El Niño could spark wider coral bleaching this summer

NOAA warns that El Niño arriving in the next few months could trigger another major coral bleaching event this summer—potentially the fifth global event on record—after the last one ended just months ago.

For many coral reefs, the warning isn’t abstract anymore. It’s seasonal. This week, the U.S. National Oceanic and Atmospheric Administration warned that El Niño—expected to arrive in the next few months—could set off another mass coral bleaching event, just a year after the last one concluded.

If it happens as NOAA expects, it would be the fifth global bleaching incident in recorded history. NOAA’s updated coral bleaching outlook. shared Tuesday. forecasts that reefs face a high risk of losing their color this summer across much of the northern Pacific Ocean. including Hawaii. It also warns that reefs around Florida and the Caribbean may be hit.

Coral reefs don’t just look beautiful underwater; they support marine life and provide habitats for approximately one-fourth of all marine species. When ocean temperatures run hotter than corals can tolerate, reefs can deteriorate—stripping pigments and turning corals white. Visible bleaching has occurred often in recent decades, and many scientists tie the pattern to climate change.

Last October, researchers at the University of Exeter declared coral reefs the first environmental system on Earth to pass a climate “tipping point,” after years of repeated degradation.

NOAA’s Coral Reef Watch program, which produced the outlook, also points to a hard reality for monitoring these events. Derek Manzello. who coordinates the program. said in a statement that tracking mass bleaching is challenging because ongoing heat stress means these events are more common now than ever before. Then comes the part that raises alarm: the onset of El Niño. linked with warmer ocean temperatures. suggests the next episode may be arriving soon.

“We are now in the era where reefs will bleach on a near-annual basis, which means defining when global events begin and end is becoming increasingly difficult,” Manzello said. “The plan moving forward is to rely on field bleaching observations to determine if and when global events are happening.”

The last global bleaching event offers both a baseline and a clock. Research suggests it impacted 84% of the world’s reefs and ended halfway through 2025. If El Niño emerges as anticipated this summer, NOAA said coral bleaching could return in a big way between June and September.

Even then, timing won’t be simple. Scientists are fairly certain El Niño will arrive before the fall season begins. but they are still determining when it will happen exactly and how strong it will be. NOAA said stronger El Niño is more likely to prompt global coral bleaching. noting that global bleaching events have coincided with every strong El Niño since 1998.

Underlying conditions are also stacking the odds against reefs. Heat stress has become more severe and widespread, and sea surface temperatures are currently higher than they were during the first mass bleaching event almost three decades ago.

And yet, there’s an additional strand to this story—one that prevents the warning from being only grim. NOAA said scientists have found coral can be resilient. During the record-breaking bleaching event that occurred between 2024 and 2025, there were some reefs that resisted bleaching despite high ocean temperatures.

Jennifer Koss, director of NOAA’s reef conservation program, said the agency is studying “multiple aspects of heat tolerance in corals.” She added, “This will help us better understand resilience in corals and improve coral restoration strategies and techniques across the nation.”

The pieces now fit together in a way that’s impossible to ignore: warmer seas are arriving. bleaching is becoming more frequent. and NOAA’s forecast points toward another likely surge—this time starting between June and September—just as scientists are still trying to decide where the last global event truly ended.

El Niño NOAA coral bleaching Coral Reef Watch Hawaii reefs Florida reefs Caribbean reefs marine ecosystems heat stress ocean warming reef resilience climate tipping point University of Exeter heat tolerance coral restoration