When the sun goes down, heat vulnerability remains

• Heat vulnerability at night requires climate justice (and policy) perspective. • The urban heat island effect aggravates climate-driven nighttime warming. • Different stressors should be considered when assessing heat vulnerability at night. • There is a need for specific nocturnal adaptation strategies for heat resilience. Continuously rising temperatures due to climate change allow extreme heat-related risks to persist throughout the entire day. While daytime and nighttime heat are well distinguished in climate research, the social inequities and adaptation strategies linked to nighttime heat remain overlooked. This short communication proposes a multidimensional perspective to nighttime heat, combining recent climate data, vulnerability analysis and urban adaptation strategies. Using Barcelona, Spain, as a city of reference, we discuss how localized urban heat islands, limited access to climate shelters, and stressors like traffic noise levels intersect to shape heat risk and climate injustice at night. Building an equitable climate resilience to nighttime heat means not only mapping where heat remains at night but also designing strategies for night hours and broadening how heat vulnerability is assessed. This piece calls on both researchers and practitioners to consider climate science, social equity and urban policy through a nighttime lens, and consequently, to ensure a more comprehensive way to support vulnerable population groups.