Coral reefs around the world, struggling as climate change drives more frequent and more intense marine heat waves, are running out of time for recovery, according to a sweeping new report on the state of the world’s corals published on Monday.
The comprehensive global assessment builds on decades of research and coral monitoring, and highlights the devastating effects of warming on one of Earth’s most delicate and diverse ecosystems.
It found that the world’s coral reefs had declined by 9.5 percent in the period from 2020 to 2024, compared with 1980 to 2009. The largest single-year coral decline on record, which affected 87 percent of reefs worldwide, occurred in 2024.
But perhaps the most alarming finding is that reefs, which protect coastlines from storms and support at least a quarter of marine life at some point in their life cycles, now have a much narrower window for recovery.
Historically, global coral bleaching events have happened roughly once per decade. But since 2010, they’ve occurred every four to six years, according to the report.
Bleaching occurs when corals become so stressed that they lose the symbiotic algae they need to survive. Bleached corals can recover, but they need time to do so. If the water surrounding them is too hot for too long, they die.
The findings are “dire and serious,” said Manuel Gonzalez-Rivero, a researcher at the Australian Institute of Marine Science and the report’s lead author. Corals, he said, are no longer experiencing the natural ebb and flow of stress and recovery.
“Coral reefs take quite a long time to recover,” he said. “We’re talking about decades to actually regain back what they lost.”
The report, issued by the Global Coral Reef Monitoring Network, a worldwide organization of scientists and conservationists, comes as the world’s oceans warm to record levels, absorbing heat trapped in the atmosphere by greenhouse gases. Global average sea surface temperature last week reached a record 21.1 degrees Celsius, or about 70 Fahrenheit, breaking a record set in 2024, according to the Copernicus Climate Change Service, the European Union’s climate monitoring organization.
Some scientists say the state of coral reefs worldwide might actually be worse than the report suggests.
The full effect of the last and most intense global bleaching event, which began in 2023 and concluded in 2025, was not captured in the findings, which are based on data collected through 2024, said Carlos Duarte, a marine scientist who directs the Coral Research and Development Accelerator Platform, a global initiative focused on saving reefs.
He pointed to reefs in Western Australia that bleached for the first time last year, recent “major mortality” among Red Sea corals with little evidence of recovery, and reefs in the Caribbean that have lost about 90 percent of their genetic diversity.
This year’s brewing El Niño is “very likely” to cause yet another global bleaching event next year, Dr. Duarte said. Long term, he predicted, along with the Intergovernmental Panel on Climate Change, that the planet will lose 70 percent to 90 percent of its coral cover if long-term global warming reaches 1.5 degrees Celsius, and up to 99 percent if average global temperatures climb two degrees Celsius above preindustrial levels.
“The situation is far more disturbing than the report portrays,” said Dr. Duarte, who was not involved in the assessment.
Terry Hughes, a former director of coral reef studies at James Cook University in Australia, and who also was not involved in the Monday report, cautioned that coral cover measurements did not take into consideration underlying reef biodiversity.
“Coral cover could stay the same or even increase while biodiversity tanks,” he said. “So, the more complicated message is that the mix of coral species is changing globally, and the more vulnerable ones have been winnowed out for several decades.”
Some corals, for example, recover quickly but are more sensitive to heat. “It’s kind of like replacing a forest with grass,” Dr. Hughes said. “It comes roaring back quickly, but it’s flammable” and more susceptible to the next heat wave.
Local solutions, including reducing water pollution and protecting coastal ecosystems, can help coral reefs, but reducing planet-warming emissions is crucial, Dr. Hughes said.
“It really depends on how much more greenhouse gases go into the atmosphere and the amount of warming that causes,” he said.
