Ocean acidification is the reduction in the pH of the ocean over an extended period, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere. Since the beginning of the industrial revolution (200+ years ago), the concentration of carbon dioxide in the atmosphere has increased due to human activities, such as burning fossil fuels and deforestation, and surface ocean waters has become 30 percent more acidic (i.e., pH has fallen). Because the ocean absorbs about 30% of the carbon dioxide in the atmosphere, increasing levels of anthropogenic carbon dioxide in the atmosphere results in increased carbon dioxide in the ocean. When carbon dioxide is absorbed by seawater, chemical reactions occur that reduce seawater’s pH and its carbonate ion concentration. 

Many marine organisms (e.g., oysters and other bivalves, sea urchins, corals, and calcareous plankton) use carbonate to build shells and skeletal structures. Therefore, decreases in seawater carbonate ions can make it difficult for these organisms to build and maintain shells and skeletal structures, resulting in biological and physiological impacts that can affect organisms’ survival and growth, as well as ecosystems. 

The global impacts of ocean acidification on marine life lead to economic impacts on commercial fisheries and tourism to cultural impacts on indigenous people. For example, the U.S. Pacific Northwest is seeing the direct effects of ocean acidification, especially on its shellfish industry.