Extreme heat could leave millions more adults inactive by 2050

A new study suggests that extreme heat could cause millions more adults to become insufficiently active by 2050, contributing to almost 700,000 additional premature deaths every year.

The results frame exercise as a climate issue influenced by shade, working hours and access to cooled indoor spaces.

Extreme heat drives inactivity

In 156 countries, exceptionally hot months appeared not only in meteorological data but also in the number of adults failing to meet healthy activity thresholds.

Christian García-Witulski, Ph.D., of the Pontifical Catholic University of Argentina (UCA), compared hotter and cooler years and found that increasing heat led more people towards inactivity.

Every additional month above 28°C increased inactivity by 1.44 percentage points globally and by 1.85 points in lower-income countries.

These figures show that heat is more than an everyday inconvenience: it can alter the ways people work, travel and exercise.

Physical activity protects health

Consistent movement supports heart health, blood-sugar regulation, mood and sleep by enabling muscles to use energy and blood vessels to function more effectively.

According to the World Health Organization (WHO), 31% of adults and 80% of adolescents do not achieve recommended activity levels.

For clear health benefits, adults typically require at least 150 minutes of moderate activity a week, or 75 minutes of vigorous activity.

When people do not move enough, the risk increases because inactive muscles use less glucose and fat, gradually placing extra pressure on the heart and metabolism.

Diverging paths in a hotter climate

By 2050, inactivity is projected to increase by 0.98 percentage points under lower-emissions conditions and by 1.75 points under the hottest pathway.

Climate pathways are standard scenarios used by climate scientists to turn decisions on energy, population and development into estimates of future heat.

The largest predicted increases would occur in hot equatorial areas, including Central America, the Caribbean, eastern sub-Saharan Africa and equatorial South-East Asia.

Belgium and Finland would experience minimal change, highlighting the role of latitude and cooling capacity in determining risk.

Inequality shapes heat exposure

Heat affected countries unevenly, with poorer areas recording greater rises in inactivity because cooling and secure indoor spaces require money.

A lack of shade, unreliable air conditioning and inflexible work schedules can turn hot months into missed opportunities to walk, cycle, play or train.

“This is not just a climate story, it is also an inequality story,” said García-Witulski. This unequal exposure means health guidance on its own cannot resolve a problem embedded in streets, homes and timetables.

Age and gender differences

The effect of heat was stronger among women than men, while nations with older populations also saw larger increases.

Biological factors may contribute, as cooling relies on blood flow and sweating, both of which vary by age and sex.

Social expectations can create an additional barrier where women have less time, safety or access to cool locations for exercise.

These trends suggest that standardised heat advice is less useful than support directed at those facing the most restricted options.

How the figures were calculated

The researchers relied on annual country-level records, meaning each nation supplied one temperature pattern and one activity estimate for each year.

To reflect actual exposure to heat, they used population-weighted temperature, which gives less importance to uninhabited areas.

They assessed unusually hot years against each country’s own longer-term pattern, helping to distinguish the effect of heat from culture, geography and income.

Although this approach reinforces the connection with heat, it cannot establish every individual reason for remaining indoors.

The added cost of lost work

Reduced physical activity also has an economic impact, as illness and premature death cut the time people are able to work.

One assessment estimated that physical inactivity caused $13.7 billion in productivity losses across 142 countries in 2013.

By 2050, inactivity driven by heat is projected to add $2.40 billion to $3.68 billion in annual costs to the global economy, depending on the extent of warming.

Separately, the International Labour Organization (ILO), a United Nations labour agency, warns that heat can reduce workers’ pace or prevent work altogether.

Limits on the findings

Several important limitations mean the figures should not be treated as an exact prediction for every neighbourhood.

Activity data came from self-reported surveys, in which respondents describe their own behaviour, meaning recall and social pressure may affect the answers.

Yearly national averages also conceal seasonal shifts, city-level differences in heat, and whether activity is undertaken for work, transport or leisure.

The analysis did not include other climate hazards, such as floods, heavy rainfall and hurricanes, so it may miss some disruption.

Cooling preserves choices

Cities can reduce the danger by viewing shade, water and cooled rooms as public-health measures rather than optional extras.

Heat-adaptive urban design, which aims to keep roads and parks cooler, can allow people to walk or cycle without excessive strain.

Low-cost indoor exercise facilities become important when outdoor routes are unsafe during the hottest parts of the day.

“In practical terms, climate-resilient physical activity policies are those that help people remain active safely even under hotter conditions,” said García-Witulski.

Making movement possible

In a warming world, daily movement increasingly depends on public decisions, including shaded streets, workplace protections and affordable cooled spaces.

Cleaner energy and better design could help more people remain active, although forecasts are still constrained by national-level data and climate shocks that have not been measured.