Greenhouse gases are turning the oceans acidic decades earlier than predicted with potentially catastrophic consequences for marine life, scientists have warned.
The acid in sea water is powerful enough to dissolve the shells of sea creatures, they said. An American team has found evidence that an acidic "tipping point" has been reached on the continental shelf along the west coast of North America.
The work underlines rising concerns that man-made emissions will affect the world's oceans, through acidification, in a much more direct way than climate change.
"This is potentially very bad news," said Paul Halloran, of Oxford University, an expert in the field. "The impact on tourism and fisheries may have huge economic consequences."
A team led by Dr Richard Feely, of the US government's National Oceanic and Atmospheric Administration in Seattle, reports that waters which a century ago were not corrosive have now become acidic enough to dissolve shells.
Marine scientists have known for years that water below a certain depth corrodes shells as a result of acid produced by ''rotting" organic matter that floats from the surface to deep waters. But scientists are alarmed to see that the level at which water becomes corrosive is now high enough to be washed up on to the continental shelf - where many vulnerable organisms live.
Increased acidity may also directly affect the growth and reproduction rates of fish.