As the Northern Hemisphere grapples with a record-breaking summer of deadly extreme heat, a new modeling study from United States researchers has delivered a stark warning: the public health risk that rising global temperatures pose to elderly communities has been drastically underestimated for decades.
Published in the journal *Lancet Planetary Health* and led by a team from Stanford University, the research addresses a critical gap in earlier climate and heat-related health studies. For years, researchers have relied on wet-bulb temperature — a metric that combines air temperature and humidity to measure how much heat the human body can tolerate before experiencing fatal heat stress. But the foundational data for this metric was collected exclusively from trials on young, healthy adults, failing to account for the biological vulnerabilities that come with age.
Older adults over the age of 60 naturally sweat less than younger people, often live with pre-existing chronic health conditions, and frequently have weakened cardiovascular systems that make it far harder to regulate body temperature during heatwaves. To correct for this gap, the Stanford-led team used updated data from recent wet-bulb experiments that specifically tested heat and humidity tolerance among adults over 60. The researchers then integrated global population aging trends to model heat exposure risks for three separate age groups by the end of the 21st century, under multiple different global warming scenarios.
The study’s core conclusion upends previous projections: “Intolerable heat will be experienced at much larger scales and for longer durations, affecting far more people than previously estimated.”
Breaking down the projected risks, the team found that if the world limits average global warming to 1.5°C above pre-industrial levels — the more ambitious target set by the Paris Climate Agreement — 22 percent of all people over 60 globally will be exposed to unsafe levels of heat for at least one month every year. For every additional 1°C of warming above this threshold, roughly an extra one billion older people will face at least one additional month of heat and humidity that exceeds their body’s ability to cope.
In a worst-case scenario where global average temperatures rise by 3°C by 2100, elderly populations in the hardest-hit regions — including South Asia and the Arabian Gulf — could face round-the-clock dangerous heat for three consecutive months each year. The nations at greatest overall risk are those with high poverty rates and limited access to affordable cooling technology: India, Pakistan, Bangladesh, Myanmar, and Niger top the list of most vulnerable countries.
Beyond the immediate public health death toll, the study warns that widespread unmanageable heat could trigger a new wave of global displacement. “These results suggest that uncompensable heat could increasingly drive internal displacement and transboundary climate migration, raising new policy and humanitarian challenges,” the authors noted.
To avoid these grim outcomes, the research team issued two key calls to action. First, nations must accelerate deep cuts to greenhouse gas emissions to slow the pace of global warming. Second, local and national heat action plans must explicitly prioritize vulnerable older populations, particularly since the majority of heat-related deaths occur indoors. Expanding access to affordable air conditioning and other cooling solutions for low-income and elderly households is a critical public health intervention, the team emphasized.
The findings come as the world already sees the deadly impacts of extreme heat: this summer, a record-breaking heatwave across the Northern Hemisphere has already contributed to tens of thousands of deaths, with Europe — the world’s fastest-warming continent — facing devastating concurrent wildfires, drought, and sustained high temperatures that are on track to make this the hottest summer the continent has ever recorded. Climate scientists project that 2025 will be even hotter than 2024, as rising greenhouse gas concentrations continue to push global average temperatures higher.