The first thing to understand is that the industrial revolution has contributed carbon dioxide (CO2) to the atmosphere. This CO2 joins CO2 that was there naturally. For as long as humans have been on the planet, there has been an approximately-constant amount of CO2 in the atmosphere. That amount has gone through fairly regular cycles of climbing to a higher level, then falling back to a starting point, then climbing again.
Higher levels of CO2 blankets the earth and that causes solar warming of the planet. Lower levels allow more heat to escape and we have cooler temperatures. Thus, we have had ice ages and warm spells associated with the pattern seen above for hundreds of thousands of years.
Since the industrial revolution, human use of fossil fuels has added excess CO2 into the air. This is more than the self-regulation of the earth has managed during those hundreds of thousands of years. In all the previous time, the CO2 level in the atmosphere has not been more than about 285 parts per million. Now, the level has gone way higher, passing 350 parts per million and now passing 400 parts per million and still climbing rapidly.
The result has been a rise in temperature and rising sea level as glaciers melt.
The rate at which CO2 increased wasn't as fast as expected, however. For a while that was puzzling. Then it was discovered that CO2 was being absorbed by the oceans at a faster rate than expected, leaving less in the atmosphere.
CO2 in water is what produces the fizz in soda pop. It is a weak acid, but strong enough that you can put an egg in a jar of soda pop and the acid in the soda will dissolve the hard shell from the egg, leaving it soft. The egg's shell is made of calcium, and when it mixes with the CO2 in the water, the result is Calcium Carbonate, which dissolves.
So, while the ocean “saved the planet” from experiencing as much solar warming as might have happened, there was another effect, and that is a problem that we only partially understand. Calcium is important to all plants and animals. In animals it produces our skeletons. Some animals, like humans, have skeletons inside their bodies. Other animals like clams and shrimp have their skeletons on the outside of their bodies.
Currently, the acidity (measured with “ph”) in the Pacific ocean varies with currents. Much of the time it is now so acidic that oyster “seed” (baby oysters) cannot create their shells, and will die. Some of the time the acidity lowers far enough that you can set seed out into the ocean and they do survive. As time goes on, more CO2 will be dissolved from the atmosphere, and the portion of time that allows oyster seed to survive will decrease.