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Coral bleaching on the southern Great Barrier Reef.Credit:Grumpy Turtle Designs/ Australian Marine Conservation Society

The results are contained in the Australian Institute of Marine Science reef snapshot released on Wednesday.

“This is one of the most extensive bleaching events the reef has experienced in AIMS’ nearly 40 years of monitoring,” said Dr David Wachenfeld,research director at the institute.

“It’s the first bleaching event where we’ve had extreme bleaching in the northern,central and southern Great Barrier Reef.”

Marine heatwaves are becoming more severe and frequent,and science agencies list climate change as the greatest threat to the survival of coral reefs.

A global coral bleaching event was declared on Tuesday by the International Coral Reef Initiative. Coral reefs in 53 places have bleached since the start of last year,including in Florida,the Caribbean,the Eastern Tropical Pacific,the South Pacific,the Red Sea,the Persian Gulf,and the Gulf of Aden.

Mass coral bleaching events have occurred on the Great Barrier Reef in 1998,2002,2016,2017,2020,2022 and now 2024.

Coral bleaching occurs when organisms are under severe stress due to abnormally high water temperatures. Recovery is possible if sea surface temperatures return to normal quickly enough.

Bleaching causes corals to expel the algae living in their tissues and turn white. Scientists say global warming is the major factor driving more frequent bleaching.

Wachenfeld said it was too early to say how much coral would die as a result of the current bleaching event. Underwater surveys are being conducted to assess the extent of coral deaths and to determine to what depth corals have been affected.

“What worries me is that we will end up with a bleaching event where there’s a high level of mortality in the northern,central and southern regions of the reef,” he said.

Australia’s climate has warmed by an average of 1.47 degrees over the past century,according to the Bureau of Meteorology. A report by the Australian Academy of Science said that if the world warmed by 2 degrees,only 1 per cent of corals would survive.

The Caribbean has lost 80 per cent of its coral reefs,and environmental groups WWF and the Australian Marine Conservation Society have warned that Australia could face comparable damage without dramatic action to curb climate change.

“We’re calling on the prime minister to commit to a federal emissions reduction target of at least 90 per cent below 2005 levels by 2035,stop approving new fossil fuel projects,and support the worldwide push for a global treaty to phase out all fossil fuels,” WWF Australia head of oceans Richard Leck said.

The Queensland Labor government recently committed to a more ambitious climate target to cut emissions by 75 per cent by 2035.

However,the federal Labor government’s target to cut national emissions by 43 per cent by 2030 and reach net zero by 2050 is consistent withinternational efforts that would lead to 2 degrees or more of warming.

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