Half of the Great Barrier Reef has been hit by high to very high bleaching, the new aerial surveys found, with and 10 per cent classed as extreme bleaching – when more than 90 per cent of corals are distressed.

Aerial surveys are conducted by sight from planes at 500 feet, giving the visibility of corals down to about five metres below the sea surface.

The more bleached corals, the higher the risk of deaths. But bleaching is not always fatal and corals can recover if the water cools down quickly enough.

Aerial surveys cannot determine the death rate. Underwater surveys are underway now to determine mortality from the current bleaching event.

WWF Australia head of oceans Richard Leck said the survey results indicated the bleaching event hit all three regions of the reef – north, central and south – which would be unprecented in scale.

“Previous bleaching events have crossed into two of the reef regions and that’s usually been the north and the central regions,” Leck said.

Australia’s climate has already 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 if the world warmed by 2 degrees, only 1 per cent of corals would survive.

The Albanese government’s target to cut national emissions by 43 per cent by 2030 and reach net zero by 2050 is consistent with international efforts that would lead to 2 degrees or more of warming.

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

UNESCO has said Australia must demonstrate that the Great Barrier Reef should not be listed as “in danger” – and risk losing its World Hertiage status – at a meeting in July.

Australia has argued it is making sufficient gains on climate action and environmental actions. The government’s special envoy for the Great Barrier Reef, Nita Green, recently went to UNESCO headquarters in Paris with marine park authority chief executive Josh Thomas to make this argument.

“As special envoy for the Great Barrier Reef I work with all parties who are committed to the health of the Reef, that includes meeting with UNESCO on the ongoing health, protection and management of our precious World Heritage site.”

Greens oceans spokesperson Peter Whish-Wilson accused the federal government of attempting to “deliberately deceiving the world” about the severity of climate change impacts on the reef.

“It’s time for no more spin, deceit and distractions. The Greens are calling for full transparency of any recent lobbying of UNESCO by the Albanese government,” Whish-Wilson said.

Federal Environment Minister Tanya Plibersek said the government had boosted Australia’s climate target since its 2023 election win and was committed to improving reef health.

“We know the biggest threat to coral reefs worldwide is climate change. The Great Barrier Reef is no exception,” Plibersek said.

We’ve legislated to reach net zero, with a 43 per cent emissions reduction target by 2030 and committed to reaching 82 per cent renewable energy by 2030. And we’re investing a record $1.2 billion in the Reef including to ensure we have the best science on reef adaptation and resilience.”

Green’s office has been contacted for comment.

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