Ocean Acidification

Of the fossil-fuel CO2 emitted globally since the beginning of the industrial revolution, only about half has remained in the atmosphere. The other half (~48%) has been taken up by the ocean. As CO2 dissolves in seawater, the pH of the water decreases, making it more acidic. How marine ecosystems, coral reefs, and fisheries will respond to this rapid acidification is unknown. Corals, calcareous phytoplankton, and other marine organisms use calcium carbonate in seawater to construct their shells and skeletons. In a more acidic environment, it becomes difficult to secrete calcium carbonate, leading to slower growth rates and more fragile skeletal structures. By the middle of this century, the estimated reduction in calcification rates may lead to a situation where we are losing more reef area to erosion than can be rebuilt through new calcification, leading to a potential reduction of 50% of the area of coral reefs worldwide. Experiments have shown that most, but not all, calcifying organisms are already showing signs of skeletal degradation. How this will affect ecosystem community structure and the marine food-web is unclear at present. With this as background and context, the UNESCO-IOC and the Scientific Committee on Oceanic Research (SCOR) have launched a project on The Ocean in a High CO2 World, Included is regular scientific review (~every four years) to assess what is known about these impacts and to highlight this issue at the international and intergovernmental level.