NPR estimates that heat-related mortality in the United States is about five times the official count

NPR estimates that heat-related mortality in the United States is about five times the official count

On August 31, NPR published a joint estimate with the Boston University Center for Climate and Health. For 2018–2025, the model attributed an average of about 9 thousand deaths per year to heat. Over the same period, death certificates identified heat exposure in about 1.7 thousand cases per year.

These methods measure mortality differently. The federal CDC WONDER cause-of-death registry records what was entered on the death certificate: one underlying cause and any contributing causes. Heat makes the heart beat faster and work harder to direct blood toward the skin. In a person with heart disease, this strain can cause a heart attack, which may be recorded on the death certificate as the immediate cause of death.

“Heat is often called a silent killer, unlike hurricanes and typhoons,” says Samed Khatana, a physician at the University of Pennsylvania’s Perelman School of Medicine.

For the analysis, the researchers used weekly all-cause mortality data from 530 counties with populations of at least 50 thousand, covering about 73% of the US population. They compared each week’s temperature, as well as the temperature in the following week, with the number of deaths recorded in 2018–2025, excluding 2020. They assessed temperature relative to the usual climate of each county, then identified, at the state level, the temperature at which the model predicted the lowest mortality. This approach accounted for the fact that the same level of heat can have different effects in places with different climates.

After estimating the number for each county, the authors added the estimates together and extrapolated the result to the continental United States. This produced a national estimate of about 9 thousand deaths per year statistically associated with temperatures above that level.

In Maricopa County, which includes Phoenix, death investigators already ask about access to air conditioning, electricity bills, and medications that increase sensitivity to heat. The national analysis looks for the same association in weekly temperature and all-cause mortality data, producing an estimate of about 9 thousand deaths per year. The method used to count heat-related deaths determines which risks are addressed through prevention.