Climate Change & Coral Reef Futures

Coral bleaching occurs when sustained water temperatures exceed the thermal tolerance of coral-dinoflagellate symbioses, causing corals to expel their zooxanthellae and turn white. The frequency of mass bleaching events has increased fivefold since the 1980s, with back-to-back events in 2016–2017 killing half of the shallow-water corals on the Great Barrier Reef. Under a high-emissions scenario, models project that 99 percent of tropical reefs will experience annual severe bleaching by 2050. The window for preserving reef ecosystems is narrowing rapidly.