The Great Barrier Reef will be irreversibly damaged by climate change in just 16 years, according to leading reef researcher Ove Hoegh-Guldberg.
The reef has lost about half its coral coverage since the mid-1980s, with increased carbon dioxide concentrations contributing about 10 per cent alongside damage from other sources such as invasive species and farm nutrient run-off, Professor Hoegh-Guldberg, a professor of marine science at the University of Queensland, said.
Climate change, though, is fast taking over as the main threat to the world's reefs as warmer waters increase the frequency of coral bleaching, while acidifying oceans weaken or erode coral structures.
The reef's plight will be a focus of this year's Earth Hour, expected to be observed in 152 nations around the world.
By 2030, on present projections for the growth of carbon dioxide emissions, conditions will be "getting close to what we understand to be some of the limits in terms of rapidly calcifying reefs", Professor Hoegh-Guldberg said.
By mid-century, the Great Barrier Reef may have shrunk to 10 per cent or less of its previous coverage if the present trajectory continues, he said. A new report, Lights out for the reef, by University of Queensland scientist Selina Ward also highlights the potential ecological and economic damage to the reef from global warming.
Not only will shrinking coral reefs diminish the annual $6 billion reef tourism industry and the 63,000 jobs it supports, there will be other impacts, the report said. "One of the most important functions of the reef is as a wave barrier. That protection will be lost," Dr Ward said. "Without the reef, a lot of islands will be swamped."
The report, issued to coincide with the relaunch of Earth Hour for March 29, details the ways climate change is weakening the reef.
Bleaching, for instance, is caused by corals becoming too warm and dying at a much greater rate than normal - a process unknown in Great Barrier Reef before 1979.
And heat-stressed corals are now more likely to succumb to disease after a bleaching event because the role of bacteria is changing. "In good times, the bacteria acts as an antibiotic," Dr Ward said. "After a heat event, that effect is lost."
Recent research shows the erosion of the reef from acidification as more carbon dioxide is absorbed by the oceans is happening more rapidly than previously thought, she said.
The biennial State of the Climate report, released this week by the Bureau of Meteorology and CSIRO, found sea-surface temperatures in the Australian region had risen 0.9 degrees since 1900. Temperatures last year were 0.5 degrees above the 1961-90 average. Ocean acidity had risen about 26 per cent since 1750, the report said.