On April 15, 2024, NOAA (in partnership with the International Coral Reef Initiative) confirmed the world is in the midst of its 4th global coral bleaching event. From 1 January 2023 to 30 September 2025, bleaching-level heat stress has impacted ~84.4% of the world’s coral reef area and mass coral bleaching has been documented in at least 83 countries and territories. The percentage has remained the same as of the latest update. The ongoing global coral bleaching event is the biggest to date. The previous record was during the 3rd global coral bleaching event, which occurred from 2014-2017, when 68.2% of the world's reef area experienced bleaching-level heat stress. The 1st and 2nd global coral bleaching events occurred in 1998 and 2010, respectively. NOAA CRW's 5km Bleaching Alert Area Maximum product, for the period January 1, 2023 - Septemebr 30, 2025. This map displays the maximum accumulated heat stress experienced by coral reefs around the world since January 1, 2023. The dark red/brown areas show the accumulated heat stress capable of causing reef-wide bleaching with mortality of heat-sensitive corals. The light brown (Alert Level 3), pink (Alert Level 4), and dark purple (Alert Level 5) areas on the map indicate locations where the magnitude of extreme heat stress exceeds the Bleaching Alert Level 2 threshold, and can lead to multi-species or near complete mortality on a coral reef. An animation of NOAA CRW's Daily 5km Bleaching Alert Area Maximum product, for the period January 1, 2023 - November 30, 2025. (For an animation covering the period of January 1, 2023 - September 30, 2025, click here.) As NOAA and its partners work to document the extent and severity of mass bleaching on coral reefs around the world, the GCBE4 also provides an opportunity for NOAA CRW to compare field data of coral bleaching and mortality with its