A much higher number of elderly people than previously expected are at high risk of illness or death from extreme heat as temperatures climb under the effects of climate change, scientists have discovered. A new study by researchers at Stanford University in the United States factored in the way that age affects the body’s tolerance for heat, shining light on a new level of risk from heatwaves on the global population. As the number of people aged 60 years and older is projected to more than double from one billion in 2020 to 2.1 billion in 2050, representing 21 percent of the world’s population, the Stanford study warns that rising temperatures could become far more deadly than expected.
The new study “reinforces that dangerous heat cannot be defined by one universal temperature threshold. It depends partly on who is being exposed”. As we age, our bodies lose the natural ability to cool themselves – we sweat less and our hearts have to work harder as blood vessels do not expand as much.
As temperatures rise, the body eventually reaches a point at which it cannot cool quickly enough to compensate. This point – known as “uncompensable heat stress” – is reached much sooner and at lower temperatures by elderly people than younger adults. People aged 65 and older face more exposure to uncompensable heat at 1.5C of global warming above preindustrial levels than younger adults would at 4C of warming, the researchers found.
Long-term global warming is currently estimated at about 1.4C above preindustrial levels. The annual global average exceeded 1.5C for the first time in 2024, according to the European Union’s Copernicus agency, but long-term, multidecade warming has not yet crossed this threshold. However, the Stanford researchers estimate that the number of people who experience at least 180 hours a year beyond their age group’s tolerable heat limit is already more than double what it was previously thought to be.
This is a key threshold identified by the report. Extreme “ambient” heat is unusually severe heat, or heat at a level that crosses a climatic or health-related threshold. This can lead to severe illness, such as heatstroke or heart attack, or even death.
It is tricky to predict health consequences from global averages as air temperature alone is not a reliable marker of potential physical danger. Furthermore, only a proportion of deaths during heatwaves are directly caused by hyperthermia – overheating – according to the study, which attributed most cases to comorbidities, particularly cardiovascular, renal and respiratory conditions that are exacerbated by elevated body temperature. Warming around the world is happening at a speed not seen in the past 10,000 years, according to NASA data cited in the Stanford study.
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