The last time the oceans endured such a drastic change in chemistry was 65 million years ago, at about the same time the dinosaurs went extinct. Though researchers do not yet know exactly what caused this ancient acidification, it was directly related to the cataclysm that wiped out the giant beasts. The pattern of extinction in the ocean is consistent with ocean acidification--the fossil record reveals a precipitous drop in the number of species with calcium carbonate shells that live in the upper ocean--especially corals and plankton. During the same period, species with shells made from resistant silicate minerals were more likely to survive.
The world's oceans came close to an acidic catastrophe one other time about 55 million years ago, when the temperature of the Earth spiked and large amounts of methane and/or carbon dioxide flooded the atmosphere. There is no evidence, however, that this caused a mass extinction event.
"Ultimately, if we are not careful, our energy system could make the oceans corrosive to coral reefs and many other marine organisms," Caldeira cautions. "These results should help motivate the search for new energy sources, such as wind and solar, that can fuel economic growth without releasing dangerous carbon dioxide into the environment."