▶ Watch Video: Ecologist warns sudden coral bleaching is “like pulling the plug on a TV”
The expected arrival of El Niño in the next few months could trigger another mass coral bleaching event, just a year after the last one’s conclusion, the National Oceanic and Atmospheric Administration warned this week.
This would mark the fifth global bleaching incident in recorded history if it comes to fruition, said NOAA, a U.S. federal agency that also conducts weather and climate research around the world. Its updated coral bleaching outlook, shared Tuesday, predicts that reefs are at a high risk of losing their colors this summer across much of the northern Pacific Ocean, including Hawaii. Reefs surrounding Florida and the Caribbean may face the same threats, the latest outlook said.
Coral reefs are vital underwater ecosystems that broadly support marine life and provide habitats for approximately one-fourth of all marine species. The undue stress of higher ocean temperatures can cause them to deteriorate, stripping them of their pigments and turning them white.
Visible bleaching has occurred often and at times infamously in recent decades, a pattern that many scientists attribute 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.
Brett Monroe Garner / Getty Images
Derek Manzello, who coordinates the Coral Reef Watch program that produced NOAA’s bleaching outlook, said in a statement that tracking mass bleaching events is challenging because ongoing heat stress means they are more common now than ever before. But the onset of El Niño, which is associated with warmer ocean temperatures, indicates the next one may be happening 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,” he said. “The plan moving forward is to rely on field bleaching observations to determine if and when global events are happening.”
Research suggests the last global bleaching event — which impacted 84% of the world’s reefs, breaking records — 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.
Scientists are fairly certain at this point that El Niño will arrive before the fall season begins, but they are still working to determine exactly when it will happen and how strong it will be. The stronger it is, the more likely it will prompt global coral bleaching, NOAA said, because global bleaching events have coincided with every strong El Niño since 1998.
Heat stress has also 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.
Although the consequences of warming oceans on reef health have been well-documented, scientists also found coral to be resilient. During the record-breaking bleaching event that ocurred between 2024 and 2025, there were some reefs that resisted bleaching despite high ocean temperatures, NOAA said.
Jennifer Koss, director of NOAA’s reef conservation program, said in a statement that the agency is studying “multiple aspects of heat tolerance in corals.”
“This will help us better understand resilience in corals and improve coral restoration strategies and techniques across the nation,” she said.