Global heating has pushed the world's coral reefs into a fourth planet-wide mass bleaching event, which US government scientists say is on track to become the most extensive on record. The National Oceanic and Atmospheric Administration's Coral Reef Watch confirmed that 54% of ocean waters containing coral reefs have experienced heat stress high enough to cause bleaching.
A global bleaching event is declared when at least 12% of corals in each of the main ocean basins—Pacific, Atlantic, and Indian—experience bleaching-level heat stress within a 12-month period, along with confirmed reports of bleaching. The current event began in early 2023 and has affected reefs across the Americas, Florida, the Caribbean, Brazil, the south Pacific, the Middle East, and parts of the Indian Ocean.
Coral Reef Watch also confirmed that Australia's Great Barrier Reef experienced its most widespread heat stress event on record in 2024, with 80% of the reef subjected to bleaching-level heat stress—the highest extent ever recorded, surpassing the previous high of 60% in 2017. The reef is now suffering its fifth mass bleaching in eight years.
Dr Derek Manzello, director of Coral Reef Watch, said the percentage of reef areas experiencing bleaching-level heat stress has been increasing by roughly 1% per week, and the current event is likely to surpass the previous most widespread event soon. He noted that global heating combined with a global El Niño has pushed up sea surface temperatures, and predictions made decades ago about the fate of corals are now coming to pass.
Coral reefs cover less than 1% of ocean area but provide habitat to a quarter of all marine species, support food and tourism income for millions, and protect coastlines. However, they are among the most vulnerable ecosystems to global heating. Prolonged and severe bleaching can kill corals, and even if they recover, they may struggle to reproduce and become more susceptible to disease.
Scientists have called for urgent action to reduce fossil fuel investments and address climate change. Dr Roger Beeden, chief scientist at the Australian government's Great Barrier Reef Marine Park Authority, emphasised the need for global action, stating that the prognosis for coral reefs is poor without significant emissions reductions.
