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Oceans to acid

Oceans act as giant sponges for CO2 - but what eases global warming harms marine life.

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Call it the case of the missing "greenhouse gas." For years, scientists have been trying to figure out where carbon dioxide goes once humans generate it. Significant amounts billow into the atmosphere. But each year, atmospheric CO2 concentrations have been rising only half as fast as humans supply the gas.

The hiding place, it turns out, is the world's oceans. And the implications for marine life are troubling, researchers say. If industrial CO2 emissions continue to increase at their current rate, by the end of the century the surface waters of the world's oceans are likely to become more acidic. Though the change appears subtle, it could threaten key organisms at the base of the marine food chain and further endanger shallow-water reefs, which represent some of the most biologically productive ecosystems on the planet. The absorption of this extra carbon dioxide would induce changes in ocean chemistry not seen for at least 20 million years, some researchers say.

"A lot has been said about carbon dioxide in the atmosphere" and its impact on climate, says John Raven, a marine biologist at the University of Dundee in Scotland. But geophysical chemistry also "has pretty firmly established that when CO2 in the atmosphere dissolves into the ocean, the surface ocean will become more acidic. That is something that is happening."

The oceans have been viewed as a potential brake on global warming through natural and engineered approaches to storing carbon- dioxide there. Ironically, it now seems that increased ocean uptake of CO2 "is not a good thing overall," he says.

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