The researchers say governments must take action now to reduce the emissions of gases such as carbon dioxide, which are thought to be behind a rise in average global temperatures.

A slight rise in temperature can bleach coral like this

The scientists combined their coral expertise with the latest climate models to project what is likely to happen to the world's greatest reefs if global warming remains unchecked. Their study suggests the unique marine environments will increasingly become victim to a process known as coral bleaching.

A slight rise in maximum water temperatures - only one to two degrees - can stress the corals. This causes them to expel the microscopic organisms, known as zooxanthellae, which colour their tissues and provide them with essential nutrients.

If they zooxanthellae do not return, the corals will die. In 1998, the warmest year on record, every reef system in the world's tropical oceans was affected by some degree of bleaching. The report says the frequency and intensity of bleaching is set to rise.

Lost billions

The report's lead author is Professor Ove Hoegh-Guldberg, an expert on coral bleaching at Sydney University.

"Coral reefs could be eliminated from most areas of the world by 2100," Even the world's largest reef - the Great Barrier Reef off Australia - could be dead within 30 years unless measures are taken now to slow climate change.

The Great Barrier Reef could be dead within 30 years, the scientists warn

The professor says this would also devastate tourism and fishing industries which generate billions of dollars for their local economies each year.

Even if governments act to bring down greenhouse gas emissions, he says, it could still take up to 500 years for the reefs to recover.

Professor Hoegh-Guldberg's report has been released through the environmental group Greenpeace. It says the study underlines the need to phase out the burning of fossil fuels, the prime suspect for global warming.

"Government and industry must begin to switch to renewable energy now while there's still time to stop major climate change," says the organisation's climate campaigner Stephanie Tunmore.

The coral bleaching report will be published in the 50th anniversary issue of CSIRO's international science journal, Marine and Freshwater Research, in November.