‘A sobering preview’: extreme heat now affects one in three people globally, study finds | Extreme heat

Climate disruption is reducing the time people can safely go about their lives, according to a study that shows a third of the world’s population now resides in areas where heat significantly limits activity.

Rising temperatures, caused by the continued burning of fossil fuels, make it difficult for even many young and healthy adults to perform basic physical activities, such as household chores or climbing stairs during the day, at the height of summer, the report warns.

The limits are greater for older people, who have less ability to sweat and therefore control their body temperature, according to the research, which combines physiological studies on heat tolerance with seven decades of global and regional data on population, temperatures and human development.

On average, the report found that people over 65 now experience around 900 hours of heat each year that significantly limit the safety of outdoor activities, compared to 600 hours in 1950. That’s the equivalent of more than a month’s day.

The most affected are those in the poorest countries or regions, even if they are much less responsible for climate change than rich consumers whose lifestyle produces higher greenhouse gas emissions due to the combustion of gas, oil and coal. In some tropical and subtropical regions, heat restricts the outdoor activities of older people for between a quarter and a third of the year. The most serious challenges are found in Southwest Asia (Bahrain, Qatar, Kuwait, United Arab Emirates, Iraq, Oman), South Asia (Pakistan, Bangladesh, India) and parts of West Africa (Mauritania, Mali, Burkina Faso, Senegal, Djibouti and Niger).

Within countries, there are huge variations by geography, income group and types of work. In India, limitations are most pronounced in the Indo-Gangetic plain and eastern lowlands, and less evident in the Western Ghats and Himalayan foothills. Meanwhile, in South America, people in the Amazon basin are far more vulnerable than those in the Andean highlands. In many Gulf states, the wealthy can mitigate risks with air conditioning, while poorer migrant workers are exposed to dangerous levels of solar radiation on construction sites and when doing other work outdoors.

The study, led by Nature Conservancy scientists and published Tuesday in the journal Environmental Research: Health, goes further than previous research on global heat risks by examining the social and physiological capacity to adapt to heat.

The authors measure “liveability” at different temperatures in MET, a unit equivalent to the average energy expenditure of a human at rest. A manageable temperature is one in which people under the age of 65 can perform up to 3.3 METs of activity – such as sweeping a floor or walking at a moderate pace – for an extended period of time without heat stress, meaning they can regulate their core body temperature to a stable state. In contrast, “unlivable limitations” are found in hot places during hours when human activity is limited to 1.5 METs, which are mainly sedentary activities, such as lying down or sitting.

To examine the vulnerability of different age groups, researchers used measurements of sweat production and “skin wetting” of individuals exposed for varying durations in thermal chambers.

They compared trends over time by comparing quality of life limitations between early periods (1950-1979) and later periods (1995-2024) in their datasets. This revealed that more and more people in a growing region of the world are suffering quality of life limitations due to rising heat. By far the most severe restrictions came in the final year of the study, 2024.

The authors said the findings showed the need for rapid action to reduce the planet’s main sources of heating: oil, gas and coal. They also called on policymakers to direct resources to the most affected communities, age groups and regions.

“Hundreds of millions of people can no longer go about their daily lives safely outside during the hottest times of the year,” said Luke Parsons, lead author of the study. “And these people are overwhelmingly in countries that have contributed the least to the problem. Every fraction of a degree of additional warming will increase these impacts. 2024 has given us a sobering glimpse of what 1.5°C of warming is. [above preindustrial levels] what the world might look like, and it should strengthen our collective resolve to avoid the 2Cs or higher.

“In the short term, investments in heat early warning systems, cooling infrastructure, and protection of the elderly and outdoor workers in the most affected regions are urgent. However, these local investments do not replace the fundamental need to limit global warming.”