Linking Climate Trends to Human Health Outcomes

In a warming world, playground slides grow too hot for children, a jog becomes punishing for adults trying to get fit and an evening stroll feels unbearable for older adults.clmate change is exacerbating physical inactivity with dire consequences, driving potentially hundreds of thousands of premature deaths worldwide by 2050, according to a study published Monday in Lancet Global Health.

Climate change is exacerbating physical inactivity with dire consequences, driving potentially hundreds of thousands of premature deaths worldwide by 2050, according to a study published Monday in Lancet Global Health.

The research adds to an emerging body of scientific literature scrutinizing the far-reaching health effects of rising temperatures driven by greenhouse gas emissions. While researchers have been able to document how climate change kills people directly — with workers succumbing to heat exhaustion and people drowning in floodwaters — they are just beginning to quantify some of the less obvious ways it claims lives.

The authors of the new Lancet paper developed a model based on physical activity surveys and temperature records from 156 countries spanning 2000 to 2022. They concluded each additional month where the average temperature exceeded 82 degrees coincided with a 1.4 percentage point increase in physical inactivity globally.

Projected physical inactivity would continue to rise in the decades ahead, depending on a range of potential climate scenarios — including if the average temperature rose by 1.7 or 2 percent mid-century compared by pre-industrial levels. Right now, the world is on track to warm by between 2.7 and 3.1 degrees Celsius by 2100, according to the U.N. Intergovernmental Panel on Climate Change.

The pattern of rising heat and falling activity was concentrated in low- and middle-income countries, while high-income countries were projected to see no statistically discernable change. Some hot spot countries closer to the equator show estimated increases in physical inactivity of more than 4 percentage points by 2050.

By 2050, the team of Latin American scientists who authored the Lancet paper calculated, this drop in activity could result in 470,000 to 520,000 additional deaths and $2.4 billion to $2.59 billion in annual productivity losses.

These projections are not certain, but provide a warning for how shifts in human behavior as the planet warms could cost additional lives.

Christian Garcia-Witulski, the paper’s lead author, said in an email that heat can make routine walks to work, school and shops more strenuous and discourage regular exercise when people don’t have access to gyms and rely on outdoor activities. Some changes are more subtle: A worker skipping a long walk home in hotter months, ditching their bicycle for a car to commute or feeling too exhausted to work out after spending hours exposed to heat.

“The real-world picture is usually not that people suddenly stop moving altogether,” Garcia-Witulski, a research fellow at the Lancet Countdown Latin America and a professor at the Pontifical Catholic University of Argentina, said. “It is that heat gradually erodes the safe, comfortable, and practical opportunities people have to stay active in everyday life.”

Several climate researchers said that while they could not say for certain why people in higher income countries did not significantly change their level of physical activity as temperatures rose, it could be because they have better access to air conditioning, gyms and flexible work arrangements.

“Wealthier populations can adapt their behavior, whereas many others in the world cannot,” said Luke Parsons, a climate scientist at The Nature Conservancy who was not involved in the study and has researched the toll of extreme heat.

The health consequences of sedentary lifestyles — increased risks of heart disease, diabetes and cancer — is well established. Nearly one-third of adults do not meet the World Health Organization’s global recommendation for 150 minutes of moderate physical activity per week, according to a 2024 study.

“The link between physical inactivity and chronic diseases is so strong that any compromise to achieving regular exercise — in this case excessively hot temperatures — will pose broad public health risks,” said Jonathan Patz, chair of health and the environment at the University of Wisconsin-Madison, who was not involved in the study.

Smog peaks on hot humid days, making it harder to breathe. Sweat struggles to evaporate and keep a person cool in humidity, and older adults already have a harder time sweating. The body works harder to regulate its core temperature, directing blood to the skin and beating the heart faster.

“That extra stress on the body means that the same activity that would feel easy on a cool day becomes genuinely difficult and potentially dangerous on a hot one,” Parsons said. “You hit your limit faster.”

People are more likely to seek refuge in air-conditioned rooms to sit still and beat the heat — encouraging more sedentary behavior.

The study also found a striking gender gap in the association between hotter temperatures and physical inactivity. Looking backward, the researchers found additional hot months were associated with a 1.69 percentage point increase in inactivity for women compared with 1.18 for men, and projected that disparity would continue in the decades to come.

Garcia-Witulski said that evidence suggests men and women regulate heat differently, and that women can also face more caregiving responsibilities and have less access to safe places to exercise.

The model has its limitations, including the fact that physical activity was self-reported and could be skewed. An ideal study would record physical activity using technology such as Fitbits or Apple Watches for more accurate data, but that’s infeasible for research spanning scores of countries of different income levels over decades.

“They are doing the best they can with a study of this scale,” said Nicholas Nassikas, a pulmonologist on faculty for the Center for Climate, Health, and the Global Environment at T.H. Chan School of Public Health at Harvard University, who was not involved in the study.

Survey physical activity data offered national averages, leaving researchers unable to disentangle the effects in different parts of the country or for the type of activity, such as work or leisure.

Drew Shindell, a climate scientist and professor of earth sciences at Duke University who was not involved in the research, noted in an email that the fact that the study also used national temperature averages meant that these broad readings might also obscure massive swings in heat in large countries.

“The U.S., for example, might have a year with warmer than usual temperatures in the South and cooler temperatures in the North that would show up as zero change in their method but could have an enormous impact since the South is hotter,” Shindell said in an email.

The researchers only examined rising temperatures and not other climate impacts that keep people sedentary, such as extreme weather.

Still, the study’s authors said their work illustrates the need to treat physical activity as a priority as countries move to become more resilient to climate change. For example, officials could subsidize cooled exercise facilities for at-risk people, create shaded, tree-lined walking corridors and ensure access to climate-controlled public spaces for people to walk and cycle.

“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,” the researchers wrote.

https://www.washingtonpost.com/climate-environment/2026/03/16/climate-change-sedentary-deaths-lancet-study/