Reefs in hot water as climate changes

HALF of the world’s coral reefs, known as the ‘ocean’s rainforests’, could be wiped out or damaged by the end of the century due to the destructive effects of climate change.

Leading scientists have warned there is now irrefutable evidence that these natural wonders of the world are being irreparably damaged in a way that will have a serious impact on communities all over the world, who rely on them as both a source of food and protection against natural disaster.

Dr Richard Aronson, who has helped compile the most definitive study yet on the impact of global warming on reefs, said that in his own lifetime stunning underwater landscapes in the Caribbean now "looked like hell" and that this was being replicated around the world.

About 25% of the world’s coral have already been wiped out or extensively damaged by warming oceans, pollution and disease - all of which have been linked to human activity.

If nothing is done to resolve the problem, a further 30% could suffer the same fate in years to come, said Aronson, from the Dauphin Island Sea Laboratory in Alabama in the US. "More than half will be ruined or degraded by 2100."

The study, released at the American Association for the Advancement of Science’s annual meeting in Seattle this weekend, identified the direct and knock-on effects of global warming on coral reefs, showing that climate change endangers them directly in two important ways.

Warmer temperatures have had the indirect effect of allowing harmful diseases to flourish, which have been further encouraged by man-made pollutants that nourish bacteria and fungi running off the land into the sea.

Aronson said an increase in temperature of even one or two degrees centigrade could have a "devastating" impact on coral.

One key effect has been to heighten the impact of freak ‘El Nino’ events - disturbances in the Pacific ocean-atmosphere weather system that can have a major impact on climate around the world.

The El Nino of 1997-98, boosted by global warming, produced the hottest tropical temperatures ever recorded. That event alone destroyed 16% of the world’s coral.

"Global warming is ratcheting up the temperature of these El Nino events," said Aronson.

Dr Joan Kleypas, from the National Centre for Atmospheric Research in Boulder, Colorado, one of the report’s co-authors, said that although coral reefs had adjusted to periods of gradual warming in the past, the rate of change now taking place was unprecedented.

"These coral communities will be pulled apart," she said. "They’re not going to function well as coral reefs any more."

Higher water temperatures have also produced ‘bleaching’, where coral has been weakened and killed after losing the vital algae that live symbiotically within it. Secondly, as carbon dioxide builds up in the atmosphere, more of it dissolves into the oceans, making the water more acidic.

This has reduced the levels of carbonate that coral use to grow their skeletons and build up reefs.

Atmospheric carbon dioxide levels were about 280 parts per million in 1880. By 2000 they had increased to 367 parts per million, and by 2050 they are expected to reach 463 to 623 parts per million.

The report, ‘Coral Reefs & Global Climate Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems’, also highlights the enormous impact the destruction of coral reefs has on communities around the world. It is estimated that tens of millions of people depend on reefs, both as a food source and because of the way they prevent erosion of tropical shorelines.

Coral reefs are believed to generate a total annual income of around 16bn.

Aronson said that even in his lifetime, the Caribbean reefs he knew as a child had changed beyond recognition. "If you go around the Caribbean today, the coral reefs look like hell, they’re horrendous," he said.

"It’s happening. There’s no escaping the consequences. Coral reefs are being damaged by climate change."

The world’s largest living structure, Australia’s Great Barrier Reef, has already come under the spotlight, with a report warning global warming could devastate it in the next 50 years if action is not taken now.

The Australian Institute of Marine Science and other agencies said that, without tough restrictions on greenhouse-gas emissions, sea temperatures could rise to a level that would bleach and kill vast tracts of coral.

The Great Barrier Reef spans almost 135,000 square miles along Australia’s north-east coast. It is also threatened by overfishing and pollution. In June last year the federal government proposed making 30% of the reef a marine sanctuary. Currently only 4.5% is protected. The reef is worth almost 1m a year to the Australian economy.