arbon dioxide removal (CDR) technologies, also known as negative emissions technologies, appear critical to achieving California's ambitious climate change mitigation goals (Cameron et al. 2017). Negative carbon dioxide (CO 2) emissions cannot be achieved by reducing greenhouse gas (GHG) emissions alone; rather, both emissions reductions and pathways to atmospheric CO 2 extraction are needed to achieve this desired outcome. Yet CDR technologies lack both technical and commercial maturity, and are not yet deployed at industrial scales. In response, numerous state government and nongovernmental organizations in California have taken early steps to support research, development and demonstration (RD&D) of carbon removal (California Air Resources Board et al. 2018; Forest Climate Action Team 2018). There are two general approaches to CDR, biological and engineered (fig. 1). Biological approaches enhance or manipulate natural sinks for CO 2 to store more carbon, typically on land. Engineered approaches apply chemical and physical processes to capture and reliably convert or store CO 2 (Sanchez, Amador, et al. 2018). OUTLOOK UC experts can lead on carbon dioxide removal Through technology demonstration and policy engagement, UC ANR specialists, advisors and AES faculty can support California's ambitions to remove CO 2 from the atmosphere.