Atmospheric carbon dioxide has risen from 280 to 409 ppm since the industrial revolution. This increase in carbon dioxide has led to a 0.1 decrease in pH, and it could decrease by 0.5 by 2100. When carbon dioxide meets seawater, it forms carbonic acid; the molecules dissociate into hydrogen, bicarbonate, and carbonate, and they lower the pH of the ocean. Sea surface temperature, ocean acidity, and dissolved inorganic carbon are also positively correlated with atmospheric carbon dioxide. Ocean acidification can cause hypercapnia and increase stress in marine organisms, thereby leading to decreased biodiversity. Coral reefs themselves can also be negatively affected by ocean acidification, as calcification rates decrease and acidity increases.
Aragonite is impacted by the process of ocean acidification because it is a form of calcium carbonate. It is essential in coral viability and health because it is found in coral skeletons and is more readily soluble than calcite. Increasing carbon dioxide levels can reduce coral growth rates from 9 to 56% due to the lack of available carbonate ions needed for the calcification process.Other calcifying organisms, such as bivalves and gastropods, experience negative effects due to ocean acidification as well. The excess hydrogen ions in the acidic water dissolve their shells, limiting their shelter and reproduction rates.
As a biodiversity hotspot, the many taxa of the Great Barrier Reef are threatened by ocean acidification. Rare and endemic species are in greater danger due to ocean acidification, because they rely upon the Great Barrier Reef more extensively.  Additionally, the risk of coral reefs collapsing due to acidification poses a threat to biodiversity. The stress of ocean acidification could also negatively affect other biological processes, such as reducing photosynthesis or reproduction and allowing organisms to become vulnerable to disease.