The Great Barrier Reef is being hit with a widespread and severe bleaching event, just three days before a United Nations delegation is due to arrive to assess the health of the world heritage area.
The Great Barrier Reef Marine Park Authority (GBRMPA) confirmed the bleaching is widespread in both the far north and the central sections of the reef, with the bleaching in the central parts rated as "severe".
Surveys are still underway to assess the full extent of the damage.
The last serious bleaching event on the reef occurred just two years ago.
The Reef Authority's chief scientist, David Wachenfeld, said the situation was "concerning".
"In the areas of central Great Barrier Reef where heat stress has been the worst over this summer, we are starting to see some coral mortality," Professor Wachenfeld said.
Widespread serious bleaching was not seen until 1998, but with soaring greenhouse gas emissions heating the globe, it appears to now be a common occurrence.
Mass bleaching was again seen in 2002, 2016, 2017 and 2020.
Professor Wachenfeld told the ABC the GBRMPA would not officially declare a "mass bleaching event" until they were able to examine all the data.
"There certainly is a risk that we are seeing a mass bleaching event," he said.
Bleaching occurs when the water is too warm, for too long. The coral expels the algae living inside it, leaving it colourless. The algae also provides the coral with most of its energy. If temperatures don't return to normal, the coral dies.
Reefs can recover from bleaching, but it takes years. If bleaching occurs regularly, the reef ecosystem can collapse.
Environmental groups have again called on the federal government to increase its ambitions for reductions in greenhouse gas emissions in line with a warming trajectory that is consistent with the reef surviving.
2022 a coral bleaching 'first', professor says
This bleaching is occurring in the midst of a La Niña weather pattern, which usually brings cooler temperatures, as well as cloud and rain, which protects the reef from bleaching.
"Corals on the Great Barrier Reef are not supposed to bleach in cooler La Niña summers," James Cook University's Professor Terry Hughes said on Twitter.
"2022 is a first, thanks to anthropogenic heating. It's been a mere 24 years since the first 1998 mass bleaching occurred during an El Niño heatwave."
Lissa Schindler from the Australian Marine Conservation Society agreed.
"It shows the consistent pressure our Reef is now under from global heating," Dr Schindler said.
"A healthy reef can recover from coral bleaching but it needs time. Regular marine heatwaves caused by the burning of coal and gas means it is not getting this time."
Richard Leck from World Wide Fund for Nature (WWF) Australia said the sixth significant bleaching event showed the reef was in grave danger.
"That's four times since 2016. The reef is now suffering widespread bleaching damage at the rate of more than once every two years," Mr Leck said.
A spokesperson for Environment Minister Sussan Ley said: "Any time we see bleaching it is a concern and it is why we are investing an additional $1 billion in the reef, to strengthen its resilience in the face of these challenges.
"This is the best-managed reef in the world and as a result of our collaborations with scientists, reef managers, traditional owners, farmers and local communities it is also the most closely monitored."
UN delegation visiting the reef soon
The official announcement from GBRMPA comes just days before the UN World Heritage Centre's monitoring mission arrives in Australia to assess whether the reef should be added to the list of World Heritage In Danger.
The monitoring mission, which arrives on Sunday, was established after Ms Ley complained that UNESCO's recommendation to add the reef to the in-danger list occurred without such a mission taking place.
Ms Ley's office has not confirmed whether the mission will be taken to see any of the bleaching, or whether they will only see unbleached coral.
When asked, a spokesperson said: "The mission will have access to all aspects of the reef it requires to complete its work."
Calls for Australia to step up on emissions reductions
When UNESCO last year recommended the Great Barrier Reef be put on the list of World Heritage In Danger, one of the key issues was Australia's weak emissions reductions targets.
It warned "accelerated action at all possible levels is required to address the threat from climate change in accordance with the Paris Agreement".
In the recommendation, UNESCO said it "strongly invites" Australia to take action on climate change that was consistent with protecting the Great Barrier Reef.
It also noted, specifically, that keeping warming at 1.5C above pre-industrial levels would significantly reduce the risks of climate change to the reef.
According to the Intergovernmental Panel on Climate Change, even if the world follows a low-emissions pathway, we are likely to see bleaching conditions on the reef every year by the middle of the century.
"We really need the strongest and fastest possible global action to reduce greenhouse gas emissions in order to secure a better future for the the Great Barrier Reef," Professor Wachenfeld said.
Richard Leck from WWF was an official observer to the World Heritage Committee when it made the decision not to immediately list the reef as in-danger.
"Coral bleaching is directly attributable to climate change caused by rising global emissions. Reducing Australia's domestic and exported emissions fast, this decade, is the main solution within our control," he said.
WWF-Australia commissioned an analysis by two leading climate scientists from the University of Melbourne, examining the gap between Australia's targets and a pathway consistent with stopping warming at 1.5C.
It found Australia's targets meant we would emit more than twice as much greenhouse gas as is possible for Australia to remain consistent with the 1.5C pathway.
"There is a clear gap between the emissions reduction consistent with limiting warming to 1.5C and Australia's emissions targets," said Professor Malte Meinshausen, one of the authors on the report.
