To keep global temperature rise to within 1.5 degrees Celsius (°C), we need to reach net-zero carbon dioxide (CO2) emissions as soon as possible by utilizing deep and unprecedented emissions reductions across all sectors, as well as large-scale carbon dioxide removal (CDR) to extract carbon dioxide from the atmosphere.

The ocean is already a major carbon sink and plays a crucial role in global climate regulation. Ocean-based carbon dioxide removal approaches are receiving increasing attention in plans to achieve net-zero emissions. However, most approaches are still in the early stages of development, have a high degree of uncertainty about their efficacy, pose environmental and social risks, and lack sufficient governance to ensure responsible deployment.

This report explores seven ocean CDR approaches that are in various stages of development and deployment: coastal blue carbon restoration, seaweed cultivation, ocean fertilization, alkalinity enhancement, electrochemical approaches, artificial upwelling, and artificial downwelling.

This report outlines a pathway forward that is centered on informed and responsible development and deployment of ocean CDR to appropriately balance the urgency of emissions reductions with taking a precautionary approach regarding the environmental and social risks of ocean CDR.

Executive Summary:

Ocean carbon dioxide removal approaches have been gaining prominence in international and national climate policy. Yet many of these approaches remain untested with significant scientific gaps and risks to the marine environment and coastal communities. Striking the right balance between the urgency of emission reductions and using appropriate ocean carbon dioxide removal approaches without causing further harm to ocean systems, ecosystems, and coastal communities will require an iterative and adaptive approach that prioritizes responsible and informed development.