The world’s coral reef ecosystems almost all face a high risk of collapse in the next 50 years mostly due to warming oceans and heat waves, according to a global assessment released Thursday.

The International Union for Conservation of Nature’s assessment, announced on the sidelines of a U.N. biodiversity conference in Albania, found that 96% of shallow-water reef systems are already critically endangered and could disappear by 2075.

Most of the world’s famous reef systems — including 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 — are all critically endangered, the highest level of threat.

“The risk of coral reef collapse is escalating, but this must be a wake-up call rather than a cause for despair,” said Mishal Gudka, the scientific lead of the global IUCN Red List of Coral Reef Ecosystems assessment, the first of its kind.

“Coral reefs have shown a remarkable ability to bounce back from devastating bleaching events,” he said. “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 is the latest dose of bad news for coral reefs, which are critical sources for seafood and tourism and often serve as buffers from coastal erosion and storms. Sometimes dubbed “rainforests of the sea,” they have some of the world’s richest biodiversity. They support a quarter of marine species as well as coastal communities and businesses.

When a reef collapses, hard corals disappear and are replaced by algae, rubble and sponges. As a result, the reef no longer supports a diverse ecosystem that can include everything from tiny invertebrates to reef fish like grouper.

“Coral reefs are one of the clearest vital signs of the ocean’s health,” Grethel Aguilar, the IUCN Director General, said in a statement.

The assessment, spanning 127 tropical and subtropical ecoregions, and encompassing 72,726 square miles (188,362 square kilometers) of coral reefs globally, called climate change the “single most consistent threat driving coral reef decline worldwide.”

A week ago, another study in the journal Nature by the IUCN found that nearly 44% of reef-building coral species face an elevated risk of extinction due to climate change. A year ago, a survey found that harmful bleaching of the world’s coral has grown to include 84% of the ocean’s reefs — the most intense of its kind in recorded history.

2024 was Earth’s hottest year on record, and much of that is going into oceans. The average annual sea surface temperature of oceans away from the poles was a record 20.87 degrees Celsius (69.57 degrees Fahrenheit).

Beyond combatting rising global emissions, experts said efforts to reduce pollution, overfishing and coastal development can help reefs survive.

“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,” Aguilar said.

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