Heat stress risk for older adults could become significant at much lower levels of global warming than conventional assessments suggest, according to new research published in The Lancet Planetary Health. The study indicates that people aged 60 and above may experience uncompensable heat stress (UHS) at around 1.5°C of warming above pre-industrial levels, compared with about 4°C for younger adults. UHS occurs when the body can no longer shed enough heat to maintain a stable internal temperature, increasing the risk of severe illness and death.

The findings matter as the world’s population ages alongside a warming climate. The number of people aged 60 and above is projected to reach 2.1 billion by 2050, roughly double the current population in that age group. This means a growing number of people could face dangerous heat exposure, particularly in already hot regions.

Why Older Adults Are More Vulnerable

The human body relies heavily on sweating and increased blood flow to the skin to release excess heat. These mechanisms become less effective with age.

• Older adults generally sweat less, while their cardiovascular system has to work harder to move blood toward the skin.
• Their blood vessels also have a reduced ability to widen, limiting heat loss.
• Existing physiological research has found that older adults reach uncompensable heat conditions under lower combinations of temperature and humidity than younger adults.

This difference is important because earlier heat-risk assessments often applied thresholds developed for younger adults to the wider population.

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Age Changes the Heat Threshold

The new research separates the population into younger, middle-aged and older groups rather than treating adults as having the same physiological response to heat.

The study estimates that each additional 1°C of global warming could expose roughly one million more people to at least 180 hours of UHS annually. Older adults are expected to carry a disproportionate share of that exposure.

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Heat Risk Is Already Visible

The warning comes as countries are experiencing increasingly severe heat events. In England, the UK Health Security Agency estimated that heatwaves in May and June 2026 together resulted in 2,877 excess deaths, compared with 1,504 during the summer of 2025.

Researchers say the consequences are likely to be particularly serious in low- and middle-income countries, including India and Pakistan, where high temperatures can combine with humidity, limited access to cooling and large vulnerable populations.

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Why the 1.5°C Threshold Matters

The significance of the finding is not that every person aged over 60 will become dangerously overheated once global temperatures reach 1.5°C. Heat stress depends on local temperature, humidity, exposure duration, activity, clothing, shade and access to cooling.

Instead, the research suggests that climate assessments based on a single heat threshold may underestimate how many older people are exposed to physiologically dangerous conditions.

Other experimental research supports the age-related difference. A study of 100 adults found that older participants had lower critical environmental limits than younger adults during light activity, meaning their bodies lost the ability to maintain heat balance under less severe environmental conditions.

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Protecting an Ageing Population

The findings point toward a need for heat-warning systems and public-health planning that account for age rather than relying on one temperature threshold for everyone.

That could mean earlier warnings for older adults, access to cooled spaces, checks on people living alone and better planning for homes and care facilities during prolonged heatwaves.

As global temperatures rise and the older population expands, heat stress risk for older adults is becoming not only a climate issue but also a growing public-health challenge. The study’s central warning is that dangerous heat may arrive for vulnerable populations well before conditions reach the extreme thresholds traditionally used to define human heat limits.

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