The scaling of urban climate action and its governance is rapidly becoming a central focus in the urban climate governance literature and policy debates. Building on the broader scaling literature and inspired by related initiatives in other fields, this article calls for the development of a systematic “science of scaling” for urban climate governance. Such a science of scaling may help to give a better understanding of how well-performing urban climate action and its governance can be multiplied, accelerated and broadened (ie horizontal and vertical scaling and scaling out, up and down), and it may help to uncover scaling trajectories towards systemic change in cities (ie deep scaling).