The renowned naturalist and science communicator Sir David Attenborough has been chosen as an exceptional guide to introduce us to the Global Ocean: one great ocean system undergoing epochal changes generated by the climate crisis and its effects. But how can we monitor and observe the oceans and their transformation? We will do so through floating buoys and satellites in orbit, in a sea journey exploring an unstable balance between changing chemical and physical processes. What are the ocean scenarios of the future? Acidification, deoxygenation, mean sea-level rise and overfishing are just some of the issues we will address to understand how and where we can still act to mitigate the effects of the climate crisis and continue preserving this invaluable natural heritage over time.