Heat caused by climate change killed nearly three million people worldwide between 2016 and 2023, according to a new report published in the medical journal The Lancet by the Lancet Countdown project, which involved 146 researchers. In 2023, the hottest year examined, heat caused a record 710,000 global deaths, more than 70% attributed to climate change, exceeding deaths from malaria or HIV.
In Puerto Rico, however, there is no uniform and effective system for recording heat-related deaths, the Centro de Periodismo Investigativo (CPI) revealed. Pablo Méndez Lázaro, an author of the Lancet Countdown report on Small Island Developing States that included Puerto Rico and a professor at the University of Puerto Rico’s Medical Sciences Campus, said thousands have died on the island from causes totally or partially related to extreme heat, mostly older adults and people with chronic illnesses, but death certificates rarely name heat.
The island’s Department of Health’s syndromic surveillance system recorded 442 heat- or sun-related illness cases from January to September 2026, compared with 502 for all of 2025. Pediatrician Gredia Huerta Montañez, cofounder of the Puerto Rico chapter of Physicians for Climate Action, said Puerto Rico’s childhood asthma incidence is among the highest of US jurisdictions, and about one in seven island children has asthma.
The Lancet Countdown found health risks from climate change have grown faster since 2016, coinciding with the Paris Agreement’s entry into force.