The Great Barrier Reef is threatened by the warmest sea in 400 years, according to study

Water temperatures around the spectacular marine ecosystem have increased annually since 1960, but were particularly high in connection with several recent coral bleaching events, according to the study, which was published in the journal Nature Wednesday.

The report says the increased temperature in the ocean is most likely due to man-made climate change. Co-author and climate scientist Helen McGregor at the University of Wollongong in Australia says she is “extremely concerned” about the reef and says the rise in temperature is unprecedented.

– These are corals that have lived for 400 years, and these are the hottest temperatures they have experienced. This is the reef’s answer to the mammoth trees on land, she tells AFP, referring to the giant sequoia, which grows wild in California.

Fragile and diverse ecosystem

The Great Barrier Reef is often referred to as the world’s largest living structure. It stretches over 2,300 kilometers along the north-east coast of Australia and is the basis of life for an enormous diversity of species, with over 600 types of coral and 1,625 species of fish.

Repeated cases of mass bleaching – where extreme heat drains the corals of nutrients and color – threaten the fragile ecosystem. Coral bleaching occurs when the temperature in the ocean rises by more than 1 degree.

Scientists have used samples from coral skeletons to reconstruct the surface temperature in the sea from 1618 to 1995. They have shown that temperatures were relatively stable before 1900, but that the sea has become 0.12 degrees warmer on average since 1960.

During the five cases of mass coral bleaching in 2016, 2017, 2020, 2022 and 2023, the temperature was significantly higher.

– Existential threat

Richard Leck, who leads World Wide Fund Australia’s work on the ocean, says the reef’s future is becoming increasingly vulnerable.

– At the moment we see that the reef is resilient. It has recovered from previous bleaching, but at some point the elastic breaks. Coral reefs are the first ecosystem on earth to face an existential threat as a result of climate change, says Leck.

– I think we must have hope that the world will not stand by and watch that happen. But we are a fraction of a second away from midnight, he tells AFP.