Naturally, the ocean stores CO2 from the atmosphere. In the past 20 years the amount of CO2 in the atmosphere has been increasing. The increase of CO2 in the atmosphere has lead to the ocean to absorb more CO2. When the CO2 reacts with water it creates carbonic acid, which then dissolves in the water to release a hydrogen ion and another acid, simultaneously making the ocean more acidic. The hydrogen ion then reacts with the carbonate ion, one of the things that are needed to make calcium carbonate. The lack of carbonate ions in the water leads to trouble for marine life that create shells, like coral. They can’t make the shells needed to live.