Great Barrier Reef in Australia | Water temperature at highest in 400 years, study reports

(Sydney) A record for several centuries: the water temperature of the famous Great Barrier Reef in Australia has been higher in the last 10 years than in 400 years, according to a scientific study published Wednesday.

Water temperatures had been rising every year since 1960, but were particularly high during recent coral bleaching events, according to the study published in the prestigious scientific journal Nature. A warming of the waters which is very probably the consequence of climate change caused by human action.

Study co-author Helen McGregor said she was “extremely concerned” about the “unprecedented” rises in water temperatures.

The Great Barrier Reef, which stretches 2,300 km along the coast of the state of Queensland (north-east Australia), is considered the largest living structure in the world. It is home to an extremely rich biodiversity, with more than 600 species of coral and 1,625 species of fish.

The phenomenon of coral dieback, which results in discoloration, is caused by an increase in water temperature which causes the expulsion of the symbiotic algae that give it its bright color. If the high temperatures persist, the coral turns white and dies.

Australian researchers studied surface temperatures in the Coral Sea using samples of ancient coral to reconstruct temperatures since 1618.

While temperatures were relatively stable before 1900, they found that the sea had warmed by an average of 0.12°C per year since 1960.

During the last massive bleaching events (2016, 2017, 2020, 2022 and 2024), temperatures were even higher.

Even if corals can recover, increasingly warm water temperatures combined with successive bleaching events are putting them under strain, warns Helen McGregor.

“These changes, from what we see so far, appear to be happening too quickly for corals to adapt, which really threatens the reef as we know it,” warns the climate researcher at the University of Wollongong (Australia).

Extreme damage

This year’s bleaching event, one of the most severe and widespread ever observed, left 81% of the reef with extreme damage, according to the latest government data.

Scientists will not be able to determine for several months how much of the reef is beyond repair.

“So far, we’re seeing the reef is resilient,” said Richard Leck, head of oceans at World Wildlife Fund Australia. “It’s recovered from previous coral bleaching events, but at some point the rubber band is going to snap.”

“Coral reefs are the first ecosystem on the planet to be threatened in their existence by climate change,” he warns.

“We have to hope that the world is not going to sit back and let this happen. But there is only a fraction of a second left until midnight,” Leck warns.

In June, UNESCO called on Australia to take “urgent” action to protect the Great Barrier Reef, including by adopting more ambitious climate targets.

The UN agency wants Canberra to submit an update by early 2025 on its efforts to protect and preserve the coral, but does not recommend placing the site on its list of world heritage in danger.

Australia has invested around $3.2 billion (€1.92 billion) to improve water quality, reduce the effects of climate change and protect endangered species.

But the country, one of the world’s largest exporters of gas and coal, has only recently set targets to become carbon neutral.