SummaryBackground Climate change is amplifying heat exposure worldwide; however, its consequences for global physical inactivity, and the resulting effects on mortality and economic burden, remain unquantified. Methods We analysed a longitudinal dataset spanning 156 countries from 2000 to 2022 using a binned fixed-effects panel regression model. The model examined the relationship between the primary outcome—the age-standardised prevalence of physical inactivity in adults (aged ≥18 years) —and annual exposure to different temperature ranges. Estimated exposure coefficients and climate projections under different shared socioeconomic pathways (SSPs) were used to forecast future physical inactivity. Using relative-risk estimates for all-cause mortality, we converted projected physical inactivity into excess deaths and valued lost productivity using a friction-cost approach calibrated to each country's gross domestic product and labour participation rates. Findings Each additional month with a mean temperature >27·8°C increased physical inactivity by 1·44 (95% CI 0·49–2·39) percentage points globally and 1·85 (0·62–3·08) percentage points in low-income and middle-income countries. By 2050, the prevalence of physical inactivity is projected to rise by 0·98 (0·47–1·49) percentage points under SSP1–2. 6, 1·22 (0·58–1·85) percentage points under SSP2–4. 5, and 1·75 (0·84–2·66) percentage points under SSP5–8. 5, with hotspots exceeding 4 percentage points in Central America, the Caribbean, eastern sub-Saharan Africa, and equatorial southeast Asia. By 2050, these increases translate into an additional 0·47–0·70 million deaths and Intl2·40–3·68 billion in annual productivity losses. Interpretation Rising temperatures are projected to increase the prevalence of physical inactivity, translating into additional premature deaths and productivity losses, especially in tropical regions. Prioritising heat-adaptive urban design, subsidised climate-controlled exercise facilities, and targeted heat-risk communication is essential to mitigate these emerging health and economic burdens, in addition to ambitious emissions reductions. Funding Wellcome Trust 304972/Z/23/Z (Lancet Countdown Latin America).
García-Witulski et al. (Tue,) studied this question.