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Carbon Dioxide Increase in the Ocean

Carbon dioxide, which accounts for roughly 84 percent of the anthropogenic greenhouse gas emissions into the atmosphere in the U.S., causes 20 percent of the greenhouse effect. However, because carbon dioxide -- unlike water vapor, which is another greenhouse gas ̵1; does not condense, it is responsible for 80 percent of the radiative forcing that raises temperatures. This warming effect would be even greater if the oceans didn't absorb a significant amount of the carbon dioxide produced through human activity. The surplus carbon dioxide acidifies the oceans and poses a threat to some aquatic species.

Ocean Acidification
- Carbon dioxide dissolves in seawater -- a natural process that accounts for about a third of all atmospheric carbon dioxide. The water reacts with carbon dioxide to form carbonic acid. This reaction forms side reactions with calcium carbonate, which is abundant in seawater. The calcium carbonate is left over from the shells of myriad marine species. This side reaction forms more carbonic acid. These reactions acidify the ocean, and because of the increased presence of carbon dioxide in the atmosphere, the pH of the oceans -- a measure of acidity -- has fallen by 0.1 point since the Industrial Revolution. This doesn't sound like much, but it represents a 30 percent increase in acidity.
The Problem of Acidification
- Increased levels of carbon dioxide change the chemistry of the oceans. Ocean pH has remained stable for the last 20 million years, so a 30 percent increase in acidity is a significant change, and threatens the balance of life for aquatic species as well as terrestrial ones. In particular, the reduction in the availability of carbonates makes it harder for creatures to form shells -- as pH levels increase, the shells literally dissolve. The harm to these creatures spreads to those who feed on them, and from there it goes all the way up the food chain to affect human beings.
Future Projections
- The unavailability of carbonate in the oceans could doom such shell-forming species as coral as soon as 2050, according to the Natural Resources Defense Council. Moreover, pteropods, small creatures that are food for salmon and whales, may be unable to form shells in the acidified environment that scientists predict for 2100. Ocean acidification is not the only consequence of increased levels of carbon dioxide in the oceans. It's possible that, because of these increased levels, the oceans will be able to absorb less atmospheric carbon dioxide, and global temperatures will increase even faster.
Uncertainty in the Seas
- Warmer water at the surface of the oceans can hold less carbon dioxide that the colder waters at the sea floor. Thus, when colder water rises to the surface as part of normal ocean-circulation patterns, it brings with it an excess of carbon dioxide, some of which evaporates into the atmosphere. On the other hand, detritus of plants and organisms rains down to the sea floor, where other organisms metabolize the carbon and enrich the sea floor with more carbon dioxide. It isn't clear what effect increased levels of carbon dioxide will have on this "biological pump."

Nature