NOAA experts have determined that the fourth global coral bleaching event likely concluded in mid-2025 following unprecedented heat stress across the world’s coral reefs.

From 2014–2017, marine heatwaves caused global mass coral bleaching, where the corals lose their symbiotic algae. The authors find, this event exceeded the severity of all prior global bleaching events in recorded history, with approximately half the world’s reefs bleaching and 15% experiencing substantial mortality.

Benefits to society from coral reefs, including fisheries, tourism, coastal protection, pharmaceutical discovery and more, are estimated at about $9.8 trillion per year. For the first time, an interna...