Changing climate alters the time people spend outdoors

• Annual outdoor time in China is projected to decrease by 52–53 h by 2050. • Elderly, female, and rural populations will be mostly affected by climate shifts. • Daily temperature range and urbanicity dominate the outdoor time reduction. The time people spend outdoors is crucial for public health from both physical and mental aspects, as well as the energy consumption for indoor activities. The impact of climate change on the outdoor time remains unexplored. Here, we employed a two-stage analytical approach to estimate the baseline and future outdoor activity duration among the Chinese population. Using a Bayesian linear multilevel model, we analyzed the relationship between environmental and population-related variables and the time spent outdoors, based on Chinese Environmental Exposure-Related Human Activity Patterns Survey of 160,926 participants from 31 Chinese provinces. We then projected changes in time spent outdoors in 2050 under two climate scenarios: SSP126 (sustainable development) and SSP585 (fossil fuel-driven). Our analysis revealed that the annual cumulative count of time spent outdoors (CTO) is expected to decrease by 52 (95 % Bayesian credible interval: 3–101) hours (SSP126) to 53 (3–104) hours (SSP585) by 2050 across mainland China, with the most significant reductions occurring in summer. Among all population subgroups, elders, females, and rural population are most affected by changing climate. The daily temperature range and urbanicity act as main drivers contribute to the changes in CTO. The decrease in CTO will lead to increased indoor activity, which may cause higher energy consumption and greater health risk. Our findings highlight the need for adaptive measures to mitigate the adverse effects of climate change and emphasize the importance of promoting the sustainable development.