SYDNEY - Australia’s Great Barrier Reef faces the risk of near-annual coral bleaching with temperatures in surrounding waters found to have reached the highest in at least four centuries.
The Coral Sea has seen relentless extreme heat in recent years, with peaks this year and in 2017 and 2020 assessed to have been the warmest in at least four centuries, researchers from several Australian universities said in a study published Thursday.
Scientists warned the world's largest coral system, off the coast of Queensland, is under existential threat from more frequent bleaching events if oceans continue to warm at the current rate.
"In the absence of rapid, coordinated and ambitious global action to combat climate change, we will likely witness the demise of one of the earth's most spectacular natural wonders," said Benjamin Henley, a paleoclimate scientist at the University of Wollongong who was involved in the study.
To prevent this, countries must urgently ramp up action to meet commitments made under the Paris Agreement and make the switch from fossil fuels to renewable energy sources, he said in an interview.
A diver snorkels during an inspection of the reef's condition in an area called the 'Coral Gardens' located at Lady Elliot Island, north-east of the town of Bundaberg in Queensland, Australia, on June 11, 2015. (File photo: Reuters)
When ocean temperatures rise, the algae that corals rely on for food turn toxic and are expelled, causing corals to turn white and die — known as bleaching — unless the water cools.
To assess temperature changes in the Coral Sea, scientists combined existing records spanning the last 124 years with modelling that used coral samples to reconstruct conditions as far back as 1618.
Combined with ship and satellite data going back around a hundred years, the results show ocean temperatures that were stable for hundreds of years begin to rise from 1900 onwards as a result of human influence, the research concluded.
From 1960 to 2024, the study's authors observed an average annual warming for January to March of 0.12 degrees Celsius (0.22 degrees Fahrenheit) per decade.
The Great Barrier Reef, roughly the size of Japan, generates about A$6.4 billion (US$4.2 billion) from tourism, fishing and other industries, according to a 2017 Deloitte Access Economics analysis, and is listed by the United Nations (UN) as a world heritage site.
It has seen five mass bleaching events in the past decade. Earlier this year, surging ocean temperatures triggered the second global coral bleaching event in a decade, affecting coral reefs in every major ocean basin across 54 nations and territories including in Australia.
Since 2016, the reef has experienced five summers of mass coral bleaching, when large sections of the reef turn white due to heat stress, putting them at greater risk of death.
These summers were during five of the six warmest years in the last four centuries, the study showed.