An investigation by NPR in partnership with Boston University has determined that heat contributes to far more deaths across the United States than government statistics indicate. The project examined mortality data from hundreds of counties and developed a statistical model to estimate heat's broader influence.
Between 2018 and 2025, the analysis placed the annual average at approximately 9,000 heat-influenced deaths. This figure is roughly five times higher than the average reported by the Centers for Disease Control and Prevention over the same span.
Official counts rely on death certificates that list heat exposure as a primary or contributing factor. Researchers note that heat often goes unrecorded because it accelerates existing conditions such as heart disease without leaving clear physical evidence for medical examiners.
The model showed elevated risks in many states not traditionally viewed as hot. Michigan recorded more than 100 such deaths yearly compared with roughly 10 in official data, while Massachusetts estimates reached over 60 versus about five reported.
Florida and Texas led in total numbers, partly due to population size, yet the pattern extended nationwide. The study also highlighted that air conditioning coverage remains uneven, leaving residents in states like Washington and Maine more exposed as heat events increase.
Maricopa County in Arizona has implemented detailed review protocols that capture more cases, including checks on cooling systems and medication use. Most other areas lack comparable procedures, resulting in persistent undercounts.
Experts involved in the project stressed that improved tracking is essential for targeted prevention as climate change extends heat wave seasons and raises peak temperatures in additional regions.
This report is based on coverage by LAist: https://laist.com/news/climate-environment/tracking-deaths-from-heat-staggering-hidden-toll