Acidic oceans
After absorbing a large proportion of the carbon dioxide released by human activities, the oceans are becoming acidic. If it weren’t for the oceans, the level of carbon dioxide in the atmosphere would be much higher.
The effect could be that fish, squid, and other gilled marine animals may find it harder to "breathe", as the dissolved oxygen essential for their life becomes difficult to extract as water becomes more acidic. And shellfish, crabs, lobsters, and corals may find it more difficult to build their calcium carbonate shells. In some areas, calcium carbonate shells may even start to dissolve.