The Intergovernmental Panel on Climate Change has made dire forecasts for the world's largest coral reef system ahead of an expected visit by UNESCO to help determine if it should be listed as a World Heritage site in danger.
The IPCC report bluntly says the Great Barrier Reef is in "crisis" and at very high risk of crossing a critical threshold where further warming might cause irreversible damage.
It also notes the reef's limited scope for adaption and warns of the potential for a dramatic escalation in the frequency of bleaching events like the one in 2016, which affected more than 90 per cent of the reef.
Under a high emissions scenario modelled in the report, such events could occur twice each decade from 2035, and annually after 2044.
Scientists have long warned the reef won't survive that, given it takes about a decade for a decent recovery of the fastest growing corals, and longer for slow-growing species.
The IPCC report said that if bleaching continues, Australia stands to lose an estimated 10,000 jobs and $A1 billion in revenue every year from tourism alone.
"Increased heat exposure also affects the abundance and distribution of associated fish, invertebrates and algae," it said.
Cyclone intensity will also increase, putting coral reefs further at risk.
The Australian Marine Conservation Society says the world stands to lose an asset of outstanding global significance without a rapid reduction in emissions this decade.
"We know the problem, we know the solution," says the group's reef campaign manager Lissa Schindler.
"Australia must rapidly phase out its relationship with coal and gas and embrace a renewable future."
UNESCO's Reef Monitoring Mission is expected to visit soon to review how the federal and Queensland governments are managing the reef.
UNESCO will then provide a draft decision to the World Heritage Committee about whether a World Heritage in Danger listing is warranted.
Last year, the World Heritage Committee told the federal government accelerated action, at all possible levels, was needed to address climate change threats to the reef.
"The Morrison government is yet to increase their climate ambition to what is needed for coral reefs to survive into the future," Dr Schindler says.
"With a 2030 emissions reduction target that remains at 26 to 28 per cent, and a 2050 net zero target that relies on technology that hasn't yet been invented, it is hard to see how UNESCO would not recommend the reef be listed (as in danger)."
The Morrison government has responded to the IPCC report by saying Australia has reduced emissions faster than many comparable countries, and pointing to $4 billion in joint federal and state funding for reef adaptation and resilience.
"This is the best managed reef in the world and we have invested a further $1 billion in its protection," a spokesperson for federal Environment Minister Sussan Ley said on Tuesday.
"We are addressing water quality, coral regeneration, predator eradication and fishing in ways that are strengthening the reef, while at the same time working domestically and internationally to address emissions.
"We are optimistic about the future of the reef, the communities and 64,000 jobs which depend on it."
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