World’s fourth mass coral bleaching event, fastest and widest on record, likely ended in 2025

The fourth global coral bleaching event may have concluded in the mid-2025, scientists have said.

Researchers from the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch stated that after analysing satellite data and bleaching observations, the record-breaking event that was confirmed on April 15, 2024 concluded, causing 84 per cent bleaching-level heat stress.

As many as 83 countries and territories were impacted in all three coral reef housing ocean basins — Pacific, Atlantic and Indian Oceans.

Following the severe bleaching in Western Australia in early 2025, global heat stress has been in decline and there have been only isolated reports of coral bleaching.

The western Australia bleaching event likely bookended the fourth global event, the statement from NOAA said.
“We needed to confirm that no widespread, large-scale bleaching was reported anywhere during the austral summer which ran from December 2025 through February 2026, before we were confident the event had ended,” said Derek Manzello, Coordinator of NOAA’s Coral Reef Watch in the statement.

“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. The plan moving forward is to rely on field bleaching observations to determine if and when global events are happening,” he added.

The Global Tipping Points Report 2025 noted that earth reached its first catastrophic tipping point - that is widespread bleaching and death of coral reefs. 

The report stated that warm-water coral reefs, or shallow coral reefs in tropical and sub-tropical regions, are crossing their thermal tipping point and undergoing unprecedented die-off that threatens the livelihoods of almost one billion people who directly  and indirectly depend on reefs for food, income and coastal protection.

El Niño risks ahead

NOAA said that the expected emergence of El Nino in the coming months will result in an increase in ocean temperatures that could potentially resume the widespread coral bleaching.

It predicted that according to NOAA’s four-month coral bleaching outlook, the corals will be at a high risk across the north Pacific Ocean (including Hawai’i), Florida and the Caribbean during upcoming summer. 

Since 1998, global coral bleaching events have coincided with every strong El Niño event, with heat stress becoming more widespread and severe with each successive event. The first and second global coral bleaching events occurred in 1998 and 2010, respectively, followed by the third global coral bleaching event that spanned three years, from 2014-2017, the statement said. 

It noted that despite the massive scale of this fourth event, not all coral reef areas bleached even when exposed to high ocean temperatures. Scientists are looking into these locations to understand what factors may have contributed to their ability to resist bleaching, they added.


“NOAA and its partners are studying multiple aspects of heat tolerance in corals,” said Jennifer Koss, director of NOAA’s Coral Reef Conservation Programme. “This will help us better understand resilience in corals and improve coral restoration strategies and techniques across the nation.”



Even with the end of the fourth global event, sea surface temperatures are still higher than 25-30 years ago when the first global coral bleaching event occurred. 

The Global Tipping Points Report 2025 warned that the world has entered a dangerous “new reality” as global heating, driven by greenhouse gas emissions, nears the critical 1.5°C threshold.

“Thermal stress is now pervasive on our nation’s coral reefs,” said Manzello. “Frequent, regular monitoring is more vital now than ever before, as it is the only way to understand the biological and physical factors associated with bleaching resilience from the organism to ecosystem level,” he added.