Climate change is setting off erratic weather patterns and environmental changes that threaten the livelihood, stability, and survival of the planet. Communities and institutions around the globe are sounding the clarion call about these devastating impacts, advocating for sustainable practices and deep changes to every facet of our lives. This dissertation research consists of an ethnography of a local network of actors and organizations who are responding to climate change, centered on those who define sustainability as integrally connected to justice. I analyze this network of activity through the lens of the concept of an emerging public. I start from the premise that publics are sites that facilitate the potential for collective agency. Publics have the potential to make a wedge between the imperatives that drive the market and the state -- imperatives that are driven by power interests that are largely driving the unsustainable practices that have engendered climate change in the first place. At many points, the research revealed a tenacious gap between an inspired vision of sustainability and justice, and real-life points of entry through which to enact that vision. Participants often felt frustrated that they weren't doing more; that action steps seemed far from the discussions at hand. The data revealed a kind of public incapacity that needed explaining. To this end, I identify three areas that were fundamental to creating openings for agency in emerging publics: discourse, knowledge production, and the structure of publics. I argue that the agentic potential of emerging climate change publics to produce social changes that benefit all citizens is constrained by three tensions observed in this data: 1. the tension between the discursive threads of justice on the one hand, and sustainability on the other 2. the tension between expert and experiential knowledge, and 3. the tension between a desire for inclusive publics, and the reality of their stratification. In conclusion, I argue that if we can see these tensions more clearly, we can work to make publics more effective as sites for unleashing the collective imagination, as well as for generating change that is socially just.