This dissertation analyzes the emerging epistemologies of climate change in California as articulated by social movements, experts, and subnational governments. As the world's eighth-largest economy and the only state in the U.S. to implement a comprehensive program of regulatory and market-based mechanisms to achieve reductions in greenhouse gas (GHG) emissions, California represents an important site of inquiry. The passage of Assembly Bill 32, the Global Warming Solutions Act of 2006 has made the state a global leader on climate change science and policy innovation. While no subnational government can halt climate change alone, California's environmental policies have a long history of success and replication. Through an extensive analysis of the state's climate policies and interviews with key stakeholders, this dissertation highlights the challenges California faces in influencing global climate policy while addressing the needs of local communities that are already adversely impacted by air pollution. As cities and public agencies appropriate leadership roles in climate governance, policy formulation is increasingly emerging as an expert-driven process that emphasizes global GHG reductions as the goal and geographically-neutral economic and technological fixes as the solution. In this process, community-based strategies that integrate climate change interventions with population health outcomes are often excluded. This dissertation asks how environmental justice advocates are engaging strategically in the policymaking process in order to legitimize or contest regulatory policies regarding climate change in the face of ongoing pollution, illness, and injustice. In answering this question, the dissertation centers on three areas of inquiry: (1) the public health and environmental justice aspects of municipal climate action plans; (2) the conflict over statewide carbon pricing and use of its revenue for investment in communities most impacted by air pollution; and, (3) the social implications of international forest carbon-offset projects allowable under California's market-based climate change law. These cases provide critical insights into environmental inequities and the emerging epistemologies of climate change on multiple scales. The dissertation findings demonstrate that the implementation of climate policies can either serve to exacerbate or redress underlying environmental health inequities in urban communities. In particular, these cases highlight the environmental justice strategies that are challenging a priori policy expertise to produce new local, place-based conceptualizations of climate change that underscore population health and community well-being.