El Niño Threatens Coral Reefs This Summer

The potential for another mass coral bleaching event looms as El Niño is expected to arrive in the next few months. This would mark the fifth global incident of its kind, occurring shortly after the previous one ended. NOAA's updated outlook indicates a high risk for reefs across much of the northern Pacific Ocean, Hawaii, Florida, and the Caribbean to lose their vibrant colors during the summer.

Coral reefs serve as essential underwater ecosystems, providing habitats for about 25% of all marine species. Excessive heat stress can cause these delicate environments to deteriorate and turn white. Scientists have observed that bleaching events are becoming more frequent, with some declaring coral reefs as the first environmental system to pass a climate tipping point due to repeated degradation.

Derek Manzello, coordinator for NOAA's Coral Reef Watch program, noted that ongoing heat stress makes bleaching events more common. The onset of El Niño, which is linked to warmer ocean temperatures, suggests a new event could be imminent. He stated that reefs are now experiencing bleaching on a near-annual basis, complicating the definition of global event timelines.

Research indicates that the previous global bleaching event, which affected 84% of the world's reefs, concluded in mid-2025. If El Niño emerges as anticipated, coral bleaching could surge between June and September. While scientists are confident El Niño will arrive before fall, its exact timing and intensity are still being determined, with stronger El Niños historically correlating with global bleaching events since 1998.

Despite the documented impacts of warming oceans, corals exhibit resilience. Some reefs resisted bleaching during the record-breaking event of 2024-2025, even under high ocean temperatures. NOAA is actively studying various aspects of heat tolerance in corals to enhance restoration strategies and techniques nationwide.