Billions of people exposed to increasing heat but decreasing greenness from 2000 to 2022.

Rising heat stress due to climate warming poses a significant threat to human health, and greenness offers a nature-based solution to mitigate heat-related health impacts and enhance resilience. Although global greenness has increased, it remains unclear whether these trends align with the population's heat mitigation needs. In this study, we integrated spatially resolved demographic data with satellite-derived greenness metric and reanalysis-based heat stress data to construct a global profile of joint exposure at 1 × 1 km resolution from 2000 to 2022. We found that 69.3% of global populated areas and 41.3% of the global population (∼2.9 billion people) were exposed to increasing heat stress but decreasing greenness (IHDG), representing the most concerning situation for heat mitigation. Urban populations were disproportionately affected, with 50.8% exposed compared to 27.1% in rural areas. Low- and middle-income countries exhibited more pronounced trends of increasing heat stress and bore the greatest burden from IHDG, accounting for 85% of total exposed populations. Moreover, there was a notable demographic shift in IHDG-exposed populations toward older groups, exacerbating the heat mitigation crisis. This study advances the understanding of the joint dynamics of heat stress and greenness and provides a profile of population exposure at a fine grid level. By highlighting the scale of IHDG conditions, our findings emphasize the urgent need to address this environmental challenge and a significant opportunity for improving greenness to mitigate increasing heat globally. The spatially detailed assessment maps offer essential data for informed decision-making.