Scientists warn Great Barrier Reef faces high bleaching risk

Scientists warned that Australia's Great Barrier Reef is at very high risk of extreme and widespread bleaching and possible ecosystem collapse linked to this year's El Nino weather phenomenon.

The reef stretches 2,300 kilometres, nearly 1,430 miles, along the coast of Queensland state and is a major tourism draw for Australia. It is often described as the world's largest living structure.

This month, the reef avoided being listed as endangered, although the United Nations had reported "utmost concern" about mass coral bleaching and the impact of climate change.

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 Nino" was a significant concern. He said it was possible that the next major disturbance could lead to localised species extinctions and widespread ecosystem collapse.

Pratchett also said there was a very high likelihood of very severe, large-scale mass bleaching on the Great Barrier Reef.

This year's El Nino is expected to break records for overall strength as it warms surface temperatures in the central and eastern equatorial Pacific Ocean, bringing worldwide changes in winds, pressure and rainfall patterns.

UNESCO has monitored the reef annually since 2021, when it warned the reef was at risk of being placed on the list of World Heritage items "in danger".

Hard coral cover across the reef declined substantially in 2024-2025. Above-average water temperatures caused the reef's sixth mass coral bleaching event since 2016. Extreme weather, land-based run-off, coastal development and predation by the Crown of Thorns starfish were also putting pressure on the reef.

Ove Hoegh-Guldberg, a marine studies professor at the University of Queensland, said insufficient government action had threatened the future of coral reefs worldwide. He warned that the threat to reefs was very serious and called for action.