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Oceans in trouble as acid levels rise

June 30, 2005 By Michael Hopkin This article courtesy of Nature News.

Report calls for more stringent carbon cuts to protect seas.

Corals and plankton are at risk of being destroyed by the rising acidity of the world's oceans as the waters absorb carbon dioxide from the air, British scientists have warned. The only solution, they say, is drastic cuts in carbon dioxide emissions, far beyond those called for by the Kyoto treaty.

Without such measures, dissolved carbon dioxide could increase the acidity of sea water by as much as 0.5 pH units by the end of this century, from 8.2 to around 7.7, they say. Such a change would upset the oceans' chemical balance and kill off some marine life.

There is no way for us to remove this CO2 from the ocean. It will take many thousands of years for natural processes to remove it.
John Raven
University of Dundee, UK
"There is no way for us to remove this CO2 from the ocean. It will take many thousands of years for natural processes to remove it," said lead author John Raven of the University of Dundee, at the report's launch in London. As long as we keep putting carbon dioxide into the atmosphere, he added, it will keep finding its way into the ocean. As carbon dioxide dissolves in water it forms weak carbonic acid, which can dissolve materials such as shells and coral.

Since the beginning of the Industrial Revolution, humans have pumped an estimated total of 450 billion tonnes of carbon dioxide into the atmosphere, around half of which has ended up in the oceans, Raven said. He and his colleagues are calling for no more than 900 billion tonnes to be added during this century - a tall order given the burgeoning industrial development of China and India.

This target would call for huge cuts, with emissions by 2100 reaching half their present levels. This is far in excess of the more modest targets set by the Kyoto treaty, which calls for developed nations to cut their emissions, relative to 1990 levels, by an average of 5% by 2012.

Hot water

Without action to combat acidification, the effects are likely to be strongest in the Southern Ocean around Antarctica, the report says1. Tiny shell-forming molluscs called pteropods live here and help form the basis of Antarctic food chains, says Carol Turley of the Plymouth Marine Laboratory. "This is another very strong argument for reducing carbon dioxide emissions," she adds.

Other potential victims would be coccolithophores, tiny hard-shelled plankton that can blossom in huge numbers, forming swarms visible from space.

And while corals face bleaching and death from higher-temperature waters, the report's authors note that acidic waters are a big problem too. They calculate that even under the lowest future scenarios for carbon emissions produced by the Intergovernmental Panel on Climate Change, corals such as those on Australia's Great Barrier Reef could be all but wiped out by 2050 by acidity.

There are a few theoretical quick fixes for ocean acidification, such as dumping limestone into the water to boost mineral levels and buffer the ability of carbon dioxide to change the pH. But we would have to dig up 60 square kilometres of chalk to a depth of 100 metres every year to provide enough, notes study author Andrew Watson of the University of East Anglia in Norwich. This is unfeasible and risks causing further damage to the planet, he adds.

The only answer is to stop burning so much fossil fuel, Watson says. "We are addicted to fossil-fuel burning like a smoker is addicted to nicotine," he says. "Like smoking, there are many adverse effects - we need to wake up and heed the doctor's orders."


  1. Royal Society Working Group on Ocean Acidification. Ocean Acidification Due to Increasing Atmospheric Carbon Dioxide. (2005).


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