How global warming sealed the fate of the world’s coral reefs

Destroyed by rising carbon levels, acidity, pollution, algae, bleaching and El Niño, coral reefs require a dramatic change in our carbon policy to have any chance of survival, report warns

Animal, vegetable and mineral, a pristine tropical coral reef is one of the natural wonders of the world. Bathed in clear, warm water and thick with a psychedelic display of fish, sharks, crustaceans and other sea life, the colourful coral ramparts that rise from the sand are known as the rainforests of the oceans.

And with good reason. Reefs and rainforests have more in common than their beauty and bewildering biodiversity. Both have stood for millions of years, and yet both are poised to disappear.

Remember the carbon dioxide that we left dissolving in the oceans? Billions and billions of tonnes of it over the last 150 years or so since the industrial revolution? While mankind has squabbled, delayed, distracted and dithered over the impact that carbon emissions have on the atmosphere, that dissolved pollution has been steadily turning the oceans more acidic. There is no dispute, no denial, about this one. Chemistry is chemistry, and carbon dioxide plus water has made carbonic acid since the dawn of time.

As a result, the surface waters of the world’s oceans have dropped by about 0.1 pH unit – a sentence that proves the hopeless inadequacy of scientific terminology to express certain concepts. It sounds small, but is a truly jaw-dropping change for coral reefs.

For reefs to rebuild their stony skeletons, they rely on the seawater washing over them to be rich in the calcium mineral aragonite. Put simply, the more acid the seawater, the less aragonite it can hold, and the less corals can rebuild their structure. Earlier this year, a paper in the journal Science reported that calcification rates across the Great Barrier Reefs have dropped 14% since 1990. The researchers said more acidic seas were the most likely culprit, and ended their sober write-up of the study with the extraordinary warning that it showed “precipitous changes in the biodiversity and productivity of the world’s oceans may be imminent”.

David Adam,, 2 September 2009. Full article.

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