Gigantic changes to the world's oceans, leading to the complete disappearance of marine life from cod to coral reefs, are now threatened by the main greenhouse gas causing global warming, British scientists warned yesterday.
Researchers sounded the alarm about a completely new and potentially devastating danger to the world from the huge volumes of carbon dioxide (CO2) produced by industry and transport, which is already known to be threatening the future of the planet by changing the climate.
Now, they said, it is also rapidly turning the world's oceans acid as it is dissolved in sea water, 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 right up the chain, through shellfish to major human food species such as cod.
It is already known to be having a serious impact on some organisms such as coral, and putting a question mark against the whole future of coral reefs.
The findings about acid seas, which are very recent, are causing alarm in the international scientific community as they represent a genuinely major threat to the world that has hitherto been completely unappreciated.
They were set out in detail at the conference on climate change being held at the UK Met Office headquarters in Exeter, in a paper by a team of scientists from Britain's Plymouth Marine Laboratory.
Sir David King, the Government's Chief Scientific Adviser, who will be reporting on the conference to Tony Blair, the British prime minister, singled out the importance of their account.
"This is the first time it has been pulled together," he said. "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 said: "It's very urgent indeed to warn people what's happening. Many of the marine species we rely on to eat could well disappear and replaced by others. In cartoon terms, you could say that 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 personally by Mr Blair as part of Britain's efforts to focus attention on climate change during the UK presidency both 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 - an event that would cause a sea-level rise around the world of more than sixteen feet.
Although a growing number of studies about ocean acidification have been carried out in recent years, it is only very recently that the whole picture has been put together, and truly 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 recent 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 what is known as the carbon cycle.
But since the industrial revolution the amounts have hugely increased, and are rapidly increasing still. It is estimated that about 400bn tonnes of man-made CO2 - half that ever produced - have been taken up by the seas, and much more is going in as the world economy relentlessly expands.
However, the extra volumes are now causing a very simple chemical reaction with the sea water - "O-level chemistry," Dr Turley said - in which the CO2 and the water (H2O) react to produce carbonic acid (HCO3).
This is changing the basic chemical composition of the sea, which is slightly alkaline, to acidic, and producing an environment in which many tiny but vital organisms such as plankton may not be able to survive.
If, for example, the plankton on which cod larvae feed disappear, the cod will go too, and something else - such as jellyfish - will move into their niche in the ecosystem.
Trials on organisms grown in sea water with raised CO2 levels, from plankton to scallops, indicate that large numbers of species are likely to be affected. "The whole composition of life in the oceans will change," Dr Turley said.
The increasing acidification is known to be affecting coral already and another paper presented to the conference suggested that in as little as thirty years all the world's coral reefs may die because of it.
The conference, which closed last night, suggested in its formal conclusions that the threat from climate change now appeared greater even than in the last report of the UN's Intergovernmental Panel on Climate Change, which was published only in 2001.
"In many cases, the risks are more serious than previously thought," said the closing statement.
It added: "A number of new impacts were identified that are potentially disturbing. One example is the recent change that is occurring in the acidity of the ocean. This is likely to affect the entire marine food chain."