Ocean Acidification

Ocean acidification is the name given to the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere. About 30–40% of the carbon dioxide released by humans into the atmosphere dissolves into the oceans, rivers and lakes. To maintain chemical equilibrium, some of it reacts with the water to form carbonic acid. Some of these extra carbonic acid molecules react with a water molecule to give a bicarbonate ion and a hydronium ion, thus increasing the ocean's "acidity" (H+ ion concentration). Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14, representing an increase of almost 30% in H+ ion concentration in the world's oceans,

This increasing acidity is thought to have a range of direct undesirable consequences such as depressing metabolic rates in jumbo squid and depressing the immune responses of blue mussels. (These chemical reactions also happen in the atmosphere, and as about 20% of anthropogenic CO₂ emissions are absorbed by the terrestrial biosphere, also in the ground soils between absorbed CO₂ and soil moisture. Thus anthropogenic CO₂ emissions to the atmosphere can increase the acidity of land, sea and air.)

Other chemical reactions are also triggered which result in an actual net decrease in the amount of carbonate ions available. In the oceans, this makes it more difficult for marine calcifying organisms, such as coral and some plankton, to form biogenic calcium carbonate, and existing such structures become vulnerable to dissolution. Thus, ongoing acidification of the oceans also poses a threat to the food chains connected with the oceans.

Ocean acidification, which like global climate change is driven by increased levels of carbon dioxide, has been regarded by climate scientists as the "equally evil twin" of global climate change.