Rising Nighttime Temperatures and Sleep Loss

This indicator tracks the relationship between human sleep and warmer night-time temperatures. It employs estimates from a multi-country sleep study that measures over ten billion sleep observations from fitness bands between 2015–2017. The indicator estimates percentage change in annual total number of hours of sleep lost globally due to warmer than optimal nighttime temperature relative to the 1986-2005 baseline average.

This indicator has two main limitations. First, it assumes findings from the underlying global study generalise to people outside the sample. Because participants owned fitness trackers, they were likely wealthier than average, and evidence shows poorer individuals experience greater sleep loss from warm nights, meaning the indicator likely underestimates global sleep loss. Second, the temperature–sleep relationship may shift as populations adapt (for example, through wider air conditioning access), a growing concern for projections further into the future. However, the underlying study already included regions with high air conditioning use, and recent follow-up research confirms the relationship persists.