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Acidic seas pose a threat to coral reefs

London: The majority of the world’s coral reefs are in danger of being killed off by rising levels of greenhouse gases, scientists warned on Thursday.

Researchers from Britain, the U.S. and Australia, working with teams from the U.N. and the World Bank, voiced their concerns after a study revealed 98 per cent of the world’s reef habitats are set to become too acidic for corals to grow by 2050.

The loss of major coral reefs would have a devastating effect on local communities, many of which rely heavily on fish and other marine life that shelter among the reefs.

The destruction of reefs would leave coastlines unprotected against storm surges and affect often crucial income from tourism. Among the first victims of acidifying oceans will be Australia’s Great Barrier Reef, the world’s largest organic structure.

Each year, more than 20 billion tonnes of carbon dioxide are released into the atmosphere by human activity. Around a third of this is absorbed by the oceans. While the process helps slow global warming by keeping the gas from the atmosphere, in sea water it dissolves to form carbonic acid.

Rising levels of carbonic acid in sea water cause carbonates to dissolve. One of these minerals, aragonite, is used by corals and other marine organisms to grow their skeletons, but it is particularly susceptible to carbonic acid. Without it, corals become brittle and are unable to grow and repair damage caused by fish, snails and natural erosion.

The scientists used computer simulations to model levels of aragonite in the world’s oceans from pre-industrial times, when atmospheric carbon dioxide levels stood at 280 parts per million. Present day levels of carbon dioxide are 380 ppm, but scientists expect the figure will rise substantially by the end of the century. The team looked at different scenarios based on predictions of greenhouse gas emissions by the UN’s Intergovernmental Panel on Climate Change.

In the worst scenario, when carbon dioxide levels rose above 500 ppm, the models predicted a temperature rise of 3C and a substantial increase in ocean acidity, causing the majority of reefs to crumble and die off, with only some of the most robust corals surviving. The study appears in the journal Science. —

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