The government agency responsible for the Great Barrier Reef says urgent action is needed to save the world heritage site after yet-to-be-published surveys found the record coral bleaching damage earlier this year was even worse than initially thought.
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A Great Barrier Reef Marine Park Authority director also says it appears unlikely that national targets to improve water quality on the reef - currently assessed as poor in areas close to the coast - would be met.
Authority director for reef recovery David Wachenfeld said pressures on the reef were increasing, particularly due to global warming, but that the reef could be returned to health through concerted effort by industry, the community and governments.
"People need to be determined. This is the time to act to save the Great Barrier Reef," he said.
While reef surveys are yet to be completed, Dr Wachenfeld said the rate of coral death following bleaching due to high ocean temperatures last summer would be greater than the initial estimate of 22 per cent.
"Essentially, this is confirming that this is the worst bleaching event that the reef has seen by a very, very long way," he said.
The bleaching was not uniform. Inner and middle shelf reefs north of Port Douglas were badly affected, but southern reefs were barely touched after the tail-end of cyclone Winston reduced temperatures in February.
Dr Wachenfeld, a trained coral reef ecologist, said the damage was unquestionably linked to climate change.
"It just re-emphasises ... the absolutely critical need for us to implement the climate agreement that was reached in Paris a year ago," he said.
Federal Environment Minister Josh Frydenberg met with his Queensland counterpart Steven Miles on Friday to finalise an update to the UNESCO World Heritage Centre on progress in improving the reef's health.
The United Nations body last year decided against listing the reef as "world heritage in danger", and gave the government five years to halt its deteriorating health. The Australian government is due to update the centre by December 1.
The ministers announced $45 million funding to reduce gully erosion, which dumps sediment into rivers that empty on to the reef.
Mr Frydenberg said the governments were "only getting started" on improving the plight of the reef, and that climate change was a factor. But he said Australia was doing its part under the Paris deal by setting a target to cut emissions by 26-28 per cent emissions by 2030.
"I'm very confident with the mechanisms we have in place that, despite that bleaching event, the Barrier Reef will continue to remain strong, healthy, resilient for future generations of Australians," he said.
Mr Frydenberg said the coral death due to bleaching followed a 19 per cent increase in cover in recent years.
But Terry Hughes, head of the ARC Centre of Excellence for Coral Reef Studies, said the minister appeared to have misinterpreted a report by the Australian Institute of Marine Science that found there had been a 3.2 per cent increase in coral before the bleaching event.
In the north, the area worst hit, the coral cover had actually declined by 4.8 per cent before being affected by bleaching.
Professor Hughes said the most likely scenario was that the next serious bleaching event would be in about five years, when climate change combined with the next El Nino event to inflate Pacific Ocean temperatures.
"We could be lucky and it could be later, or it could be sooner," he said. "By 2030, under business as usual emissions, we could see annual bleaching events."
Dr Wachenfeld said the reef remained one of the best protected marine ecosystems in the world and was "very, very far from dead". But it would be dramatically changed under projections based on existing climate pledges of 2.8 degrees global warming this century.
"At that temperature it doesn't look anything like it does today," he said. "There will be very little coral left, it will have lost a lot of its biodiversity and, in particular, it will have lost its value to people."
Poor water quality, largely due to agricultural run-off, is considered the second biggest threat facing the reef. Estimates of the cost of addressing it range from $8.2 billion to $10 billion.
Dr Wachenfeld said governments and farmers started working on improving water quality 13 years ago and should be proud of their early progress, but results had tailed off.
"We still haven't met the targets that we set ourselves and on our current trajectory it doesn't look like we will," he said. "And some of the progress on reducing pollutants has kind of flatlined."
Targets include a 50 per cent cut in nitrogen run-off from fertiliser use by 2018, increasing to 80 per cent by 2025. Nitrogen is linked to outbreaks of crown-of-thorns starfish, which feed on coral.
A government report card released last month based on 2015 data found the inner reef area was in poor condition.
An analysis by environment groups under the banner Fight for the Reef found Australia had made progress on some of its commitments to UNESCO - banning sea-dumping of industrial dredge spoil and limiting port development - but had fallen behind on others.
They said the country risked being called back before the World Heritage Committee next year unless it did more to stop tree clearing, improve water pollution and lifted its response to climate change.
Legislation to reduce tree clearing recently failed to pass the Queensland Parliament after being blocked by the Liberal National Party and crossbenchers.
