Step 2: Explore the concept of ocean acidification. When excess CO$_2$ is absorbed by seawater, it reacts with water to form carbonic acid (H$_2$CO$_3$). This process lowers the pH of the ocean, making it more acidic. Acidification can harm marine organisms, especially those with calcium carbonate (CaCO$_3$) shells or skeletons, such as corals, mollusks, and certain plankton species.