WASHINGTON -- Ocean temperatures in the Great Barrier Reef hit their highest level in 400 years over the past decade, according to researchers who warned that the reef likely won’t survive if planetary warming isn’t stopped.

Between 2016 and 2024, the Great Barrier Reef, a global treasure known for its vast coral reef system and rich biodiversity, endured multiple episodes of severe coral bleaching. This occurs when water temperatures rise excessively and the coral polyps expel the algae that provide them with nourishment and vibrant colors, sometimes leading to their demise. Recent aerial surveys, conducted earlier this year, examined over 300 reefs within the system located off the northeastern coast of Australia. These surveys revealed that bleaching affected shallow water areas across two-thirds of the reef, as reported by the Great Barrier Reef Marine Park Authority.

Scientists from Melbourne University and other Australian universities, in a study published Wednesday in the journal Nature, were able to compare current ocean temperatures to historical ones by using coral skeleton samples from the Coral Sea. These samples enabled them to reconstruct sea surface temperature data from 1618 to 1995. They then combined this data with sea surface temperature records from 1900 to 2024.

Temperatures remained relatively constant before 1900, followed by a continuous increase from January to March between 1960 and 2024. Notably, during five coral bleaching events in the last ten years – in 2016, 2017, 2020, 2022, and 2024 – January and March temperatures were significantly higher than any recorded since 1618. The researchers employed climate models to determine that the warming trend after 1900 is attributable to human-induced climate change. Only 2004 exhibited temperatures comparable to those during the mass bleaching years of the past decade.

“The coral reef is in peril and unless we change our current trajectory, our generation will likely see the end of one of nature's grand marvels,” said Benjamin Henley, the lead author of the study and a lecturer of sustainable urban management at the University of Melbourne. “If you combine all the evidence ... extreme heat is happening too frequently for these corals to adapt and evolve effectively.”

Coral reefs are vital for global seafood production and tourism. Experts have consistently warned that further coral loss is a probable consequence of future warming as the planet nears the 1.5 degrees Celsius (2.7 degrees Fahrenheit) limit, which nations committed to strive for in the 2015 Paris climate accord.

Even if the Paris Agreement's target for limiting global warming is met, an objective that scientists believe Earth is nearly certain to exceed, the study's authors stated that 70% to 90% of coral reefs worldwide could face danger. Consequently, future coral reefs would likely exhibit reduced diversity in coral species — a trend that has already begun as the oceans have become warmer.

Coral reefs have been undergoing transformations over the past 25 years due to bleaching events like those highlighted in the study, stated Michael McPhaden, a senior climate scientist at the National Oceanic and Atmospheric Administration who was not involved in the research. However, even the most resilient coral may soon be unable to withstand the increased temperatures anticipated under a warming climate with “the persistent rise in greenhouse gas levels in the atmosphere,” he stated.

The Great Barrier Reef is a vital economic asset for the area and provides protection from intense tropical storms.

As more heat-resistant coral replaces the less heat-resistant species in the vibrant underwater ecosystem, McPhaden expressed "serious concern" about the anticipated significant decline in the diversity of species and the shrinking size of the world's largest reef.

“It acts as an early warning signal for climate change,” McPhaden said.

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An error in the 2nd paragraph has been rectified. The aerial surveys were conducted by the Great Barrier Reef Marine Park Authority, not NASA as previously stated.

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