Australia's iconic and beloved Great Barrier Reef will be destroyed by erosion and swamped by invading algal slime within 40 years if current global warming trends continue, new research suggests.
The research shows climate change has dramatically slowed growth rates of Porites or brain corals one of the biggest corals forming the reef's structure sparking fears the reef will ''stop growing altogether'' by 2050.
Scientists from the Australian Institute of Marine Science in Queensland said the study showed the reef, which pumps more than $5billion a year into Australia's economy from tourism, had already reached its ''tipping point'' in response to global warming.
The institute's principal researcher, Glenn De'ath, said the ''sharp and sudden'' drop in coral growth rates had occurred across the reef, ruling out the possibility it could be a localised impact linked to poor water quality caused by urban and agricultural run-off.
''What we're seeing isn't a localised problem that's occurring in one or two places. The decline in coral growth rates is spread right across the length and breadth of the reef,'' he said.
In an online opinion piece for The Times newspaper in London, BBC marine archaeologist Frank Pope said the news that climate change was slowing the growth of ''the world's largest biological structure, the only one visible from space ... should send shivers down our spine''.
The findings, published yesterday in the global journal Science, revealed coral calcification rates had dropped by more than 14 per cent since 1990.
This had been caused by a combination of warming sea surface temperatures and ocean acidification.
The Greens have urged the Rudd Government to respond to the serious implications of the institute's research by revising its recently announced target to cut greenhouse emissions by 5 per cent by 2020.
Greens climate change spokeswoman Rachel Siewert said, ''These research findings confirm the target is way too low to be effective. We don't have near as much time as we thought we had to save the reef from dangerous climate change. It's already here.''
A spokesman for Environment Minister Peter Garrett said the Government was ''taking immediate action to improve the Reef's resilience'' by investing $200million in a reef rescue plan and a further $8.9million to support a five-year climate change action plan.
Dr De'ath said a study by institute scientists of more than 320 coral samples from 69 reefs across the Great Barrier Reef showed growth rates were at their lowest level in 400 years.
''The big corals, the brain corals, have slowed their growth by more than 14 per cent since 1990, which is a sudden and severe decline in calcification that's unprecedented over the past 400 years,'' he said.
''If that trend continues, we will see a complete change in the reef's physical structure and the biodiversity it can support. Corals provide habitat for lots of little fish and if you lose those little fish, you lose the big ones that feed on them and the ecosystem gradually collapses.''
Reef corals create a hard skeleton from materials dissolved in seawater, and when large amounts of atmospheric carbon dioxide are absorbed by the ocean, chemical changes reduce the ability of marine organisms to calcify, or form skeletons.
One of the co-authors of the Science paper, reef ecologist Janice Lough, said it was ''cause for extreme concern'' that such changes in coral growth rates were already evident, ''with the relatively modest climate changes observed to date'' on one of the world's best-protected coral reef ecosystems.
An analysis of annual growth bands similar to tree rings in the coral samples shows modest fluctuations in calcification until 1990, with an annual decline that year of 0.3 per cent.
Dr De'ath said, ''If you take that current trend to its logical conclusion, the corals will stop growing altogether by 2050.'' He said the reef was ''in for a pretty rough ride'' if governments did not act quickly to reduce carbon dioxide levels in the atmosphere.
''Although it is good to see some mechanisms in place to cut greenhouse emissions, we really need to achieve much greater reductions if we want to see the reef to survive,'' he said. ''If you consider some of the findings of the Garnaut report [on climate change in Australia], on a per capita basis, Australia is the world's No1 greenhouse polluter. We consume and generate carbon dioxide on a per capita basis at a level that is three times the OECD average.
''Given those figures, if we want the reef to stick around, it would be a good idea to reduce our dependence on fossil fuels and think about shifting to solar energy.''