A lesser-known consequence of having a lot of carbon dioxide (CO 2 ) in the air is the acidification of water. Oceans naturally absorb the greenhouse gas; in fact, they take in roughly one third of the carbon dioxide released into the atmosphere by human activities. When CO 2 dissolves in water, it forms carbonic acid, the same substance found in carbonated beverages. New research now suggests that seawater might be growing acidic more quickly than climate change models have predicted.

Marine ecologist J. Timothy Wootton of the University of Chicago and his colleagues spent eight years compiling measurements of acidity, salinity, temperature and other data from Tatoosh Island off the northwestern tip of Washington State. They found that the average acidity rose more than 10 times faster than predicted by climate simulations.

Highly acidic water can wreak havoc on marine life. For instance, it can dissolve the calcium carbonate in seashells and coral reefs [see “The Dangers of Ocean Acidification,” by Scott C. Doney; Scientific American, March 2006]. In their study, published in the December 2 Proceedings of the National Academy of Sciences USA, Wootton and his team discovered that the balance of ecosystems shifted: populations of large-shelled animals such as mussels and stalked barnacles dropped, whereas smaller-shelled species and noncalcareous algae (species that lack calcium-based skeletons) became more abundant. “I see it as a harbinger of the trends we might expect to occur in the future,” says oceanographer Scott C. Doney of the Woods Hole Ocean­ographic Institution, who did not participate in this study.

Wootton notes that the changes his team saw were linked with growing levels of atmospheric CO 2 , but he readily acknowledges that the global-warming gas might not be the main culprit in this surge in acidity. Instead the acidification the researchers observed could have resulted from a nearby upwelling of deep ocean water loaded with carbon, so the results might not apply to the oceans as a whole. Still, the acidity readings along the Pacific coast of the U.S. and in the Netherlands do seem to be rising, Wootton says, “and that seems consistent with our pattern.” Marine life, it seems, may not have the luxury of time to act as a buffer against the changing waters.

Note: This article was originally printed with the title, "Acid Bath".