Instead of the rich environment depicted in the recent movie Finding Nemo, the coral reef will be bleached out and replaced by ordinary seaweed, costing the tourism industry billions of dollars, a report into the impact of global warming says.

Authors Hans and Ove Hoegh-Guldberg - the head of Queensland University's marine studies centre and his economist father - spent two years examining the effects of rising sea temperature on the reef for Queensland tourism authorities and the World Wildlife Fund for Nature (WWF).

Their 350-page report found no prospect of avoiding the "chilling long-term eventualities" of coral bleaching because
greenhouse gases
were already warming the seas as part of a process it said would take decades to stop.

"Coral cover will decrease to less than 5% on most reefs by the middle of the century under even the most favourable assumptions," the report said.

"This is the only plausible conclusion if sea temperatures continue to rise."

Warmer sea waters make corals suffer thermal stress, eventually making them bleach and die.

Rising temperatures

Great Barrier Reef

Some facts

  • Covers more than 345,000sq km
  • Consists of 2900 interlinked reefs and 900 islands
  • Home to 1500 fish species

Loss

  • Coral cover to decrease to 5%
  • Economy to lose $6.24 billion
  • Around 12,000 jobs on the line
The report said this could occur if temperatures increased by as little as one degree centigrade, well below the two to six degrees water temperatures around the reef are expected to rise by over the next century.

"There is no evidence that corals can adapt fast enough to match even the lower projected temperature rise," it found.

Organisms reliant on coral would become rare or even face extinction, the report said.

It said the bleaching would cost the economy up to $6.24 billion and 12,000 jobs by 2020 under the worst-case scenario.

Even under the best case scenario, about 6000 jobs would be lost and tourists would be forced to visit "Great Barrier Reef theme parks" offshore to view the remaining coral.

The reef covers more than 345,000sq km off Australia's northeast coast, making it the world's largest coral reef.

Consisting of 2900 interlinked reefs, 900 islands and 1500 fish species, scientists consider it the world's largest living organism.

Environmental threat

Yet, the delicate habitat faces numerous environmental threats, including chemical run off from farms, over-fishing, bleaching and the parasitic Crown-of-Thorns starfish, which attacks coral.

The government announced plans in December to reduce farm run off and ban fishing in about a third of the reef in an effort to protect Australia's number one tourist drawcard.

But the report's authors said the government needed to do more, recommending Canberra ratify the Kyoto protocol on reducing greenhouse gases and take the lead in emission reduction.

The WWF said urgent measures must be put in place to minimise reef damage and reduce greenhouse gases.

"The argument for instant action is undeniable," WWF said in a statement.

"Major reductions in greenhouse gas emissions must occur now, not in five or 10 years time. This is likely to deliver major benefits to our societies both in the near-term and at times beyond 2050."