Most of the world's coral reefs are doomed to perish during the next century according to a new report on global warming.

Michael Peschardt reports on the danger threatening the coral reefs

The report, carried out by Sydney University Professor Ove Hoege-Guldberg, warns that tropical marine environments are likely to be the first casualties of climate change.

He predicts that reefs in the Central Pacific area may last until 2050 - but that others have a far shorter shelf life.

"Reefs around the West Indies in the Caribbean look as though they will be gone by 2020 while the Great Barrier Reef will probably last for just another three decades," he warned.

The dying reef is a "canary in a cage" warning

The reason for the pessimism can be found under the water around most of the world's great reef systems. On the Great Barrier Reef, for instance, increasing areas of coral are dying.

The normally bright vibrant colours are disappearing and in their place the coral has turned a deathly pale.

The plant cells in coral are unable to cope with rising temperatures and once they begin to falter the entire coral system loses its central core and the fish that normally live there are forced away eventually to starve.

It is a profoundly depressing sight.

Freak weather

Scientists at the Great Barrier Reef Marine Authority in Townsville have also been tracking the problem.

Coral reefs attract lots of tourist revenues

Dr Jamie Oliver, speaking from the authority's headquarters, highlighted the freak weather conditions, which have been effecting coral systems.

He said that there had been a band of warm water right across the Indian Ocean, the Maldives and the Seychelles.

"American satellite systems had picked up a wall of water two or three degrees warmer than usual sitting across much of the coral reef area of the world causing stress from heat. So what we have seen is stress right across the tropical band."

Last year is thought to have been the warmest in terms of sea temperature for 400 years.

If it is repeated again the prospects look especially bleak.

Australian Green Peace spokesman, Irwin Jackson, said that "coral reefs are now in effect the canaries in the cage, warning the world that something must be done to limit carbon emissions and slow down global warming."

It is more than just an environmental crisis it is a human one as well.

One and half million people visit Australia's Great Barrier Reef each year spawning a thriving local economy. If the reef dies, thousands face losing their livelihoods as the tourist industry crumbles.

International action demanded

John Tanzer of the Great Barrier Reef Marine Authority is calling on international action to care for the reef.

The entire ecosystem is under threat

He said: "If the world doesn't care about a natural wonder like the Great Barrier Reef, it fails to care about the fact that we live off the environment.

"The environment isn't something out there. It feeds and clothes us. If we don't care about the Great Barrier Reef we don't care about our future," he said.

The Great Barrier Reef is said to be the only natural structure clearly visible from space.