Ambitious and rapid action is needed to reduce climate change and its impacts—and the first broad-scale assessment of ocean-based solutions shows the focus should be on the oceans. The study looks at the feasibility of 13 ocean-based measures to reduce atmospheric carbon dioxide (CO2), counteract ocean warming and/or reduce impacts like ocean acidification and sea-level rise. It identifies ocean-based renewable energy as the most promising, and several local marine conservation and restoration options as ‘no-regret measures’, that should be scaled-up and implemented immediately, but concludes all other measures are still too uncertain to recommend without further research. Published in Frontiers in Marine Science as part of the article collection ‘Successes at the Interface of Ocean, Climate and Humans’, the study highlights the trade-offs and governance issues associated with all solutions and emphasizes that the greatest benefit will come from combining global and local solutions through policy cooperation.