Global coral reefs face irreversible decline as bleaching frequency doubles, report warns

Global coral reefs are losing their ability to recover between marine heatwaves, with the time between bleaching events shrinking to as little as five or six years, according to a report published Monday by the Global Coral Reef Monitoring Network.

The assessment, the most comprehensive of its kind, drew on more than 21 million observations from 36,886 reef sites across 124 countries and territories, spanning over 40 years. It found that hard coral coverage— the proportion of reef surface covered by living coral—has declined by 9.5 percent compared with the 1980–2009 average, falling from just over 30 percent during 2009–2020 to 25.8 percent in 2024. Researchers attributed the drop primarily to climate-driven heat stress, which triggers bleaching when abnormally warm sea temperatures cause corals to expel the algae living in their tissues.

The report, titled *State of the World’s Coral Reefs: 2025*, was presented in Palau. It documented four major global bleaching events since 1998, each followed by significant hard coral losses: 6.5 percent in 1998–99, 9.9 percent in 2010–11, 6.6 percent in 2016–17, and 8.9 percent in 2023–24. Bleaching does not immediately kill corals, but prolonged heat stress can lead to death if temperatures do not drop in time for recovery.

Manuel González Rivero, lead author and a scientist at the Australian Institute of Marine Science, said the frequency of bleaching events has nearly doubled, leaving reefs with insufficient time to regenerate. “We had 40 years of coral cover around the world that had remained relatively unchanged until 2010,” he said. “Since 2010, there has been a very steep change.” The latest bleaching in 2023 was the most extensive on record, affecting 77 percent of the world’s coral reef areas, according to the report .

Coral reefs cover less than 0.2 percent of the ocean floor but support at least a quarter of all marine life, the report noted. Scientists warned that without longer recovery periods, the ecosystems risk irreversible decline. The GCRMN, a global network of researchers and conservationists, called for sharp reductions in greenhouse gas emissions and stronger measures against local stressors such as overfishing, poor water quality, and coastal development.

The current El Niño climate phenomenon may further shorten recovery windows for reefs hit by severe heatwaves in 2024, researchers added .