The Fourth Global Bleaching Event Is Over. It Touched 84% of the World's Reefs.

On 2 June 2026, NOAA announced that the fourth global coral bleaching event — the largest on record — likely concluded in mid-2025.

From early 2023 to mid-2025, bleaching-level heat stress hit 84% of the world's coral reef area, across all three ocean basins that contain reefs: Pacific, Atlantic, Indian. Mass bleaching was documented in at least 83 countries and territories.

Eighty-four percent. That is not a regional event. That is very nearly all of them.

What "ended" means here, precisely

This is the part worth slowing down for, because the headline invites exactly the wrong conclusion.

"Ended" means heat stress stopped arriving. It does not mean the coral recovered.

A bleached coral is not a dead coral. It has expelled the symbiotic algae that live in its tissue, provide most of its food, and give it its colour. Bleached coral is starving, not deceased. If the water cools soon enough, it can take the algae back and survive. If not, it dies.

The end of an event is the end of the stressor. What the reefs look like on the other side is a separate question, measured separately, over years. Some reefs will have come through. Some are gone. In parts of the Pacific coast near Mexico, mortality reached as high as 93%.

So: the fire is out. Nobody has finished counting the house.

How NOAA decided it was over

The methodology is a good example of a conservative call.

Severe bleaching in Western Australia in early 2025 appears to have bookended the event. But NOAA didn't declare it over then. They waited through the austral summer of December 2025 to February 2026 — the Southern Hemisphere's hottest window, when any resurgence would show up — and confirmed no widespread bleaching was reported anywhere.

Only then did they call it.

That is roughly a year of waiting to be sure. It is the opposite of a press release chasing a news cycle, and it is why this figure can be trusted more than most.

The sentence in the announcement that should worry you

Derek Manzello, who coordinates NOAA's Coral Reef Watch, said something in the announcement more consequential than the headline:

"We are now in the era where reefs will bleach on a near-annual basis."

Read that again, because it quietly dismantles the category the headline uses.

A "global bleaching event" is a meaningful concept only if bleaching is episodic — if there are normal years and event years. If reefs bleach nearly every year, then "the event ended" stops describing anything real. You cannot have an exception without a rule.

NOAA is explicit that this is now a measurement problem: defining when global events begin and end is becoming increasingly difficult, and the plan is to shift toward field bleaching observations rather than the current framing.

The scientists are saying the scoreboard may no longer fit the game. That is a bigger statement than "the event is over."

The pattern, four events deep

Since 1998, every global coral bleaching event has coincided with a strong El Niño — and heat stress has become more widespread and more severe with each successive event.

Note the durations: one year, one year, three years, roughly two and a half. And note the gaps: twelve years, four years, six years.

The events are not obviously getting more frequent in a clean line. They are getting bigger. And the baseline underneath them has moved — sea surface temperatures remain higher than they were 25 to 30 years ago when the first event occurred. Each El Niño now starts from a warmer floor.

What happens next is already forecast

NOAA expects El Niño to emerge within months.

Their four-month bleaching outlook shows high risk across much of the north Pacific including Hawai'i, plus Florida and the Caribbean, later this summer.

Given that every global event since 1998 has coincided with a strong El Niño, that forecast is not a vague worry. It is a specific expectation with a map attached.

The fourth event ended nine months ago in NOAA's reckoning. The conditions associated with the start of every previous one are forecast to arrive within months.

The part that isn't bleak

Not every reef bleached, even where the water got hot enough that it should have.

Those refuges are now the subject of active research: NOAA and partners are studying heat tolerance in corals to understand what made some places resist. If the mechanism is genetic, it can inform restoration. If it's local — shading, currents, upwelling — it can inform where to put protection.

That is the difference between mourning reefs and doing something. Some corals already know how to survive this. Finding out how they do it is a tractable scientific problem, and it is being worked on.

Why this is on AEDO1

Coral reefs occupy well under 1% of the ocean floor and support roughly a quarter of all marine species. They also break waves before those waves reach coastlines where people live.

The headline is that an event ended. The story is a NOAA scientist saying the word "event" may not survive contact with the next decade.