New 400-Year Record Shows Great Barrier Reef Faces Catastrophic Damage – State of the Planet

Australia’s Great Barrier Reef is under unprecedented pressure, with recent record-high sea-surface temperatures threatening to destroy its remarkable ecology, biodiversity and beauty, according to a new study. The study reconstructs 400 years of summer surface temperatures in the surrounding Coral Sea, providing new evidence that repeated recent coral-bleaching events are linked to increasingly warm summer temperatures―a result of human-caused climate change, the authors say. The study was just published in the journal Nature.

The Great Barrier Reef, encompassing some 133,000 square miles off Australia’s northwest coast, is the world’s largest reef system. It contains thousands of species of fish, molluscs, sponges, crustaceans and many other creatures. Hundreds of coral species comprise the base of the ecosystem, but the corals are stressed when water temperatures suddenly rise beyond normal levels in the austral summer. This causes them to expel the colorful symbiotic algae that inhabit their white skeletons, leading to so-called mass bleaching events. Bleaching does not kill corals outright, but it does make them more vulnerable to starvation and disease, especially if events happen frequently enough that algae populations have trouble recovering.

The research team combined sea-surface temperature reconstructions using geochemical data from coral cores previously collected from the region. They also analyzed climate-model simulations of sea-surface temperatures run with and without climate change. They found that six years over the past two decades were the warmest in the entire 400-year record. In order, starting with the warmest, these were 2024, 2017, 2020, 2016, 2004 and 2022. All the years except 2004 coincided with mass bleaching events. The study concluded that human-caused climate change is to blame.

The magnitude of the recent warming astounded the researchers. University of Melbourne lecturer Benjamin Henley, who led the study, said, “When I plotted the 2024 data point, I had to triple check my calculations. It was off the charts, far above the previous record high in 2017. Tragically, mass coral bleaching has occurred yet again this year.”

“At least over the past 400 years, the frequent bleaching going on now year to year seems unprecedented,” said study coauthor Braddock Linsley, a coral specialist at the Columbia Climate School’s Lamont-Doherty Earth Observatory. “It seems to be connected with what is going on with the global climate.”

Helen McGregor of the University of Wollongong, the second author of the study, said urgent action to stem climate change is needed to prevent devastation of the reef system. “There is no ‘if, but or maybe,’” she said. “The ocean temperatures during these bleaching events are unprecedented in the past four centuries.”

The authors say the research has implications for coral reefs throughout the world, highlighting the link between the long-term trajectory of extreme ocean temperatures and the health and biodiversity of marine ecosystems.

Adapted from a press release by the University of Wollongong.