The process by which carbon dioxide gas (or CO2) is absorbed by the ocean from the atmosphere and reacts with seawater to produce acid, resulting in a reduction in the pH of the ocean over an extended period of time. (Source: National Oceanic Atmospheric Administration, U.S.A.)

Increased carbon dioxide (CO2) is altering the chemistry of the surface oceans and causing them to become more acidic. The process could have significant consequences on marine organisms which may alter species composition, disrupt marine food webs and ecosystems (Source: UNEP)