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Oceans becoming more acidic

The world's oceans are slowly getting more acidic, say scientists.

The researchers from California say the change is taking place in response to higher levels of carbon dioxide in the atmosphere.

The lowering of the waters' pH value is not great at the moment but could pose a serious threat to current marine life if it continues, they warn.

Ken Caldeira and Michael Wickett, from the Lawrence Livermore National Laboratory, report their concerns in the journal Nature.

Increasing use of fossil fuels means more carbon dioxide is going into the air, and most of it will eventually be absorbed by seawater. Once in the water, it reacts to form carbonic acid.

Scientists believe that the oceans have already become slightly more acidic over the last century.

But these researchers have tried to predict what will happen in the future by combining what we know about the history of the