Atypical weather patterns cause coral bleaching on the Great Barrier Reef, Australia during the 2021-2022 La Niña.

Widespread coral bleaching was observed over the Great Barrier Reef, Australia, the world's largest coral reef during the 2021-2022 La Niña. This raised concerns that background global warming may have crossed a critical threshold causing thermal stress to corals during a climate state historically associated with increased cloud cover, rainfall and cooler summer water temperatures. Here we present an analysis of recent summer La Niña events focused on their synoptic meteorology and corresponding water temperatures over the Great Barrier Reef. Results show that the 2021-2022 summer La Niña caused accumulated coral heat stress to exceed previous La Niña conditions by 2.5 times. We find that weather patterns that favoured the build-up of heat in water overlying the Great Barrier Reef during the 2021-2022 summer were likely the result of repositioning of planetary scale atmospheric longwaves. This insight provides an additional means to predict potential future atmospheric conditions that increase the risk of extremely high water temperatures and coral bleaching in the Great Barrier Reef.