Third Great Barrier Reef bleaching event

Cheryl Goodenough
Aerial surveys have revealed a third bleaching event on the Great Barrier Reef

The Great Barrier Reef has suffered another mass bleaching, experts have warned.

Scientist Terry Hughes says evidence of the third mass coral bleaching in five years is coming from an extensive aerial survey over hundreds of individual reefs.

It follows similar bleaching events in 2016 and 2017.

Professor Hughes says the bleaching has ranged from extreme in some parts of the Great Barrier Reef to low levels near Cairns and the Whitsundays.

He is currently doing aerial surveys of 1000 reefs to assess the full impact of coral bleaching.

Describing some bleaching as "awful", Prof Hughes wrote on social media the reefs north of Townsville have extreme levels of bleaching, typically affecting more than 80 per cent of corals.

Great Barrier Reef Legacy director Dr Dean Miller says he recently returned from Lizard Island where he documented the bleaching and experienced the impact of the marine heatwave first hand.

He warns the reef is struggling to cope with climate change.

"I saw coral bleaching both at the surface and as deep as 16 metres," Dr Miller said.

"The real question is how long can corals, and the ecosystem, hang on before we reach the point of no return?"

He said the bleaching was extensive, but fortunately tourism hotspots around Cairns and Port Douglas have been spared this year.

Climate Council chief executive Amanda McKenzie says Australia's immediate attention needs to be on the coronavirus, but even during this terrible time the threat of climate change must not be forgotten.

"The longer we delay meaningful climate action, the more devastating the consequences will be," she said.

Greenpeace Australia Pacific acting program director Kate Smolski called on the government to include measures to reduce greenhouse gas emissions in future economic stimulus announcements.

"Coal-driven climate change is threatening our beautiful reef, and the many communities and tourism workers who depend on a healthy reef for their livelihoods which are already at risk from the coronavirus outbreak," Ms Smolski said.