Australia’s Great Barrier Reef is at very high risk of extreme and widespread bleaching and “ecosystem collapse” linked to this year’s El Niño weather phenomenon, leading scientists have warned.

The Great Barrier Reef is one of the world’s largest living structures, stretching 2,300 kilometres along Queensland’s coast.

But, warming seas are increasing the frequency of coral bleaching events, while ocean acidification is hindering new coral growth.

Hard coral cover across the reef declined substantially in 2024-2025, with above-average water temperatures causing the reef’s sixth mass coral bleaching event since 2016.

The Great Barrier Reef avoided being listed as endangered this month, despite the United Nations reporting “utmost concern” about mass coral bleaching and the impact of climate change.

Scientists are now concerned that the looming El Niño could cause further detrimental damage to the reef. This year’s El Niño is expected to break records for its overall strength as it warms surface temperatures in the central and eastern equatorial Pacific Ocean, bringing worldwide changes in winds, pressure and rainfall patterns.

In the Great Barrier Reef this could mean the localised extinction of species, and potentially widespread ecosystem collapse.

Morgan Pratchett, a marine conservation ecologist at Queensland’s James Cook University, told the International Coral Reef Symposium in Auckland, New Zealand, that the “extreme El Niño” posed a significant concern.

“It’s a very high likelihood that we’ll see very high severity and large-scale mass bleaching on the Great Barrier Reef,” Pratchett said.

UNESCO has been monitoring the reef annually since 2021, when it warned it was at risk of being placed on the list of World Heritage sites “in danger.”

Extreme weather, land-based runoff, coastal development and predation by the crown-of-thorns starfish were also placing the reef under pressure.

Ove Hoegh-Guldberg, a professor of marine studies at the University of Queensland, said global governments’ inaction is posing a serious threat to the ecosystem. 

He warned that the damage done to these ecosystems should act as a warning system and prompt wider – and urgent – systemic change.

“This could be the precursor to the loss of humans,” he said, “If you were on a big boat, like the Titanic, and someone comes up to you and says the boat’s going down, you bloody well get on those lifeboats and start acting and do stuff.”

“We’re not doing that. The ship is starting to sink in a really massive way, and we’re not seeing it as what it is,” he added, “It is so serious.”

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