As a consequence of anthropogenic perturbations the global ocean is warming, acidifying, losing oxygen and sea ice, and sea level is rising. While drastic reduction of the emission of greenhouse gases is urgently needed, which includes ocean energy substitution for fossil energy, we show that the ocean offers numerous opportunities to reduce the causes and consequences of climate change, globally and locally. A wide range of ocean-based measures to enhance societal climate adaptation are currently implemented worldwide to deal either with coastal risks or changes in ocean resources. Ocean-related measures should not be considered as a substitute for climate mitigation on land or non ocean-based adaptation measures, which must be strongly pursued for the benefit of the atmosphere, the ocean, and socio-ecological systems worldwide