The Great Barrier Reef could become "functionally extinct" within decades, according to a report leaked today. Image: NASA

SYDNEY: Australia's famed Great Barrier Reef, the world's largest living organism, could be killed within decades by global warming, scientists warned in a report leaked today.

The World Heritage site, stretching over more than 345,000 square kilometres off the northeast Australian state of Queensland, will soon become "functionally extinct", the scientists are quoted as saying in The Age newspaper.

Their assessment is contained in a leaked draft of a major international report by the U.N. Intergovernmental Panel on Climate Change (IPCC) to be released later this year, the newspaper said.

Some 500 climate change experts from around the globe are meeting in Paris this week, ahead of the release on Friday of the first volume of the IPCC's fourth report on climate change. The report is the first from the body since 2001 on the state of scientific knowledge on global warming.

The report will be followed in April by volumes focussing on the impacts of climate change and on the social-economic costs of reducing the emission of greenhouse gases blamed for global warming.

A chapter on Australia in these volumes warns that deadly coral bleaching in the Barrier Reef is likely to become an annual occurrence by as early as 2030 due to warmer, more acidic seas.

Coral is made up of millions of tiny animals, called polyps, that contain and depend on tiny plant-like organisms called algae. The polyp creates a limestone cocoon around itself and uses tiny tentacles to filter plankton from passing water. The algae uses sunlight to make food through photosynthesis, which it and the polyp share. Bleaching occurs when the algae dies - causing the death of the polyp and leaving behind the white limestone skeleton of the reef.

The IPCC panel is highly regarded for its neutrality and caution, and wields great influence over government policies and corporate strategies. Earlier warnings that climate change was damaging the reef, a major tourist attraction, prompted the Australian government to announce late last year that it was considering using vast sunshades to protect the coral.

Australia's tourism Minister Fran Bailey said the government was looking at funding the use of shade cloths to protect vulnerable parts of the giant reef, after a promising two-year trial. The cloth, which is being developed by marine researchers in Queensland, would be held in place by floating pontoons.

Marine biologist Russell Hore, from Reef Biosearch in Port Douglas, said while the sun shade idea had at first seemed laughable, everything had to be considered to protect the reef.