Population heat exposure has increased substantially, resulting in serious effects on human health. However, all previous assessments on global-scale heat exposure focused on the daily scale, limiting accurate estimation of heat duration and the related extent of spatial disparity of population heat exposure. Here, based on high-spatial-resolution hourly temperature and age-group population datasets, we unveil the global hourly population exposure to extreme heat in the last decades. The results show that extreme heat (≥46 °C) hours per heat day have increased by 0.4 h between 1979 and 2023. As the number of heat hours and population have increased, surface air temperature-based extreme heat exposure increased by about 60% (from 3.7 × 1011 person-hours to 5.9 × 1011 person-hours), and universal thermal climate index (UTCI)-based extreme heat exposure increased by about 70% (from 1.5 × 1012 person-hours to 2.6 × 1012 person-hours) between 2000 and 2020. There is a large disparity between the hourly and daily extreme heat exposures, stemming from the change in the number of heat hours per heat day. The most pronounced discrepancy is in UTCI-based very strong heat exposure, with an average disparity equivalent to 2.6 × 1010 person-days. Moreover, global hourly population heat exposure exhibits a distinct inverted-pyramidal structure with increase in age. This is attributed to young people exposed to heat stress outnumbering the elderly, and disproportionately more young people residing in hotter regions. For heat exposure of all age groups, the population effect and interaction effect are dominant factors for the increased heat exposure in tropical regions, while the warming effect primarily drives that in temperate zones. Our study highlights the need for and urgency of health risk assessment based on hourly heat exposure.

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