Scientists warn acid is killing oceans

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Rising carbon dioxide emissions are turning the oceans acidic in an irreversible process that threatens coral reefs and food security, the world’s scientific academies have warned.

Seventy academies, including the Australian Academy of Science, urged governments meeting in Bonn for climate talks to tackle the issue in the new United Nations treaty on climate change to be agreed in Copenhagen in December.

In the past 200 years the world’s oceans have absorbed about a quarter of the carbon dioxide produced by human activities, and the current rate of acidification is much more rapid than at any time during the past 65 million years, the scientists said in a joint statement.

Martin Rees, president of the Royal Society in Britain, said that unless global carbon dioxide emissions were cut by at least 50 per cent of 1990 levels by 2050 there could be an “underwater catastrophe” and loss of marine life.

“The effects will be seen worldwide, threatening food security, reducing coastal protection and damaging local economies that may be least able to tolerate it,” Professor Rees said. “Copenhagen must address this very real and serious threat.”

As carbon dioxide dissolves it alters ocean chemistry, leading to an attack on the carbonate building blocks needed by marine organisms, such as corals and shellfish, to produce their skeletons, shells and other hard structures.

“Ocean acidification is irreversible on timescales of at least tens of thousands of years,” the scientists said.

Although it was a global problem, some areas, including the tropical waters around the Great Barrier Reef, would be more affected than others.

Terry Hughes, director of the Australian Research Council Centre for Coral Reef Studies at James Cook University, said the effects have already been observed. “We have clear evidence that the growth rate of corals is slowing because of ocean acidification.”

The Great Barrier Reef was under stress as well from higher water temperatures, said Professor Hughes, who contributed to the academies’ statement.

“Unless the world can sharply reduce greenhouse gas emissions, the combination of repeated bouts of bleaching, more extreme storms and slower growth due to acidification will have a severe impact on coral reefs and the tourism and fisheries industries they support,” he said. “We only have a narrow window of opportunity to prevent further severe damage to coral reefs before it’s too late.”

Will Howard, an oceanographer at the Antarctic Climate and Ecosystems Co-operative Research Centre in Hobart, said the issue of acidification was independent of debates about possible effects of global warming.

“The impact is happening now in nature, not in computer simulation or in laboratory manipulation, and can be directly attributed to carbon dioxide emissions,” Dr Howard said.

If carbon dioxide levels, now at 387 ppm, were stabilised at 450 ppm, more than 10 per cent of the world’s oceans would be affected by acidification, including more than 90 per cent of all tropical and subtropical coral reefs.

Stabilisation at 550 ppm could result in coral reefs “dissolving globally”, the scientists said.

Adding chemicals to the oceans to try to counter acidification was likely to be expensive, only partly effective at local sites and could pose unknown risks.