As cities around the world experience rapid sea level rise (SLR), institutions and actors classify and measure SLR “risks” through discourse and specifying practices for adaptation. These risk, discourses, and practices occur at multiple scales that are embedded within one another and draw their significance from cross-scalar connections; from global estimates of ocean density and emission scenarios, local design criteria for flood management, networks of tidal gauges, and individual and collective experiences of loss and change. Thus social actors responding to the complex physical challenges posed by climate change across space and time must deal with an inherent politics of building shared understanding and agreeing on (or not) desirable courses of action. These dynamics produce ‘scalar politics,’ i.e. strategies for defining and managing perceived risks at specific scales, resulting in more or less equitable and effective responses to the uneven consequences of SLR. To highlight the scalar politics of knowledge systems in adaptation planning, we present findings from two case studies of the Pacific Islands and coastal areas of Florida, USA. Drawing on our findings, we propose the concept ‘scalar knowledge politics of risk.’ As knowledge claims flow between global, regional, and local decision-making spaces, we identify five scales at which knowledge systems experience friction: 1) construction of the global climate; 2) regional downscaling of climate impacts; 3) local definition of risks; 4) transformation of on-the-ground social-ecological-technical systems and infrastructures; and, 5) evaluation of interventions. Through our case study investigation of the scalar politics of SLR adaptation, we hope to help illuminate and inform strategies to overcome long-standing barriers to effective and inclusive urban adaptation
