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The Great Barrier Reef will continue to deteriorate as the impacts of global warming are "locked in", a report on its status has found.
And despite coral reefs doing better than expected, urgent action is required for the reef's long-term survival as a narrowing window to save it inches closed.
The Great Barrier Reef Outlook Report, tabled on Friday in the Senate, gives a long-term lens on what the reef can expect to look like based on the past five years.
"Future warming already locked into the climate system means that further degradation is inevitable," the report said.
"This is the sobering calculus of climate change."
The new report uses data from January 2019 to December 2023, meaning it does not encompass the 2023-24 summer bleaching events.
The Great Barrier Reef Marine Park Authority (GBRMPA) said urgent climate action to limit global warming to 1.5 degrees Celsius was critical, but the current state of affairs was "falling short".
"Every increment of additional global warming will further compromise the reef's unique biodiversity, with continuing consequences for cultural heritage, social and economic benefits, and the broader ecosystem services of the reef," it said.
"The window of opportunity to secure a positive future for the Great Barrier Reef is closing rapidly.
"Only the strongest and fastest possible actions to decrease global greenhouse gas emissions will reduce the risks and limit the impacts of climate change on the reef."
Climate change was the greatest threat to the World Heritage Area, GBRMPA chair Ian Poiner said in a letter to the Minister for Environment and Water Tanya Plibersek.
He urged "urgent national and global action" to create recovery windows for the reef in the face of cascading threats to its existence.
Coral in better shape than expected
Surprisingly, despite numerous mass coral bleaching events across the reef in the last eight years, the state of coral reefs has improved.
Relatively few coral reefs died in the 2020-2022 bleaching event and the general absence of cyclone damage meant coral was able to recuperate at a rate faster than expected.
The federal government has announced a further $192 million in funding for water quality programs for the reef. (Supplied: Great Barrier Reef Marine Park Authority/Jumbo Aerial Photography)
Outbreaks of crown-of-thorns starfish, a native marine invertebrate which feeds on coral and which has been a major source of coral loss, were minimal thanks to effective culling and control programs, GBRMPA chief scientist Roger Beeden said.
Coral across the reef is still classed as "highly vulnerable" alongside other indicators of the reef's health.
"Overall, the condition of habitats remains poor on a region-wide scale, in large part due to the ongoing vulnerability of coral reef habitats," the report said.
GBRMPA chief executive Josh Thomas said climate change posed the biggest threat to the reef's ecosystem.
"Global, national, and local action to reduce greenhouse gas emissions is vital," he said.
Marine species under pressure
A number of animal species across the reef recorded a drop in population, particularly marine turtles, sharks and rays and some bird populations.
The report said there was a long-term decline evident in dugong populations in the southern reef, but a stable population north of Cape Bedford, near Cooktown.
Poor water quality on the reef will be the focus of funding to reduce nutrient and pesticide run-off and improve the health of wetlands, announced on Friday by Ms Plibersek.
Hotspots across the reef's area will be eligible for $192 million in funding for programs that work towards improving water quality.
Ms Plibersek said Labor understood the responsibility of protecting and safeguarding the World Heritage Area, and pointed to the government's legislation of net zero emissions by 2043 and other funding commitments for the reef totalling $1.2 billion.
"The Great Barrier Reef is part of our national heritage," she said.
"We're funding projects that improve the reef's ability to recover after a bleaching event, like eradicating feral and invasive species and removing marine debris.
"We have a duty to safeguard and restore the reef, so future generations can also enjoy it."
Dugong populations in the south of the reef are in decline, the authority said in its five-year update. (Supplied: Violeta J Brosig)
UNESCO has flagged placing the Great Barrier Reef on a list of sites "in danger" multiple times, but held off doing so once more in July this year.
Instead, Australia must provide the committee in charge of the decision with a progress report in 2025 on actions that have improved the health of the reef.
A study published in Nature earlier this year found between January and March 2024 was the warmest sea surface temperature period for waters surrounding the reef in more than four centuries.