Sea Sick: The Global Ocean in Crisis by Alanna Mitchell

An important, accessible and deeply concerning book. From the problems with pH, plankton and corals, to overfishing and melting ice, Sea Sick explores the state of the world's oceans and how they are being negatively impacted by climate change.

While it is hard not to despair, Mitchell makes the best case she can for hope and action.
If curious in the topic, recommended. If not, try to read something on it anyway as the issue is of great importance. For example, plankton, not trees, are the larger 'lungs' of our planet, producing half of all the oxygen we breathe.