The ability to routinely quantify global carbon dioxide (CO2) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and international coordination have made it possible to measure CO2 absorption by the oceans to a greater degree of accuracy than is possible in terrestrial landscapes. These advances, combined with new satellite‐based Earth observation capabilities, increasing public availability of data, and cloud computing, provide important opportunities for addressing critical knowledge gaps. Furthermore, Earth observation in synergy with in‐situ monitoring can provide the large‐scale ocean monitoring that is necessary to support policies to protect ocean ecosystems at risk, and motivate societal shifts toward meeting C emissions targets; however, sustained effort will be needed. In a nutshell: The oceans cover >70% of the Earth's surface and are critical for food supply and maintaining global climate Increasing carbon dioxide (CO2) absorption alters ocean chemistry and ecology, affecting marine ecosystems over both the short and long term Accurate estimates of CO2 absorption by the world's oceans provide a powerful constraint on carbon (C) budgets, and are needed to inform policies to motivate societal shifts toward reducing C emissions We review recent and foreseeable advances for studying oceanic CO2 absorption, explain why satellite‐based Earth observation is key to addressing existing knowledge gaps, and discuss how global monitoring is now both possible and necessary to support policy and conservation