Ocean acidification is the process by which the ocean's pH decreases over time due to the absorption of carbon dioxide (CO2) from the atmosphere. The ocean absorbs about 30% of the CO2 released into the atmosphere, and as levels increase, so do the levels in the ocean. When CO2 is absorbed by seawater, it causes a series of chemical reactions that increase the concentration of hydrogen ions, making the water more acidic. Ocean acidification negatively affects marine life, including coral reefs and zooplankton.