For the first time, the long-term outlook for the Great Barrier Reef has been downgraded from "poor" to "very poor" by the Federal Government's five-year reef report.
The evidence-based report written by the Great Barrier Reef Marine Park Authority (GBRMPA) using more than 1000 scientific reports was described by its chairman Ian Poiner as "sobering".
The report said climate change was escalating and was the most significant threat to the Great Barrier Reef's long-term survival.
"The current rate of global warming will not allow the maintenance of a healthy reef for future generations," the report said.
Experts said strong mitigation actions "within the next decade" would be necessary to achieve the best possible outlook for the reef and future generations.
"Specifically, early and effective global and national action on climate change, coupled with local actions to ... facilitate recovery, are imperative over the next 10 years if the region is to have a positive long-term outlook.
"The scientific evidence is clear: initiatives that will halt and reverse the effects of climate change at a global level and effectively improve water quality at a regional scale are the most urgent," the report said.
According to the report, "without additional local, national and global action on the greatest threats, the overall outlook for the Great Barrier Reef's ecosystem will remain very poor, with continuing consequences for its heritage values also".
"The challenge is big, but not insurmountable - actions taken now will matter."
The downgraded outlook status comes after back-to-back coral bleaching events, cyclones and record-breaking warm water - particularly affecting the northern part of the reef, which had previously been considered to be pristine.
"Even with the recent management initiatives to reduce threats and improve resilience, the overall outlook for the Great Barrier Reef is very poor," said Mr Poiner.
The reef is expected to continue to deteriorate, which experts say will only change if there is an urgent and coordinated action to cut greenhouse gas emissions.
The findings come on the same day the Federal Government released its quarterly emissions data for the first three months of 2019. It showed that pollution for the year to March rose by 0.6 percent.
Australian emissions have risen for five years in a row.
The report found there was a "multi-tiered governance and management regime" to protect the reef's biodiversity, ecosystem and heritage values, "however this regime is not designed to directly address the effects of a changing climate".
"Climate change remains the greatest risk to the outstanding universal value of the World Heritage Area and its integrity."
Great Barrier Reef Marine Park Authority chief scientist Dr David Wachenfeld said everything possible should be done to create recovery windows.
"Gradual sea temperature increase and extremes, such as marine heat waves, are the most immediate threats to the reef," he said.
"Global action on climate change is critical."
The report said the window of opportunity to improve the Great Barrier Reef's long-term future was now, and strong and effective management was needed.
Environment Minister Sussan Ley said it was "unsurprising" the condition had deteriorated.
She said steps were already being taken to address the challenges, including the launch of a $6 million "Reef Resilience" vessel.
"This is an outlook we can change and are committed to changing," she said.
"It might take time to see these strategies translate into tangible outcomes, as in the case of humpback whale and southern green turtle populations, which continue to increase."
Ms Ley said the reef was the "best managed reef in the world" and reiterated the government's $1.2 billion funding commitment.
"We are taking the action that we're required to do under our Paris [climate change] agreements," she said.
She pointed to the various interventions being undertaken into water quality, sustainable fishing, and controlling the crown-of-thorns starfish while commending Indigenous land managers and farmers who were working to prevent sediment run-off into the reef.
"You only have to visit this part of Australia to see how much local people care for and love the reef," she said.
Ms Ley said another bleaching event soon would see the reef deteriorate further.
Coral bleaching and cyclones caused significant harm
Sea temperature extremes caused successive mass bleaching events in 2016 and 2017, which led to unprecedented and widespread coral loss and flow on effects to fish and invertebrate communities.
"Mitigating threats like climate change and poor water quality, coupled with resilience-based management, are essential to boosting Reef health so it can recover," said Dr Wachenfeld.
Researchers also noted that targets set for improvements in water quality have not been met.
According to the report, 50 per cent of the reef has been exposed to destructive waves from six tropical cyclones since 2014.
As an example, six reefs were surveyed following Cyclone Debbie in 2017.
They showed an average of 70 per cent loss of coral cover at two metres, and 64 per cent loss at depths of five metres.
In some areas, the loss was as high as 98 percent.
Impacts on tourism and World Heritage listing
The report said while the reef's value as a World Heritage Area remained "intact", its integrity is now "challenged and deteriorating".
"Human-induced climate change is challenging the integrity of the World Heritage Area, its size is becoming a less effective buffer against broadscale impacts," the report said.
A condensed version of the report will be provided to the United Nations in December, so it can determine if the reef's health has improved enough since 2014 in order to retain its Cultural Heritage status.
The Federal Government said 64,000 Australians depend on the $6.4 billion reef economy.
The research notes major changes to the condition of the ecosystem will have social and economic implications for regional communities, because commercial marine tourism and fishing depend heavily on a functioning, resilient ecosystem.
"As reef waters continue to heat, coral reefs will become less diverse than a decade ago, and the fishes seen while snorkelling and caught while fishing, will also change," the report said.
"Reef-dependent users need to prepare for this change."
GBRMPA will work with management partners, researchers, Traditional Owners and reef users such as tourism operators, fishers and local communities to communicate the report's findings.
Despite the poor outlook, GBRMPA chief executive Josh Thomas said the reef remained "beautiful and healthy" in large areas.
Reduction of 'pollutant loads' has been too slow
Poor water quality continues to affect many inshore areas of the reef.
The report found reduction of pollutant loads had been slow, reflecting modest improvements in agricultural land management practices.
The Federal and Queensland Governments have also released the Reef Report Card for 2017-2018.
It showed that while improvements have been made to land management practices, more work was urgently needed.
Governments have set a target to have 90 percent of affected grazing and sugarcane land covered by best-practice management systems by 2025.
However, both industries have scored poorly overall, with just 35.8 percent of grazing land and 9.8 percent of sugar regions meeting that target.
Ms Ley said farmers were doing their part.
"Under our actions around water quality, we have reduced sediment run-off into the reef by 5400 tonnes," she said.
"If you take the Burdekin catchment that provides most of the sediment, we're seeing a reduction of 47 percent.
"It's always important to work with the farmers; they're at the front line and they're absolutely our best asset when it comes to land management around the reef."
Queensland Canegrowers chief executive Dan Galligan said farmers had been working for decades to have both a profitable farm and a sustainable future.
"I think farmers across the state are taking responsibility where they can, and they've got to do their bit on their farms and that's what we're seeing," he said.
"The Marine Park Authority's actually recognised that things are changing in terms of water quality as a result of best-practice adoption.
They point to the fact that all that investment by farmers is a waste of time unless governments come together on a clear policy on climate change," he said.
A director of the Australian Marine Conservation Society, Imogen Zethoven, said the reports were concerning.
"Pollution running into the reef's waters from farming and coastal development continues to be a key threat, and the report is clear on this," she said.
"The Queensland Government has a bill in Parliament to help reduce land-based run-off. It needs to be passed and implemented as soon as possible. Cleaner water gives the reef the resilience it needs."
Another serious threat to the Great Barrier Reef is from the coral-eating Crown-of-Thornes Starfish (CoT), which can thrive on sediment run-off.
The reef is still experiencing an outbreak of the starfish, which began back in 2010 and continues to be graded as "very-poor".
The pests are difficult to manage and, coupled with coral bleaching, have led to a decline in coral cover.
Their impact is so severe that even if corals are not affected by any other disturbances, outbreaks can take at least 10 years to recover from.
In years to come, that recovery is expected to be further slowed by other stresses, including from climate change.