Summary/Abstract
This paper provides a comprehensive and systematic assessment of 13 global- and local-scale, ocean-based climate change mitigation and adaptation measures, including ocean fertilization, alkalization, and hybrid land/ocean methods such as marine BECCS and biochar. It shows that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, dis-benefits, and costs of poorly tested as well as new and emerging measures.