Known as the 'other carbon problem', ocean acidification is a critical consequence of rising carbon dioxide levels in the atmosphere. The ocean absorbs nearly 30% of carbon dioxide (CO₂) emissions from human activities, driving this process. As our oceans become increasingly acidic, marine ecosystems and the organisms that inhabit them face significant challenges.

1. Carbon dioxide (CO₂) from the atmosphere dissolves in the ocean, creating aqueous carbon dioxide (CO₂ (aq)).
2. This dissolved CO₂ reacts with water (H₂O) to form carbonic acid (H₂CO₃).
3. Carbonic acid then breaks down into bicarbonate (HCO₃^-) and hydrogen ions (H⁺). The increase in hydrogen ions makes the ocean more acidic. As more carbon dioxide is absorbed, the ocean becomes increasingly acidic due to the rising number of hydrogen ions.
4. Natural processes like the weathering of rocks help counteract this increase in acidity. For example, chalk (CaCO₃) from eroding cliffs is added to the ocean over time. Carbonate ions (CO₃^2-) from the chalk react with the hydrogen ions, forming more bicarbonate ions (HCO₃^-). This process, called buffering, reduces the number of carbonate and hydrogen ions in the ocean.
5. However, this buffering comes at a cost. Marine organisms that build shells or skeletons from carbonate have fewer carbonate ions available. This change places stress on these species, forcing them to use extra energy to build their structures, leaving less energy for growth and reproduction. In severe cases, the ocean's acidity may reach a level where shells or skeletons start to dissolve to buffer the ocean's pH, endangering these organisms even further.