As global temperatures rise, people are becoming less physically active, and this shift could lead to hundreds of thousands of additional premature deaths worldwide in the coming decades, a new study finds. 

Researchers from a group of Latin American universities analyzed World Health Organization (WHO) global health surveys and temperature data from the Climatic Research Unit dataset at the University of East Anglia that included 156 countries between 2000 and 2022.

They found that for each additional month with average temperatures above 82 degrees Fahrenheit, physical inactivity increased by 1.4 percentage points worldwide, according to the study published in the journal The Lancet Global Health.

Rising temperatures could lead to 470,000 to 700,000 additional deaths worldwide each year by 2050, driven by hotter weather that may make people less physically active.

Currently, only about 65% of people worldwide get enough exercise, but inactivity already contributes to roughly 5% of global deaths, according to the WHO. 

In the computer simulations used in the study, rising heat worsened the problem. Tropical low- and middle-income countries in regions such as the Caribbean and sub-Saharan Africa would likely be hit hardest, the study found.

For example, in Somalia, deaths could reach as high as 70 per 100,000 people by 2050 because extreme heat will make it very difficult to move outdoors comfortably and safely.

Many of the most affected tropical areas are also the least equipped to manage the health effects of rising temperatures, the study noted. These regions already have higher levels of physical inactivity and often lack resources, such as air-conditioned spaces, that help people stay active during extreme heat.

Hot weather discourages physical activity because movement becomes both psychologically and physically more challenging, leading people to move less, the study found. 

Women and older adults may feel the effects more strongly because their bodies often have a harder time cooling down, Christian García-Witulski, lead study author and research fellow at the Lancet Countdown Latin America and a professor at the Pontifical Catholic University of Argentina, told ABC News.

“What this tells us is that heat is not only a comfort issue, but that it is changing behavioral patterns at scale,” he said.  

“And because physical inactivity is a key risk factor for non-communicable diseases, this implies relevant impacts for health and the economy,” García-Witulski said, adding that a growing body of evidence has linked heat exposure to an increased risk of cardiovascular strain and dehydration.

Even high-income countries such as the United States will not be immune to rising temperatures. The study predicts the U.S. could see about 2.5 deaths per 100,000 people from heat-related physical inactivity by 2050, an increase from  relatively low levels currently.

“Greater adaptive capacity, such as air conditioning, climate-controlled gyms and indoor physical activity infrastructure, buffers the effect,” García-Witulski said. “However, this can also create a false sense of security, because air conditioning, while it protects from heat, tends to promote sedentary behavior.” 

The researchers say policymakers should redesign cities to help people stay active in hot conditions. They also recommend clearer public health messaging about how to exercise safely in high temperatures and expanding access to climate-controlled places where people can remain physically active.

However, those changes do not address the underlying driver of the problem: rising global temperatures.

“Our results show that the difference between a low-emissions scenario and a high-emissions scenario is enormous,” García-Witulski said. “We go from 470,000 to 700,000 additional deaths worldwide, and from 2,400 to 3,680 million international dollars in losses. This underscores that ambitious emissions mitigation is essential to avoid a heat-induced transition toward sedentary behavior.”