NPR and Boston University spent two years analyzing mortality data across the country and found that roughly 9,000 Americans die annually from heat-related causes — five times the CDC's official count of around 1,700. The massive undercount happens because heat often triggers fatal heart attacks and other conditions that get recorded as the primary cause of death, leaving heat off the death certificate entirely.

• NPR-BU estimates 9,000 annual heat deaths (2018-2025), compared to CDC's official 1,700, with some years exceeding 10,000. The true figure could be even higher due to data limitations.
• Heat is killing people nationwide, not just in hot states. Massachusetts officially reports 5 heat deaths yearly but likely has 60+; Michigan reports 10 but likely has 100+; Florida officially counts 47 but likely has 1,900+.
• Most counties lack protocols to identify heat's role in deaths. Maricopa County (Phoenix) is an exception with trained death investigators, but places like LA and Houston report almost no heat deaths despite modeling suggesting hundreds occur annually.