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The Great Barrier Reef, the largest living ecosystem on Earth, is facing an existential threat, scientists warn, as ocean temperatures reach their highest levels in 400 years.

A new study by Australian researchers shows that this natural wonder will not survive for future generations if global warming is not stopped.

Sea surface temperatures in the waters surrounding the Great Barrier Reef reached their highest levels in more than 400 years this year, according to a study published in Nature found on thursday.

“The Reef is in danger and if we do not change course, our generation will likely witness the demise of one of Earth’s greatest natural wonders, the Great Barrier Reef,” Benjamin Henley, lead author of the study, said at a news conference on Tuesday.

“The world is losing one of its icons,” said Mr Henley, who is also a lecturer at the University of Melbourne and an honorary fellow at the University of Wollongong. “I think it’s an absolute tragedy. It’s hard to understand how something like this could happen in our lifetime. So it’s very, very sad.”

Sea temperatures around the GBR have been steadily rising since the 1900s due to human activities such as the burning of coal, oil and gas, which have increased the emission of dangerous greenhouse gases after centuries of stable conditions.

From 1960 to 2024, the study authors observed an average annual warming of 0.12 °C (0.22 °F) per decade (January to March).

The research shows that the ‘unprecedented’ heat on the sea surface around the natural wonder is increasingly leading to mass bleaching events that are putting it at risk.

Since 2016, the reef has experienced five summers of mass coral bleaching, when temperatures rose so high that corals began to lose their color. This was because the algae that provide the corals with nutrients and color were rejected by the corals due to heat stress.

The research shows that these bleaching events occurred during five of the six warmest years in the last four centuries.

Co-author Helen McGregor said she was “extremely concerned” for the reef and described the temperature rises as “unprecedented”.

“These are corals that have been alive for 400 years and these are the hottest temperatures they have ever experienced. These are the Redwood trees of the reef,” she told AFP news agency.

The findings show that the Great Barrier Reef is approaching a tipping point from which it may not recover, and urgent action is needed to limit global temperature rise to a maximum of 1.5 degrees Celsius.

To analyze past temperature data, for which no data were available, the group of scientists drilled into coral and analyzed the samples, similar to counting tree rings. This allowed them to measure summer ocean temperatures going back to 1618.

The reef is home to a huge variety of natural life, with 600 species of coral and 1,625 species of fish alone. It is also a major tourism boon for Australia, contributing around $4.2 billion to the country’s economy each year.

But new findings are fueling debate over whether the reef should be classified as endangered. Australia is trying to keep it off the list so it doesn’t harm the tourism industry that contributes A$6.4 billion (£3.32 billion) to the economy each year.

The world is on track to see a temperature increase of 2-3 degrees by the end of the century. In fact, the past 12 months have already seen global temperatures rise 1.5C above pre-industrial levels, and also the warmest on record.

Under the Paris Agreement, the world is trying to keep global warming from exceeding 1.5C or 2C. But for corals, even a 2C increase could wipe out 99 percent of reefs.