New Study: Older Adults Far More Vulnerable to Extreme Heat Than Previously Thought

Scientists at Stanford University in the United States have released a new study showing that the number of older adults at high risk of illness or death from extreme heat is far greater than previously estimated. The research examined how aging bodies differ in heat tolerance, clarifying new risk levels from heatwaves for global populations.

The global population aged 60 and above is projected to rise from 1 billion in 2020 to 2.1 billion by 2050, accounting for 21% of the world's population. The Stanford study warns that rising temperatures could lead to more deaths than expected.

Speaking to Al Jazeera, Chris Mullington, honorary clinical lecturer at Imperial College London in the UK, commented: “Previous assessments often assumed everyone can tolerate heat like a healthy young person, which significantly underestimated the risk to older adults. This new study reinforces that dangerous heat cannot be defined by a single universal temperature threshold; it also depends on who is exposed.”

Why Are Older Adults More Vulnerable to Extreme Heat?

As we age, our bodies lose their natural cooling ability: older people sweat less, and the heart has to work harder because blood vessels do not dilate as effectively. When temperatures rise, the body reaches a point where it can no longer cool down fast enough, known as “uncompensable heat stress.” Older adults reach this point earlier and at lower temperatures than younger people.

The study found that at 1.5°C of global warming above pre-industrial levels, people aged 65 and above face more uncompensable heat stress than younger people do at 4°C of warming.

Current long-term global warming is estimated at about 1.4°C above pre-industrial levels. According to the European Union's Copernicus Climate Change Service, the global average temperature exceeded 1.5°C for the first time in 2024, but the long-term warming trend over decades has not yet crossed this threshold.

The Stanford researchers estimate that the number of people experiencing at least 180 hours per year above their age group's heat tolerance is already more than double what was previously thought. Mullington explained: “These 180 hours are accumulated over the year and need not be continuous. What matters is describing exposure to conditions that may be uncompensable; not everyone exposed will become ill.” However, it means older adults face risk of heat-related death and illness at far lower temperatures than previously believed.

How Does Extreme Heat Affect the Human Body?

Extreme heat can lead to serious conditions like heatstroke, heart attacks, and even death. However, predicting health outcomes from average air temperature alone is difficult, because humidity, sunlight, air movement, physical activity, clothing, and individual heat loss capacity all play significant roles.

This means conditions a healthy young person can endure may cause older adults to accumulate heat, raising their core body temperature and leading to serious illnesses like heatstroke. Additionally, according to the study, only a small fraction of heatwave deaths are due to direct hyperthermia; most are caused by underlying conditions such as cardiovascular, kidney, and respiratory diseases exacerbated by elevated body temperature.

Where Are Older Adults Hit Hardest?

According to NASA data cited in the study, global temperatures are warming at a rate unprecedented in the last 10,000 years. Meanwhile, the world's population is aging rapidly due to increased life expectancy and declining birth rates, putting more people at risk from heat.

Older adults in low-income countries like China, India, and Pakistan face the highest risk, even with only 1.5°C of global warming. As temperatures rise further, affected regions expand. According to the study, each additional 1°C above pre-industrial levels puts about 1 billion more people into the category of experiencing 180 hours of uncompensable heat stress annually, most of them elderly.

At 3°C of warming, the authors project that India, China, Pakistan, and Bangladesh would have 1.5 billion people facing this condition, nearly three-quarters of the global total affected.

What Solutions Can Mitigate Extreme Heat Impacts?

The study concludes that understanding where, when, and to what extent human heat tolerance is exceeded is crucial for developing risk reduction strategies. Proposed adaptation measures include: redesigning urban landscapes to expand green spaces, improving ventilation, reducing heat emissions from human activities, establishing cooling centers, and enhancing heat warning and response systems.

These efforts can prioritize vulnerable communities, especially older adults who may be socially isolated, economically disadvantaged, or have chronic conditions. Since most heat-related deaths among older adults occur indoors, ensuring access to air conditioning or other cooling facilities with reliable energy infrastructure is also a critical recommendation. In the long term, reducing greenhouse gas emissions remains key to controlling global warming.