The just-released Intergovernmental Panel on Climate Change (IPCC) special report on the ocean and cryosphere in a changing climate (SROCC) (1) details the immense pressure that climate change is exerting on ocean ecosystems and portrays a disastrous future for most life in the ocean and for the billions of people who depend on it unless anthropogenic greenhouse gas (GHG) emissions are slashed. It reinforces in stark terms the urgency of reducing carbon emissions expressed in a 2018 IPCC report (2). But another just-released report (3) provides hope and a path forward, concluding that the ocean is not simply a victim of climate change, but a powerful source of solutions. Drawing on this report organized by the High Level Panel (HLP) for a Sustainable Ocean Economy, which quantifies and evaluates the potential for ocean-based actions to reduce emissions, we outline a “no-regrets to-do list” of ocean-based climate actions that could be set in motion today. We highlight the report’s analysis of the mitigation potential and the required research, technology, and policy developments for five ocean-based mitigation areas of action: renewable energy; shipping and transport; protection and restoration of coastal and marine ecosystems; fisheries, aquaculture, and shifting diets; and carbon storage in the seabed (see the figure). Make no mistake: These actions are ambitious, but we argue that they are necessary, could pay major dividends toward closing the emissions gap in coming decades, and achieve other co-benefits along the way (3, 4).