This paper explores how city planners engaged with global climate scientists to devise contextually relevant strategies to address the urban heat island effect-a potentially dangerous heat event expected to increase along with global warming. Drawing original data from the New York City Regional Heat Island Initiative, a collaborative effort between scientists and urban planners, the paper highlights how global climate science is 'localised' as researchers and policy-makers struggle to make technically legitimate and politically accountable decisions. The paper argues that the localisation of global science often involves a process of co-production, where technical issues are not divorced from their social setting and a diverse set of stakeholders engage in analytical reviews and the crafting of policy solutions. The paper argues that the co-production framework can contribute to more scientifically legitimate and publicly accountable decision-making related to urban climate change.