Overview
- The model identifies a threshold effect, estimating a 1.44 percentage-point rise in global physical inactivity for each additional month with average temperatures above 27.8°C.
- Under high-emissions scenarios, inactivity could increase by up to 1.75 percentage points by 2050, contributing to an estimated 0.47–0.70 million extra deaths annually and $2.4–$3.68 billion in productivity losses.
- Projected impacts concentrate in low- and middle-income countries, with regional hotspots including Central America, the Caribbean, eastern sub-Saharan Africa, and equatorial Southeast Asia, while changes in high-income countries are minimal or non-significant.
- Women and older adults face greater risk due to lower heat tolerance, compounding a world in which about one-third of people already fall short of WHO physical activity guidelines.
- The authors urge urban cooling designs, shaded routes, reflective surfaces, water features, affordable climate‑controlled exercise facilities, heat-risk guidance, and workplace protections, while noting limitations such as self-reported activity data, national annual aggregates, and the exclusion of extreme events.