Coral die-off
© AFPAn environmental management specialist of the Batangas city fisheries office inspects a coral reef formation in the Verde sea passage south of Manila, Philippines, February 2007.
Poznan, Poland - Almost a fifth of the planet's coral reefs have died and carbon emissions are largely to blame, according to an NGO study released Wednesday.

The report, released by the Global Coral Reef Monitoring Network, warned that on current trends, growing levels of greenhouse gases will destroy many of the remaining reefs over the next 20 to 40 years.

"If nothing is done to substantially cut emissions, we could effectively lose coral reefs as we know them, with major coral extinctions," said Clive Wilkinson, the organisation's coordinator.

The paper was issued on the sidelines of the December 1-12 negotiations on a new global treaty on climate change, taking place under the UN flag.

Half a billion people around the world depend on coral reefs for food and tourism, according to a common estimate.

Experts say the coral die-off has several causes, including local pollution, overfishing and invasive species.

But, they say, rising ocean temperatures caused by the greenhouse effect, and acidification, caused by the ocean's absorption of carbon dioxide (CO2) from the atmosphere, are probably the biggest triggers.

"If nothing changes, we are looking at a doubling of atmospheric carbon dioxide in less than 50 years," said Carl Gustaf Lundin, head of the the global marine programme at the International Union for the Conservation of Nature, an umbrella network for more than a 1,000 NGOs and government groups.

"As this carbon is absorbed, the oceans will become more acidic, which is seriously damaging a wide range of marine life from corals to plankton communities and from lobsters to seagrasses."

Nearly half of global coral reefs are still healthy, but the overall downward trend shows no sign of stopping, the study found. It added, though, that the damage could be braked by strong conservation measures, such as properly policed marine parks.