This chapter extends the discussions of habit to the process of adapting to anthropogenically induced global warming. We reveal the role of designed practices, products, and infrastructures in habituating urban populations to a changing climate. Our central concern is the ‘world within the world’ that design has helped to create. In the rapidly densifying city, atmospheric commons are shaped and reshaped by human design; climate change is lived and felt in hostile heat islands and polluted and particulate-laden city air. Design offers a critical perspective on the dynamics that have shaped the city and organized the civic practices of its inhabitants. We apply ‘defuturing’ as a critical deconstructive mode of reading, derived from the work of Fry (1999), to point to the designing relations shaping city atmospheres, infrastructures, and modes of habituation. Design’s ontological capacity is a second-order agency which is rarely considered in the contexts in which design is most powerfully deployed to shape the materiality of the city. We argue, as a practice involved in deliberately shaping future sociomaterial contexts, that design is a crucial factor in climate adaptation and the forms that such adaptation takes. This chapter reclaims ‘coolth’ as a critical term to describe the experience and sensation of feeling (temperature) cool, recognizing that climate-aware modes of dwelling must be both cultivated and habituated by design.