There is "irrefutable and indisputable" scientific evidence that the Great Barrier Reef is deteriorating due to climate change, UNESCO has said, as it pushed back against the Morrison government's fury over its move to declare the natural wonder endangered.
UNESCO oceans specialist Fanny Douvere has also rejected Australia's claims that it was denied due process or the target of a politically motivated attack, insisting its draft recommendation to list the reef "in danger" was based on an objective assessment of the best available science.
Dr Douvere's comments came as the federal government continues to cry foul over the UNESCO World Heritage Committee's draft ruling, with Prime Minister Scott Morrison on Wednesday morning lashing the decision-making process as "appalling".
Australia has now been backed up by 11 other nations, whose representatives to the UN body have co-signed a letter expressing their collective concern about the listing process.
Environment Minister Sussan Ley this week said the government had been "blindsided" by the decision, claiming Australian officials had been assured just a week ago that no such recommendation would be put forward.
She claimed the draft ruling from the China-led committee was politically motivated, while UNESCO's process was flawed because it had not inspected the reef in person.
Ms Ley said Australia had invested $3 billion in preserving the Great Barrier Reef, which she heralded as the best managed in the world.
The Morrison government fears an "in danger" listing could tarnish the reef's reputation as a global tourism destination. It has vowed to fight the decision ahead of the heritage committee's next meeting in July.
Speaking to The Canberra Times from France, Dr Douvere said Australia's response was "very understandable" given Australia's financial investment in conserving the Great Barrier Reef.
But Dr Douvere rejected the Morrison government's claims that it had been mistreated, insisting the decision was based not on politics but on scientific evidence.
"With three consecutive [coral] bleachings in less than five years the science has been irrefutable and indisputable that the reef does meet conditions for an "in danger" listing," she said.
The draft decision said climate change was to blame for the reef's mass bleaching events in 2016, 2017 and 2020 and called for "accelerated action at all levels" to address the threat of global warming.
Climate scientists and reef experts have warned Australia needs to set more ambitious emissions reduction targets in order to help protect the ocean jewel.
Dr Douvere said Australia could do more, including cutting emissions and increasing efforts to meet water quality targets.
But she said the draft listing should send a message to the entire international community about the threats of climate change. The science was clear, she said, that coral reefs could not survive if global average temperature rise exceeded 1.5 degrees.
"That is the duty of UNESCO ... to alert the international community on the reality of the reef," she said.
"This is an opportunity to unite, this is an opportunity to stand together, especially in the face of climate change."
Meanwhile, Mr Morrison used a radio interview on Wednesday morning to condemn UNESCO's actions.
"The UNESCO process has been appalling," he said.
"This process is not on. There's a proper way to do these things," he said.
"We invest, together with the Queensland government, some $3 billion on reef sciences, the best managed reef in the world.
"Sure, it's got challenges like sensitive environments all around the world, but Australia does it better than anywhere else, so we will be making that case."
Labor's environment spokeswoman Terri Butler said it wasn't helpful for her speculate on the possible political motives behind UNESCO's decision.
"[But] I think it's important for the government to explain exactly why they say the UNESCO decision was so unexpected. The government needs to be transparent, UNESCO needs to be transparent."
Ms Butler again called on the Morrison government to do everything it could to avoid the "in danger" listing, as she accused it of failing to heed repeated warnings about the reef's decline.