The Great Barrier Reef has experienced five mass bleaching events since 1998

Coral bleaching occurs when ocean temperatures rise by just 1°C above the summer maximum for more than four weeks — the coral expels its symbiotic algae (zooxanthellae), turning white. Without the algae it cannot feed and dies. The Great Barrier Reef, the world's largest living structure at 2,300 kilometres, experienced its first mass bleaching in 1998; since then it has bleached in 2002, 2016, 2017, 2020, and 2022. The 2016 and 2017 back-to-back events killed an estimated 50% of the reef's shallow-water corals. Scientists have named ocean warming as the primary driver.

Source: Hughes et al., Nature (2017, 2018)