Extreme temperatures, physical activity, and adaptation

Humans undertake physical activity daily, yet we know little about how climate change might affect this fundamental aspect of life. Using 24 billion person-minute observations from a sample of Fitbit users in the United States, this paper estimates behavioral and performance responses to extreme temperatures. I find significant reductions in activity on hot and cold days, though intraday and interday substitution mitigates this effect. Regions with hotter climates are less sensitive to extreme heat, evincing adaptation. Physical activity projections incorporating this heterogeneity and allowing places to adapt to their future climate imply large welfare gains, unlike projections that ignore adaptation. • Extreme hot and cold temperatures lead to significant reductions in physical activity. • People shift activity within and across days toward more moderate temperatures. • Heterogeneous responses across climate regions suggest adaptation.