In this Policy Bridge, we present the key issues regarding the safety, efficacy, funding, and governance of coastal and marine systems in support of climate change mitigation. Novel insights into the likely potential of these systems for use in mitigating excess carbon dioxide emissions are presented. There may be potential for coastal blue carbon and marine carbon dioxide removal (mCDR) actions to impact climate change mitigation significantly over the rest of the 21st century, particularly post 2050. However, governance frameworks are needed urgently to ensure that the potential contribution from coastal and ocean systems to climate change mitigation can be evaluated properly and implemented safely. Ongoing research and monitoring efforts are essential to ensure that unforeseen side effects are identified and corrective action is taken. The co-creation of governance frameworks between academia, the private sector, and policymakers will be fundamental to the safe implementation of mCDR in the future. Furthermore, a radical acceleration in the pace of development of mCDR governance is needed immediately if it is to contribute significantly to the removal of excess carbon dioxide emissions by the latter half of this century. To what extent large-scale climate interventions should be pursued is a decision for policymakers and wider society, but adaptive legal, economic, policy, research, and monitoring frameworks are needed urgently to facilitate informed decision-making around any implementation of mCDR in the coming decades. Coastal and ocean systems cannot be relied upon to deliver significant carbon dioxide removal until further knowledge of specific management options is acquired and evaluated.