Global Warming Effects Around the World

Ocean Chemistry

The world's oceans are becoming more acidic, threatening sea life.

Elkhorn coral
See how increased ocean acidification from global warming threatens the Carribean's coral reefs—and find other hot spots threatened by higher air temperature on the Climate Hot Map.

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The acidification of the oceans due to climate change impairs the ability of coral reefs and shelled organisms to form skeletons and shells.

Acidification occurs when the oceans absorb CO2 from the atmosphere. Here is how this works. The ocean has dissolved inorganic carbon in three forms—most as bicarbonate, a little bit as carbonate and a very tiny part as carbon dioxide, or CO2. As more CO2 from the atmosphere dissolves into the ocean, it changes the relative proportion of these three, making the water more acidic. Specifically, it reduces the concentration of carbonate ions in surface ocean water by 10 percent, compared with pre-industrial levels. This is significant because coral reefs and shelled marine organisms need carbonate ions to form the lime or calcium carbonate that composes their skeletons and shells.

Some research shows that if atmospheric concentrations of CO2 reach 520 parts per million—we are at 382 ppm now, and 520 ppm is plausible by mid-century—most of the coral species living in warm ocean waters could scarcely support further growth such as species that have larvae that respond negatively to higher ocean acidity.

See references.

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