Study finds climate change poses greater heat risk to older people

Older adults face dangerous heat stress at much lower temperatures and humidity levels than younger people, according to a US study reported by ERR. The researchers found that older people experience more heat stress with a 1.5-degree temperature rise than younger adults do under four degrees of warming.

Climate scientists have long used the physiology of a young, healthy adult to measure heat tolerance. This has overlooked older people’s biological vulnerability, causing previous climate models to underestimate future risks linked to warming.

Each age group has a different tolerance limit

The world’s population is ageing, increasing the number of people vulnerable to heat in the coming decades. By 2050, more than two billion people aged at least 60 are expected to live worldwide, making up almost one-fifth of the global population. Most will live in low and middle-income developing countries on the frontline of global warming.

The human body regulates its temperature mainly through sweating and increased blood flow to the skin. As people age, the function of the sweat glands weakens, reducing the body’s ability to cool itself efficiently. The heart also becomes less able to pump blood to the skin’s surface. As a result, extreme heat can become life-threatening for older people at much lower temperatures and humidity levels than for younger adults.

To assess the risks more accurately, the study’s authors tested people’s heat tolerance in specialised climate chambers. The team observed young, middle-aged and older people in increasingly hot and humid conditions.

The researchers determined a critical limit for each age group, known as the wet-bulb temperature, beyond which the body can no longer maintain its heat balance. Once that threshold is exceeded, a person’s body temperature begins to rise dangerously.

The team then compared the biological measurements taken in the laboratory with global climate projections. The comparison showed that existing models had underestimated the danger. Adding age-related thresholds to the computer models increased the number of people at risk several times over. The number experiencing intolerable heat stress was as much as eight times higher than previously estimated, with older people forming the largest high-risk group.

As the planet warms, intolerable heat will occur more often and across more regions. For every additional degree of warming, one billion more people will experience extreme heat stress for at least 180 hours a year. Older people will bear the greatest burden.

Heat will also affect agriculture

Heat is not distributed evenly across the planet but primarily affects the tropics and subtropics. Densely populated regions such as the Indus-Ganges Plain and the Persian Gulf coast face particularly severe conditions.

With three degrees of global warming, parts of South Asia will become intolerable for living during the summer months.