First-of-its-kind IUCN reef assessment spans 127 ecoregions worldwide

Earlier studies documented coral extinction risk and widespread bleaching

Two studies on coral extinction and bleaching preceded the International Union for Conservation of Nature assessment. A week earlier, an IUCN study in the journal Nature found that nearly 44% of reef-building coral species face an elevated risk of extinction because of climate change. A year earlier, a survey found that harmful bleaching had grown to include 84% of the world’s reefs, the most intense of its kind in recorded history.

The assessment spans 127 tropical and subtropical ecoregions and encompasses 72,726 square miles (188,362 square kilometers) of coral reefs globally. It is the first assessment of its kind. IUCN released it Thursday and announced the findings on the sidelines of a U.N. biodiversity conference in Albania.

The assessment found that almost all coral reef ecosystems face a high risk of collapse in the next 50 years, mostly because of warming oceans and heat waves. It called climate change the “single most consistent threat driving coral reef decline worldwide.”

The assessment also said some 96% of shallow-water reef systems are already critically endangered and could disappear by 2075. It rated the Great Barrier Reef in Australia, the Coral Triangle in the Western Pacific Ocean and Southeast Asia, the Mesoamerican Barrier Reef System and the Red Sea coral reefs as critically endangered, the highest level of threat.

Coral reefs are critical sources for seafood and tourism and often serve as buffers from coastal erosion and storms. Sometimes dubbed the “rainforests of the sea,” they have some of the world’s richest biodiversity, support a quarter of marine species and also support coastal communities and businesses. IUCN director general Grethel Aguilar said in a statement, “Coral reefs are one of the clearest vital signs of the ocean’s health.”

When a reef collapses, hard corals disappear and are replaced by algae, rubble and sponges. The resulting reef no longer supports a diverse ecosystem that can include everything from tiny invertebrates to reef fish such as grouper.

Mishal Gudka, the scientific lead of the global IUCN Red List of Coral Reef Ecosystems assessment, said, “The risk of coral reef collapse is escalating, but this must be a wake-up call rather than a cause for despair.” He also said, “Coral reefs have shown a remarkable ability to bounce back from devastating bleaching events.” Gudka added: “Pockets of surviving, resilient coral reefs can still remain in the future, so we must do everything within our reach to set them up for success.”

The assessment came after 2024 was Earth’s hottest year on record, with much of the heat going into oceans. The average annual sea surface temperature of oceans away from the poles reached a record 69.57 degrees Fahrenheit (20.87 degrees Celsius).

Experts said that, beyond combating rising global emissions, efforts to reduce pollution, overfishing and coastal development can help reefs survive. Aguilar said: “We know what is needed: ambitious emissions reductions, stronger protection and restoration efforts, and sustained investment in resilient coastal ecosystems and the communities that depend on them.”

Andrew Baker, director of the Coral Reef Futures Lab at the University of Miami, commented after reviewing the assessment. He said stopping global warming and pollution “isn’t the only way to save corals.” “It means finding new ways to restore corals using emerging technology and innovative approaches,” he said, “that can throw a lifeline to struggling reefs and buy us critically needed time to make these transitions.”