News release

From: The Lancet

Older people face dangers from heat exposure at much lower temperatures than previously thought, global study suggests

Older people face serious health risks from heat at lower temperatures than previously estimated, suggests new research published in The Lancet Planetary Health journal. Previous studies relied heavily on measurements from healthy young adults to estimate when temperatures and associated humidity would become challenging for the human body. Because older people are generally less able to regulate their body temperature (they tend to sweat less, their blood vessels respond more slowly, and their hearts work harder in the heat), these studies may have underestimated the number of people at risk from extreme heat by at least twice what earlier studies estimated.

This new study accounts for age-related differences in heat tolerance on a global scale. Researchers drew on previously published laboratory experiments that measured heat tolerance separately for three age groups: younger adults (15–39), middle-aged adults (40–59), and older adults (60 and over). Next, they mapped where heat would become dangerous for each group, and how many people would be affected. To do this, the researchers used a high-resolution heat stress metric across different scenarios ranging from 1 to 4°C of global warming above pre-industrial levels (in 0.5°C steps), combined with population projections.The study estimates that at 1.5°C of warming, 22% of the world's older adults (290 million people) would face unsafe heat for at least a month each year (based on at least 180 hours of dangerous heat a year, assuming roughly six hours of such heat per day). Their estimates suggest that young adults wouldn't face a similar level of risk until 4°C of warming, when 17% (490 million people) would be affected. Each additional degree of warming exposes roughly one billion more people to at least 180 hours of temperature-humidity combinations beyond which their heat balance cannot be physiologically maintained.South Asia and the Persian Gulf regions are shown to be most exposed. There, older adults could face dangerous heat day and night for three months straight once warming reaches 3°C or above. At that level, just four countries—India, China, Pakistan, and Bangladesh—would account for 1.5 billion people, or 73% of the total population affected worldwide, across all age groups. The authors warn that the greatest challenge falls on countries that combine high heat exposure with high poverty rates and limited access to cooling, including India, Pakistan, Bangladesh, Myanmar, and Niger.The authors call on governments to develop heat emergency plans and improve access to cooling and heat warning systems. They also say that cutting emissions remains essential to reduce older people's risk of prolonged, round-the-clock heat danger and protect future generations from widespread heat exposure.