One fifth of reefs are dead and the remainders under threat, according to a new report.

Credit: Wikimedia

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The Great Barrier Reef could be lost within our lifetime, if a new report from the Global Coral Reef Monitoring Network is to be believed.

The report shows the world has already lost 19 per cent of its coral reefs, and the rest are under threat from climate change. If current trends in carbon dioxide emissions continue, many of the remaining reefs may be lost over the next 20 to 40 years.

The Great Barrier Reef is worth an estimated $5.1 billion to the Australian economy through tourism.
Climate change is considered the biggest threat to coral reefs today. The main climate threats, including increasing sea water temperatures and seawater acidification, are being exacerbated by other threats including overfishing, pollution and invasive species.

"If nothing changes, we are looking at a doubling of atmospheric carbon dioxide in less than 50 years," says Carl Gustaf Lundin, Head of the IUCN Global Marine Program, one of the organisations behind the Global Coral Reef Monitoring Network. "As this carbon [dioxide] 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."

Encouragingly, 45 per cent of the world's reefs are currently listed as "healthy". Another sign of hope is the ability of some corals to recover after major bleaching events. Coral bleaching occurs when the colourful zooxanthallae residents of the corals abandon their home when stressed by warming waters.

However, the report shows that, globally, the outlook is still grim. Major threats in the last four years, including the Indian Ocean tsunami, more occurrences of bleaching, outbreaks of coral diseases and ever-heavier human pressures, have slowed or reversed recovery of some coral reefs after the 1998 mass bleaching event.

"The report details the strong scientific consensus that climate change must be limited to the absolute minimum. If nothing is done to substantially cut emissions, we could effectively lose coral reefs as we know them, with major coral extinctions," says Clive Wilkinson, coordinator of the Global Coral Reef Monitoring Network.

Corals have a higher chance of survival in times of climate change if other stress factors related to human activity are minimised. Well-managed marine protected areas, such as the Great Barrier Reef can also boost the health of coral reefs, but proper enforcement is difficult, especially in remote areas where the most pristine reefs are found.

"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," says David Obura, Chair of the IUCN Climate Change and Coral Reefs working group and Director of the Coastal Oceans Research and Development in the Indian Ocean Programme (CORDIO) in East Africa.

A new report on the state of Indian Ocean coral reefs, also launched today, states an overall trend of continued degradation, only alleviated by signs of recovery in some areas.