Introduction:
Both daytime and nighttime temperatures are rising with the latter exceeding the former in magnitude across most global settings. An accumulating body of globally extensive, longitudinally deep, and plausibly causal evidence confirms that unseasonably warm ambient temperatures harm human sleep and reduce time slept. This within-person relationship generally persists in sign but decreases in magnitude when temperature is measured outdoors vs. indoors, during winter vs. summer, and when measured in rich vs. poor socioeconomic contexts.
Purpose: While both national and global population sleep data remain elusive, there is a need to provide an evidence-based accounting of the annual human sleep loss attributable to nighttime warming to inform global policy.
Method: We couple globally gridded ERA5 reanalysis meteorological and climate data over land from 1986-2023 with temperature attributable sleep loss damage functions from a recent wearables-based global temperature and sleep individual panel analysis spanning 68 countries (n=47,628) to hindcast the additional annual cumulative sleep loss attributable to recent nocturnal warming in 2023 and prior five years (2019-2023) compared to the 1986-2005 climate normal baseline.
Results: We estimate that nighttime warming attributable sleep loss has increased by an average of 5% over the last five years (reaching a record 6% in 2023) compared to the average annual sleep loss during the 1986-2005 baseline. Absolute impact estimates vary widely globally.
Conclusions: Nighttime warming attributable sleep loss is likely already a pervasive phenomenon, even among those with socioeconomic adaptive advantages. We conclude by outlining emerging evidence that suggests these absolute estimates may indeed be highly conservative.