Global warming threatens Australia's Barrier reef

CANBERRA (Reuters) - From a boat at sea, Australia's Great Barrier Reef seems invincible -- its myriad corals stretching 2,300 kilometers (1,400 miles) beyond sight.

But the reef's vastness and wave-smashing outcrops mask fragility in the face of climate change threatening to bleach its fluorescent depths the stark white of death.

The reef, and possibly the A$5.8 billion ($4.5 billion) tourist industry it underpins, will be "functionally extinct" by 2050, a draft report by the Intergovernmental Panel on Climate Change (IPCC) warned this week.

"Climate change is clearly a threat to the corals and the tiny plants that live in the tissues, but the issues go far beyond coral. Corals build a structure in which thousands of species live," Professor Ove Hoegh-Guldberg, a coral bleaching researcher, told Reuters.

Coral bleaching due to rising temperatures has struck many reefs around the world, hitting the Indian Ocean, parts of the Caribbean and Australia.

It occurs when corals living at the edge of their temperature tolerance expel the tiny animals that live inside, turning colorless and exposing their calcium skeletons inside.

Death follows unless the water soon cools. Global warming bringing temperature rises of between 2 to 3 Celsius (3.6 to 4.8 Fahrenheit) makes future salvation less likely.

"Coral bleaching can occur for a number of different reasons. But more recently, its been occurring because the seas in the tropical parts of the world are becoming too warm," Hoegh-Guldberg said.

Climatologists say Australia is suffering an "accelerated climate change", making the Great Barrier Reef's World Heritage corals at particular risk.

The reef is home to more than a third of the world's soft corals, more than 1,500 species of fish and six of the world's seven marine turtle species.

Indian Ocean corals were harder hit than Australia's in 1998, with 50 percent dying along its western rim in months.

"But of course we're only in the early days of climate change and it's of great concern that we've been seeing the type of increase in bleaching in severity and frequency that we've seen in other parts of the world," Hoegh-Guldberg said.

The new Australian of the Year, scientist and climate warrior Tim Flannery, said a new IPCC report on climate change blaming humans for rising global temperatures underestimated the speed of climate change, warning its findings were conservative.

"The actual trajectory we've seen in the arctic over the last two years if you follow that, that implies that the arctic ice cap will be gone in the next 5 to 15 years," Flannery told Australian radio.

"There's a 10 per cent chance of truly catastrophic rises in temperatures, so we're looking there at 6 degrees (Celsius) or so, that would be a disaster for all life on earth."

($1=A$1.29)