Increasing meridional disparity of population exposure to heat stress

• Global uneven heat exposure follows a meridional S-shaped pattern in 21st century. • Low-latitude countries face twice the uneven heat exposure risk of other areas. • SSP3 shows the highest heat exposure risk among all population scenarios. • Rising heat exposure under climate and socioeconomic change poses unequal risks globally. Global warming and socioeconomic development are expected to exacerbate human exposure to heat stress, but the extent and inequality of such changes remain unclear. Here, we quantified the future population exposure to heat stress (PEHS) under different Shared Socioeconomic Pathways (SSPs) and Representative Concentration Pathways (RCPs) scenarios using a novel decomposition framework that separates the contributions of climate change, population change, and their interaction. Results show that global PEHS will increase substantially during the 21st century, with low-latitude regions experiencing the largest absolute increases, and high-latitude regions facing the largest relative increases. Globally, projected increases in PEHS under SSP3–7.0 are roughly three times those under SSP1–2.6, with low latitudes contributing about 70 %–75 % of the global total. SSP1–2.6 most effectively limits future heat exposure, with the highest risks in low-latitude developing regions, underscoring the need for low-emission pathways and targeted population and urbanization management. The findings highlight the urgent need for both climate mitigation and population adaptation strategies to address the growing and uneven heat exposure risks worldwide.