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Why ocean acidification is a climate indicator

About a quarter of the carbon dioxide emitted into the atmosphere is currently taken up by the oceans, where it reacts with seawater and forms carbonic acid. This “acidification” of global oceans is observed as lower pH levels. Since preindustrial times, the average pH of ocean surface water fell from 8.21 to 8.10. While that does not sound like much, that is a 30 percent increase in acidity, and it could decrease another 0.3 pH units by the end of the century. At that rate, it would create an ocean more acidic than any seen in the past 100 million years.

The current rate in acidity change is about 50 times faster than any known historical change, making it difficult for marine life to adapt. Carbonate ions in the ocean become less abundant in a more acidic ocean, making it difficult for shellfish (clams, oysters, mussels) to build shells and skeletons. Additionally plankton, which form the base of the oceanic food web, also have trouble adapting. In a cascading effect, this will alter ecosystems in a way that could threaten seafood staples around the world. More than 1 billion people rely on oceans for food, as well as their livelihood. By one estimate, ocean acidification will cost the global economy $1 trillion annually by 2100. Corals are similarly threatened. With less calcium carbonate available, it hinders the ability for corals to maintain their reefs, which are important habitats for other marine organisms and provide some coastal protection from storms.

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