Disentangling urban vulnerability to rising temperatures

Rising temperatures are already taking a severe toll on human health, contributing to an estimated average of 546 000 heat-related annual deaths globally.1,2 The temporary exceedance of 1·5°C above pre-industrial levels in 2024 shows that the world is rapidly approaching the planetary boundary for climate change, with escalating risks to lives, livelihoods, and health systems.3 The distribution of these heat-related risks is geographically uneven, with cities emerging as hot spots: more than half of the global population lives in urban areas, which have higher temperatures than do their rural surroundings due to dense built environments, extensive impervious surfaces, and related human activities (ie, the urban heat island effect).