000 deaths each year were influenced by heat, with some years exceeding 10,000.

Quinn Adams, a research scientist at Boston University's Center for Climate and Health, said the true figure could be even higher because of limitations in the data and the conservative nature of the analysis. Heat dangers are growing every year due to human-caused climate change. The heat wave season has extended by a month and a half since the 1960s, and the number of heat waves in 50 of the country's largest cities has doubled since the 1980s.

Dr. Sameed Khatana of the University of Pennsylvania's Perelman School of Medicine explained that heat is often a hidden factor in deaths. "Heat is what people often call the silent killer," he said. Heat can trigger a heart attack by making the heart work harder to cool the body. Because heat leaves no obvious mark on the body, death certificates often list only the immediate cause, such as a heart attack, and omit heat. These omissions, repeated thousands of times, create a blind spot that obscures the scale of heat's danger.

The investigation also found that heat is killing people in nearly every corner of the country. The full analysis will soon be published in a scientific journal.