Acidic Oceans

June 15, 2008
By Damond Benningfield

The oceans have been working hard the last few decades to remove extra carbon dioxide from the air -- pollution from burning fossil fuels. Climate experts say that helps slow down the rate of global warming. But the creatures that live in the oceans may soon pay a price for it. The upper levels of the oceans are becoming more acidic, and that could hurt much of the marine ecosystem.

Estimated change in sea-surface pH from the 1700s to 1990s, red being the most change toward more acidic. Credit: Global Ocean Data Analysis Project (GLODAP) - National Oceanic & Atmospheric Administration, U.S. Dept of Energy, National Science Foundation

Marine plants take in carbon dioxide from the atmosphere and convert it to food. Animals eat the plants, and use some of the carbon to make shells and skeletons. When those organisms die they settle to the bottom, where the carbon from the shells and skeletons is eventually incorporated into new layers of rock. And that keeps the carbon out of the air.

But carbon dioxide can also dissolve directly into the water -- something that’s happening at a rapid pace. That creates carbonic acid -- the same stuff that gives soda pop its fizz. This acid makes it harder for corals, shellfish, and microscopic organisms to make their shells. Without shells, the animals can’t survive.

Coral reefs may be at greatest risk. Corals are very sensitive to even small environmental changes. A temperature rise of just one or two degrees can kill an entire reef, for example. A study released in December 2007 says that if the current trends hold up, by 2050 almost all of the world’s coral reef habitats will be too acidic. And since reefs attract many types of fish and other organisms, the whole reef ecosystem could be in danger.