Anthropogenic (man-made) carbon dioxide is responsible for adding to global warming and triggering a host of attendant environmental problems. CO2 has also contributed to a dramatic spike in the acid levels of the oceans - an effect that has been cast as the 'evil twin' of climate change.When carbon dioxide dissolves in the oceans it alters the water chemistry - lowering the pH and increasing acid levels.Roughly a quarter of the carbon dioxide in the atmosphere ends up in the oceans where it forms carbonic acid.Bärbel Hönisch - a paleooceanographer at Columbia U's Lamont-Doherty Earth Observatory - is the lead author of a new study that appeared in Science. Hönisch points out a key difference between acidification events in the past and the current situation impacting the oceans:What we're doing today really stands out... We know that life during past ocean acidification events was not wiped out -- new species evolved to replace those that died off. But if industrial carbon emissions continue at the current pace, we may lose organisms we care about -- coral reefs, oysters, salmon.Increases in CO2 absorption has the effect of depleting carbonate ions which weakens the ability of corals to develop shells - making it more difficult for coral skeletons to form. Other marine organisms with shells that contain calcium carbonate are also increasingly at risk, for example calcareous plankton. The apt term "osteoperosis of the sea" has been coined to describe this effect.Coral reefs aren't just an underwater spectacle to be enjoyed by scuba divers, they are critical from a survival standpoint. Ocean Acidification.net notes that "Nearly 500 million people depend on healthy coral reefs for sustenance, coastal protection, renewable resources, and tourism, with an estimated 30 million of the world's poorest people depending entirely on the reefs for food."Rising ocean acidification has implications for life at all levels of the marine food chain. In the course of a recent study scientists found that water with high acid levels interfered with the ability of clown fish to use smell as a detector. Instead of swimming away from predators - they swam toward them. National Oceanic and Atmospheric Administration chief Jane Lubchenco told AP: "We're just beginning to uncover many of the ways in which the changing chemistry of oceans affects lots of behaviors... salmon not being able to find their natal streams because their sense of smell was impaired, that's a very real possibility." It's a serious threat that we minimize at our peril. The carbon dioxide we have already pumped into the atmosphere will continue to be absorbed by the oceans for decades. Adding to the atmospheric carbon load by exploiting fossil fuels simply compounds an already serious problem.NRDC documentary on the challenge of ocean acidification:

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