Climate change adaptation efforts are challenged by rapid population ageing and thus an increased proportion of vulnerable individuals. Despite its importance for adaptation planning, the link between ageing demographics and climate adaptation, particularly green infrastructure development, remains unexplored. Here we employ high-resolution satellite images and the difference-in-differences framework to assess the spatiotemporal relationship between ageing demographics and green space coverage change patterns across 26,885 Southeast Asian communities over the past two decades. We find that cities with an increased concentration of elderly residents exhibit greater vulnerability due to inadequate green infrastructure provision. The findings reveal green space reduction in ageing communities, which is more pronounced in socio-economically disadvantaged, rapidly ageing cities. Nonetheless, coastal cities, facing higher climate risks, exhibit no such decline due to their functional demand. Our results support considering socio-demographic shifts and geospatial disparities in city adaptation strategies.,Rapid population ageing is challenging for climate adaptation. Considering ageing demographics and green infrastructure development in 26,885 Southeast Asian communities, the authors find a reduction in green space in ageing communities, especially in socio-economically disadvantaged areas, with implications for vulnerability.,