As global temperatures climb, a silent shift toward inactivity could accelerate deaths and economic losses, especially in the world’s most vulnerable regions.
Study: Effects of climate change on physical inactivity: a panel data study across 156 countries from 2000 to 2022. Image credit: ChameleonsEye/Shutterstock.com
Climate change is increasing global heat exposure, but its effects on physical inactivity have received little attention. A recent modeling study in The Lancet projects that physical inactivity could increase by up to 1.75 percentage points, especially in tropical low- and middle-income regions, and that this could mean up to 0.70 million additional deaths annually under high-emissions scenarios by 2050.
Rising global heat reshapes physical activity patterns
Physical inactivity is a major contributor to poor cardiometabolic health. It is considered to underlie 5 % of adult deaths, accounts for USD 54 billion in healthcare costs, and is responsible for lost productivity worth USD 14 billion.
About a third of the world’s population is sedentary and fails to meet the World Health Organization (WHO) guidelines for physical activity. With increasing global temperatures, physical exertion causes more cardiovascular strain and feels more strenuous. In addition, safe physical activity may become more difficult as extreme weather events become more common and air quality worsens.
This is illustrated by the 28 % rise in the moderate or higher risk of heat stress with light physical activity in 2023 compared to 1990-99. Experts predict that at a temperature 2°C above preindustrial temperatures, more than a quarter of the world’s people could experience an additional month of severe heat stress compared to 1950-79. This would limit the time available for physical activity.
Increases in climate change-related deaths due to noncommunicable disease already disproportionately affect low- and middle-income countries (LMICs). The present study sought to provide a longitudinal assessment of how temperature affects physical inactivity over more than 20 years and to predict future health and economic costs if such trends continue under different climate scenarios.
Global analyses project future inactivity and economic burden
The researchers examined thousands of observations linking temperature to physical inactivity across a panel of 156 countries between 2000 and 2022. This allowed them to estimate how heat exposure was associated with changes in physical activity, while adjusting for the effects of socioeconomic and environmental factors.
This was combined with projected changes in temperature to predict shifts in physical inactivity rates by 2050, accounting for socioeconomic parameters across multiple shared socioeconomic pathway scenarios. Finally, these were converted into health and economic costs using country-specific economic and labor-participation metrics.
Rising temperatures linked to deaths and productivity losses
The initial baseline analysis shows that over 25 % of the world’s population is physically inactive, with women more so than men. The mean annual temperature was 19·2°C, with a wide range from sub-zero to > 28 °C.
Similarly, physical activity spanned a wide range, but was broadly linked to climate. Even so, some colder areas had high rates of physical activity, including North America and Argentina.
The model predicted a 1.44 percentage-point increase in physical inactivity globally with each additional month of temperatures >27.8 °C, highlighting a non-linear relationship with effects concentrated above this threshold. This would disproportionately affect women and older adults since previous research has shown that heat-compensation mechanisms, such as sweating, are less efficient in these groups.
When adjusted for income, it became apparent that climate-driven increases in inactivity would chiefly target LMICs. Inactivity was estimated to rise by 1.85 percentage points in LMICs, compared to minimal or non-significant changes in high-income countries. There were several hotspots where the impact was largest. These included: Central America, the Caribbean, Eastern sub-Saharan Africa, and Equatorial Southeast Asia. These trends remained consistent with further subgroup analyses.
The models also showed that at this level of heat exposure, the estimated number of additional deaths by 2050 could range from 0·47 to 0·70 million per year. In addition, productivity losses could reach USD 2·40–3·68 billion in the projected scenario.
This would correspond to approximately 7–11 % of the 2022 deaths caused by inactivity, and up to 7.9 % of the productivity loss. Here again, the economic loss would chiefly impact LMICs. The projected increase in deaths from all causes due to physical inactivity would also be most marked in LMICs, while remaining low across industrialized countries.
The authors note that this would perpetuate and exacerbate existing inequities, as most laborers in LMICs must work during the hot hours. Heat stress is projected to lead to a loss of approximately 5 % of working hours in the hottest parts of the world, according to separate global labour projections.
Meanwhile, climate-controlled spaces are largely out of reach in such regions, especially for underprivileged groups like women. Moreover, the rising rates of cardiometabolic disease cannot be easily factored into public health budgets in these countries.
The authors suggest that urgent mitigating measures should be taken, such as improved urban design to cool cities and encourage physical movement. This could include connected shaded pathways, reflective, heat-permeable surfaces, more water features, and access to affordable, climate-controlled exercise facilities.
Health policy should also embrace population-wide education on heat risk across various types and intensities of physical activity, and promote adaptive strategies for safe activity in hotter climates.
Study limitations
Despite careful data analysis, several limitations should be considered. Physical activity estimates were based on self-reported data, which may introduce recall and social desirability bias. The use of annual, nationwide data limited the ability to account for seasonal variation and age-specific patterns. The study also did not differentiate between types of physical activity, such as voluntary versus mandatory activity, which may obscure behavioural differences.
In addition, the analysis did not account for changes in urbanisation or migration over time, potentially weakening comparisons of exposure. Socioeconomic and health indicators were measured at the country level, which may allow for residual within-country confounding. Finally, extreme weather events were not included in the modelling, which could influence the projected rates of physical inactivity.
Climate-driven inactivity threatens health and economic stability
The findings have profound implications for climate-driven changes in inactivity, which slow economic growth and eventually lead to many additional deaths.
Treating physical activity as a climate-sensitive necessity – rather than a discretionary lifestyle choice – will be essential to prevent a heat-driven sedentary transition and its accompanying surge in cardiometabolic diseases and economic losses.