Acidification of the oceans means "double trouble" for marine life from corals to shellfish since it is adding to stresses caused by global warming, a study showed on Wednesday.
"The oceans are more acidic than they have ever been for at least 20 million years," according to the report by the European Science Foundation. On current trends, seas could be 150 percent more acidic by 2100 than they were in pre-industrial times.
Sea water is acidifying because carbon dioxide, released to the atmosphere from burning fossil fuels, is slightly corrosive in water. That makes it harder for creatures such as corals, lobsters, crabs or oysters to build their protective shells.
"Ocean acidification...is double trouble because it is happening on top of global warming," Jelle Bijma, lead author of the report and a professor at the Alred Wegener Institute for Polar and Marine Research in Germany, told Reuters.
"Coastal zones such as in the Mediterranean and North Seas are rich in calcifying organisms such as shellfish that may be particularly sensitive to large changes in carbon chemistry," a statement said.
Seas have already become 30 percent more acidic in the past 200 years -- the oceans have absorbed about 430 billion tons of carbon dioxide, or about one third of emissions by human activities since the Industrial Revolution.
Some fish stocks were moving polewards because their normal habitats were getting warmer. But that meant they were reaching new areas with a different mix of species.
"They have to compete with ecosystems that have been there for ages and that's trouble," Bijma said. The report, by experts in Europe and the United States, is to be presented to governments on May 20, which is European Union Maritime Day.
Among worrying precedents were fossil records of a leap in ocean acidity 55 million years ago that caused a spasm of extinctions of creatures living on the ocean floor, he said. That pulse may have been caused by natural releases of methane.
Bijma said that creatures such as corals or sea butterflies, a type of sea snail, could now be among the most vulnerable to acidification since they relied on easily dissolved aragonite to build their skeletons.
Some types of marine life, especially some plants, were likely to grow better in warmer, more acidic seas.
The report urged European governments to do more to understand acidification through research. It also urged cuts in emissions of greenhouse gases. A U.N. summit in December fell short of agreeing a new treaty to slow warming.
"Existing research has mainly been initiated by individual researchers or teams, with limited overall coordination," the statement said.
'Double trouble' in acidic, warming oceans: study
Acidification of the oceans means "double trouble" for marine life from corals to shellfish since it is adding to stresses caused by global warming, a study showed.