Ocean Acidification

Ocean acidification is the long-term decline in seawater pH and carbonate-ion concentration as the ocean absorbs anthropogenic CO2, which forms carbonic acid. Surface pH has fallen about 0.1 unit since pre-industrial times, roughly a 30 percent rise in hydrogen-ion concentration, and is projected to fall a further 0.3 to 0.4 unit by 2100 under high-emission paths. Lower carbonate saturation makes shell and reef building harder for calcifiers.