The World Heritage site, stretching over more than 345,000 square kilometers (133,000 sq miles) off Australia's east coast, will become "functionally extinct", the scientists are quoted as saying in The Age newspaper.

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

A chapter on Australia in the report on global impacts of climate change warns that coral bleaching in the Barrier Reef is likely to become an annual occurrence by as early as 2030 due to warmer, more acidic seas.

Bleaching occurs when the plant-like organisms that make up coral die and leave behind the white limestone skeleton of the reef.

Some 500 experts are meeting in Paris this week ahead of the release on Friday of the IPCC's first report since 2001 on the state of scientific knowledge on global warming.

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

The panel is highly regarded for its neutrality and caution, and wields a big 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.

Tourism Minister Fran Bailey said the government was looking at funding the use of shade cloths to protect vulnerable parts of the giant reef off the coast of Queensland state, after a promising two-year trial.

The cloth, which is being developing 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 idea had at first seemed laughable, everything had to be considered to protect the reef.

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