Water temperature at Australia's Great Barrier Reef reaches hottest in 400 years

Warming ocean waters have led to mass coral bleaching events in Australia's Great Barrier Reef (GBR) and are threatening the future of this UNESCO World Heritage Site. Now, researchers fundedin part by the U.S. National Science Foundationreport in the journal Naturethat seawater at the coral reef is at the highest temperature it's been in 400 years.

To make the determination, the scientists used core samples taken from the reef, reconstructed summer sea surface temperatures in the surrounding Coral Sea and modeled those temperatures with and without climate change.

"This study underscores the advantage of using climate archives, such as corals, to extend the record to better understand modern ocean climate variability," says Alan Wanamaker, a program director in the NSF Division of Ocean Sciences. "The research demonstrates the importance of NSF's support to study past climate conditions."

In the years 2024, 2020 and 2017, the Coral Sea reached its warmest in four centuries, with 2024 marking the highest water temperature.

"Without urgent intervention, the iconic GBR is at risk of experiencing temperatures conducive to near-annual coral bleaching," state the scientists in the study, "with negative consequences for biodiversity and ecosystem services. A continuation on the current trajectory would further threaten the ecological function and outstanding universal value of one of Earth's greatest natural wonders."