Manuel González Rivero has spent years counting coral. He is a reef expert at the Australian Institute of Marine Science and lead author of a new global report on reef health. His main finding is about time. Reefs once had decades to recover after major bleaching events, he says, but today they are lucky to get five or six years. With a very strong El Niño now building in the Pacific, even that may be generous.
How strong is this El Niño?
Strong, and still growing. NOAA’s Climate Prediction Center said on 8 October that El Niño continues to strengthen, with a strong-to-very strong event likely through January–March 2027. It gave an 83% chance that the October–December index would reach at least +2.5°C, a level that would exceed every El Niño in its record back to 1950. UN Secretary-General António Guterres has said a warming climate is “supersizing” El Niño.
Why does El Niño matter so much to coral?
El Niño is a natural pattern in which surface waters warm across the central and eastern equatorial Pacific, lifting global ocean temperatures and amplifying marine heatwaves. Corals live close to their heat limit. When the water gets too warm they expel the algae they rely on for food, which leaves them open to starvation and death. That is bleaching.
The link is well documented. Since 1998, every strong El Niño has been associated with a Global Coral Bleaching Event. Derek Manzello, who coordinates NOAA’s Coral Reef Watch, told Mongabay-India that there have been four such events, and each has hit more reefs than the one before.
What changed about the starting line?
The baseline moved. Manzello points out that global mean sea surface temperature from 2019 to 2023 equalled the maximum recorded in 1998, the year of the first global bleaching event. He adds that ocean temperatures during recent La Niña conditions, the cool phase, exceed those of El Niño events three to four decades ago. An El Niño today adds its heat to an ocean that is already hot.
How much coral has already been lost?
The report is from the Global Coral Reef Monitoring Network. It compiled 21.1 million observations from 36,886 reef sites in 124 countries and territories, with more than 40 years of data. It found that the fourth global bleaching event (2023–2025) drove an 8.9% relative drop in hard coral between 2023 and 2024 alone, the largest single-year decline on record.
Recovery has happened, but slowly. Julia Baum, a coral ecologist at the University of Victoria who was not involved in the report, says recovery after the third global event was minimal and that she would not call 6% a rebound.
Can reefs bounce back at all?
The report says they can, given time. Reefs keep the ability to regain hard coral when disturbances are reduced and enough recovery time is available. The Maldives is the example held up. A 1997–98 event of similar strength killed 90 per cent of shallow-water coral there, yet the recovery was convincing enough for the report to cite it as proof of rebound.
Time is the problem. González Rivero says that for many reefs hit by the 2024 marine heatwaves, this year’s El Niño leaves little more than a year to recover before the next blow, creating a “staircase of decline.” UNEP, drawing on the same network’s findings, likened reefs to an overmatched boxer taking repeated blows.
Is every reef affected the same way?
No. Mongabay India reports that Indian reefs respond very differently from region to region, which points to local conditions and the need for sustained monitoring through the 2026–27 El Niño. Local pressures matter too. The report’s authors say poor water quality, overfishing and coastal development leave reefs less able to withstand heatwaves.
Scientists agree that cutting emissions is the main lever. Baum says steep, immediate cuts in greenhouse gases are essential to avoid losing most reefs this century. The IPCC’s assessment is that 70–90% of today’s warm-water reefs will disappear even if warming is held to 1.5°C.
Whether the 2026–27 El Niño becomes a fifth global bleaching event is not yet known. Baum calls it likely. How many reefs will have recovered enough to survive it has not been measured.
