Climate change is not only increasing the frequency of heat waves-it is actually reducing the amount of time people can move, work or engage in physical activity outdoors. A new international study published in the scientific journal Environmental Research: Health shows that hours of extreme heat that can limit physical activity have doubled in recent decades since the mid-20th century.
The research combined more than seventy years of climate, demographic and physiological data to assess not only how warm the planet is getting, but what this means for the human body. The result is that about one-third of the world’s population now lives in areas where heat significantly limits daily activities, especially during the middle hours of summer days.
The effects are particularly pronounced among the elderly. People over the age of 65 now experience about 900 hours per year of hot conditions that make outdoor activities difficult or risky, compared with about 600 recorded in the 1950s.
When heat becomes a physical limitation
The human body is able to maintain internal temperature within safe limits by sweating and blood circulation. But when temperature and humidity exceed certain thresholds, these mechanisms become less effective.
Scientists evaluated this threshold using so-called METs (metabolic-quivalent of task), an indicator of the energy required to perform various activities. Under favorable weather conditions, a person can perform moderate activities – such as walking briskly or doing household chores – without problems. In extreme heat, however, the safe activity level drops to almost sedentary behaviors, such as sitting or lying down.
This means that climate change is not only affecting ecosystems or economies-it is beginning to redefine the physiological limits of daily life.
A growing public health problem
Reducing physical activity is a little-discussed but potentially very relevant effect. Regular movement is a major preventive factor for cardiovascular disease, diabetes, and obesity.
If the heat reduces the hours available for walking, working or playing sports, the impact is reflected on the entire health system. Scholars now speak of a dual effect of climate change on health: on the one hand the direct risks of heat waves, and on the other the indirect consequences related to a more sedentary lifestyle imposed by temperatures.
The most vulnerable groups are the elderly, outdoor workers and people living in densely built-up urban neighborhoods, where the so-called “heat island” phenomenon can raise temperatures several degrees higher than in rural areas.
Cities in the heat trap
Urban areas are among the places where this phenomenon occurs most intensely. Asphalt, concrete and traffic accumulate heat during the day and slowly release it at night, making nighttime temperatures increasingly high.
In many European cities, tropical nights-those in which the thermometer does not fall below 20 degrees-have become increasingly frequent. This reduces the body’s physiological recovery and makes it more difficult to perform physical activities even in the morning hours.
This is why urban planners and climatologists are increasingly insisting on the need to adapt cities to the new climate: more trees, permeable surfaces, shade and water have become key tools for reducing heat buildup.
Adapting to a Warmer Planet
Meanwhile, people’s habits are already changing. In many regions of the world, sports activities, physical work and even daily routines are shifting to the early morning hours or evenings, when temperatures are lower.
It is an adaptation that tells well of the magnitude of the ongoing change. Global warming is not only altering Earth’s climate: it is changing the very rhythm of human life, shrinking the hours when we can move around safely and making heat a new variable in everyday life.
