Fifth of world's coral reefs dead, say marine scientists

Climate change linked to warmer and more acidic seas pose biggest threat to coral survival, says report

• David Adam, environment correspondent
• guardian.co.uk, Wednesday December 10 2008 17.00 GMT
• Article history

Plight of the coral reefs. Photograph: Cathie Page

A fifth of the world's coral reefs have died or been destroyed and the remainder are increasingly vulnerable to the effects of climate change, a new study says.

The Global Coral Reef Monitoring Network says many surviving reefs could be lost over the coming decades as CO2 emissions continue to increase.

"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 of the GCRMN.

The report, released today at UN climate talks in Poznan, Poland, said warmer and more acidic seas posed the biggest threat in future. Other threats include overfishing, pollution and invasive species – as well as natural hazards, such as the earthquake that triggered the Indian Ocean tsunami in 2004, which forced reefs from the water.

Corals are crucial to the livelihoods of millions of coastal dwellers around the world. The UN's Millennium Ecosystem Assessment says reefs are worth about $30bn annually to the global economy through tourism, fisheries and coastal protection.

"If nothing changes, we are looking at a doubling of atmospheric CO2 in less than 50 years," said Carl Gustaf Lundin, head of the International Union for Conservation of Nature's global marine programme, which is one of the organisations behind the GCRMN. "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."

The report found that some 45% of the world's reefs are currently healthy, and that some retain the ability to recover after major bleaching events, such as the one caused by the El Niño event in 1998, and to adapt to climate change threats. But, globally, the downward trend of recent years has not been reversed.

David Obura, chair of the IUCN climate change and coral reefs working group, said: "Ten years after the world's biggest coral bleaching event, we know that reefs can recover – given the chance. Unfortunately, impacts on the scale of 1998 will reoccur in the near future, and there's no time to lose if we want to give reefs and people a chance to suffer as little as possible."