In 1998, unusually hot ocean temperatures stressed corals worldwide, causing them to expel the microalgae living within their tissues that normally nourish the tiny animals and give them color. Over the next year, more than 20 percent of the world’s reefs turned white during the first global coral bleaching event on record.
Fortunately, some of the affected reefs had time to recuperate as ocean temperatures cooled. More than a decade passed before the second global coral bleaching event began in 2010.
Since then, reefs have had roughly half that amount of time to recover between major bouts of heat stress as marine heat waves have become more frequent and intense, new research shows.
“Coral reefs once had decades to recover after major bleaching events. Today, they’re lucky to get five or six years,” Manuel González Rivero, a research scientist at the Australian Institute of Marine Science, said in a statement. He was lead editor of the Status of Coral Reefs of the World: 2025, the latest and most comprehensive report to date on the health of coral ecosystems.
The Global Coral Reef Monitoring Network, a group of scientists and research organizations that track coral reef health worldwide to guide conservation efforts, released the report last week. It found that the narrowing window for recovery has contributed to a significant decline in hard coral cover. This includes reef areas dominated by living stony corals that build the ecosystem’s complex three-dimensional structure.
Without sufficient hard coral, reefs lose the architecture that serves as habitat for fish and other marine life. That infrastructure also helps serve as a natural barrier for coastlines against waves and storm surge. Every year, at least 5 million people benefit from that protection, according to the latest assessment.
“The report is a critical reminder that coral reefs are the frontline of climate change,” Rachel Sapery James, who leads World Wildlife Fund’s Coral Reef Rescue Initiative and was not affiliated with the latest assessment, said in a message to Inside Climate News. “We need to pair local conservation action with much stronger global emissions reduction if coral reefs are to survive this century.”
Over the last 40 years, the report found that 10 percent of the world’s hard coral cover has been lost, primarily due to human-induced climate change. In some places, the decline has been far steeper, including the Caribbean, where more than 40 percent of hard coral cover has died due to compounding pressures, including heat stress and coral disease.
This scope of loss is concerning, but researchers are even more worried that corals no longer have ample time to recover, reproduce and rebuild reef structure before a major heat wave stresses them again, said Tadzio Bervoets, from Sint Maarten, who works as the Caribbean coral researcher for the Coral Restoration Consortium and the executive director of a marine conservation organization in Jamaica, the Alligator Head Foundation. He also contributed to the report.
Corals are slow-growing animals that can take decades to rebound from heat stress, but they are capable. In fact, the report shows that between 2017 and 2019, after the third global bleaching event, global hard coral cover increased by around 6 percent.
These days, they don’t even get that minimal reprieve.
For instance, the most recent and fourth global bleaching event, which began in 2023 and exposed nearly 85 percent of the world’s reefs to bleaching-level heat stress, ended just last year. Yet, reefs are already expected to experience another period of intense stress in the coming months.
In August, the daily global average sea surface temperature reached a record high of 70 degrees Fahrenheit, surpassing the previous record set in 2024, according to the Copernicus Climate Change Service. El Niño conditions intensified by climate change could warm the ocean temperatures even more. The National Oceanic and Atmospheric Administration has warned that corals may experience widespread bleaching as a result, especially in the North Pacific Ocean—which includes Hawaii—as well as in Florida and the Caribbean.
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Donate Now“This year’s El Niño likely means they’ll have had little more than a year to begin recovering before being hit again,” González Rivero said in his statement. “This is creating a staircase of decline that becomes harder to reverse with every bleaching event.”
Up to a billion people depend on coral reefs for food, livelihoods and cultural practices. Recreational exploration of reefs also supports a $36 billion tourism industry each year.
As reefs continue to suffer, “the systems that we know and the services that they provide are not going to be maintained,” González Rivero said in an interview.
Effectively conserving these invaluable ecosystems will require greater efforts to reduce both global greenhouse gas emissions as well as local threats like overfishing and pollution.
In the Caribbean, for example, Bervoets said, poor water quality caused by sewage, agricultural runoff, sedimentation and poorly regulated coastal construction projects continue to jeopardize reefs. These pressures can weaken corals and reduce their chances of surviving heat stress—if they don’t destroy the coral outright.
As these threats are being addressed, World Wildlife Fund’s James added, it is critical to invest in ongoing monitoring, coral restoration projects and protection of degraded reef habitats while engaging local and Indigenous peoples in the process.
“We need defence on all fronts,” she wrote in a message.
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Thank you,
Teresa Tomassoni
Oceans Correspondent
Teresa Tomassoni is an environmental journalist covering the intersections between oceans, climate change, coastal communities and wildlife for Inside Climate News. Her previous work has appeared in The Washington Post, NPR, NBC Latino and the Smithsonian American Indian Magazine. Teresa holds a master’s degree in Journalism from the Craig Newmark Graduate School of Journalism at CUNY. She is also a recipient of the Stone & Holt Weeks Social Justice Reporting Fellowship. She has taught journalism for Long Island University and the School of the New York Times. She is an avid scuba diver and spends much of her free time underwater.
