Researchers have found a new and potentially devastating danger from the huge volumes of carbon dioxide (CO2) produced by industry and transport, already threatening the planet with climate change.
Now, they warn, it is also rapidly turning the world's oceans acid as it is dissolved in seawater, and putting an enormous array of marine life at risk. Ocean acidification may wipe out much of the microscopic plankton at the base of the marine food web, and have a knock-on fatal effect up through shellfish to major human food species such as cod. It is already having a serious impact on organisms such as coral, and putting a question mark against the future of coral reefs.
The findings about acid seas, which are recent, are causing alarm in the international scientific community because they represent a huge threat to the world until now unknown.
They were set out in detail at the conference on climate change at the Met Office headquarters in Exeter, in a paper by scientists from Britain's Plymouth Marine Laboratory. Sir David King, the chief scientific adviser, who will be reporting on the conference to Tony Blair, said: "This is the first time it [the research] has been pulled together. I think it is very serious."
Dr Carol Turley, the Plymouth laboratory's head of science, who presented the paper, said ocean acidification represented "potentially a gigantic problem for the world". She added: "It's urgent indeed to warn people what's happening. Many of the marine species we rely on to eat could well disappear. In cartoon terms, you could say people should prepare to change their tastes, and switch from cod and chips, to jellyfish and chips."
Remarkably, the findings about acidifying seas constituted the second revelation of a new global danger at the conference, which was called by the Prime Minister as part of Britain's efforts to focus attention on climate change during the UK presidency of the G8 group of rich nations and the European Union. On Tuesday, the head of the British Antarctic Survey, Professor Chris Rapley, disclosed that the vast West Antarctic ice sheet, previously thought to be stable, may be beginning to disintegrate, which would cause a sea-level rise around the world of more than 16ft. Although a growing number of studies about ocean acidification have been done, it is only recently that the whole picture has been put together, and stark nature of the threat appreciated. "The world scientific community is only just waking up to this," said Dr Turley, who with her colleagues has spent weeks briefing senior scientists on the problem in a range of government bodies from English Nature to the Department of Trade and Industry.
The world's oceans have always taken up and given off large volumes of naturally occurring carbon dioxide as part of the carbon cycle. But since the Industrial Revolution, the amounts have greatly increased, now more rapidly. The scientists believe 400 billion tons of man-made CO2 - half that produced - have been taken up by the seas, and much more is going in as the world economy relentlessly expands.
But the extra volumes are now causing a simple chemical reaction with the seawater - "O-level chemistry," Dr Turley said - in which the CO2 and the water (H2O) react to produce carbonic acid (HCO3). This is changing the chemical composition of the sea from slightly alkaline to acidic, producing an environment in which many vital organisms may not survive.
If, for example, the plankton on which cod larvae feed disappear, the cod will go, and something else, perhaps jellyfish, will move into their niche in the ecosystem.
Trials on organisms grown in seawater with raised CO2 levels, from plankton to scallops, indicate many species are likely to be affected. The increasing acidification is affecting coral already and another paper at the conference suggested that in 30 years all the world's coral reefs may be dying because of it.
The conference closed last night, with a statement saying: "In many cases, the risks are more serious than previously thought. This is likely to affect the entire marine food chain."
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