Emergency departments are seeing a measurable surge in visits during extreme heat, according to a new study published on August 31, 2026 in Nature Health. Researchers say the findings suggest health systems no longer need to wait months to understand who is being harmed during heat waves, and could instead use near-real-time data to respond while the danger is still unfolding.
The study, led by teams at the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health and Boston University School of Public Health, analyzed 8.1 million emergency department visits from the summers of 2023 to 2025. Using de-identified electronic health records from Truveta member health systems across 19 Eastern U.S. states, the researchers linked daily maximum temperatures with emergency visits for all causes, heat-related illnesses, kidney diseases and psychiatric conditions.
Real-time data could sharpen public health responses
According to the researchers, the approach offers a proof of concept for turning health records into actionable intelligence during an ongoing climate event. They said that if hospitals and public health officials can identify, for example, older adults with kidney disease driving a spike in emergency visits, they could increase outreach, protect dialysis access and adjust staffing before the next surge arrives.
The study also found only a modest decline in heat-related emergency visits between the June and August 2025 heat waves, suggesting that adaptation measures may not be reducing risk as much as expected. The researchers said those two events alone were responsible for more than 13,000 excess emergency department visits, underscoring the pressure that extreme heat can place on health services.
A growing challenge for vulnerable patients
The findings are especially relevant for patients with conditions that can worsen in hot weather, including kidney disease and psychiatric illness, as well as older adults who may be more vulnerable to dehydration and heat stress. The authors said timely population health surveillance could help clinicians and planners identify risk earlier and test whether local interventions are working before the season ends.
The research was published as part of a broader effort to improve preparedness for climate-related health threats. The authors argued that faster access to real-world data could help health systems respond more effectively to extreme heat, which is becoming longer, more frequent and more dangerous.
In the UK, the implications may extend to emergency departments, community services and public health teams preparing for hotter summers. While the study focused on U.S. data, the authors said the model could help other health systems monitor risk and intervene sooner as extreme heat intensifies.
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