Nearly All Shallow Coral Reefs Face High Risk of Collapse by 2075, Review Finds

Almost every warm-water coral reef on Earth faces an extremely high risk of collapse within about 50 years, according to the first global assessment of coral reef ecosystems under the Red List of Ecosystems kept by the International Union for Conservation of Nature, which advises the United Nations on conservation.

The assessment, released Thursday, examined 127 tropical and subtropical reef regions covering about 188,000 square kilometers of reef. Once projected ocean warming was included, 96 percent were classified as critically endangered, the highest threat category, which means an extremely high risk of collapse before 2075. That list includes the largest and richest reef systems, among them Australia’s Great Barrier Reef, the Coral Triangle of Southeast Asia and the western Pacific, the Mesoamerican Barrier Reef and the reefs of the Red Sea.

Scientists consider a reef collapsed when the hard corals that build it nearly disappear and algae, rubble and sponges take over, leaving a far poorer habitat. Reefs support about a quarter of all known marine species and provide food, coastal protection and tourism income for hundreds of millions of people.

Heat is the main driver. Marine heat waves cause corals to expel the algae that give them color and nutrients, a process called bleaching that can kill them or leave them vulnerable to disease. The assessment assumed a middle-of-the-road emissions path used by the Intergovernmental Panel on Climate Change, which projects about 2.7 degrees Celsius of warming by the end of the century compared with preindustrial times. According to The Guardian, it did not fully account for the fourth global mass bleaching event, which ran from early 2023 into 2025 and was the most widespread on record.

Other pressures compound the damage. Overfishing of species such as parrotfish and grouper, which keep algae in check and balance reef food webs, threatens about 63 percent of reef ecosystems, the IUCN said, alongside coastal development, pollution, storms and outbreaks of coral-eating starfish.

The researchers stressed that the outcome is not fixed. Judged only on what has happened over the past 50 years, without future climate projections, 24 percent of reef ecosystems would be critically endangered rather than 96 percent. Some regions, including parts of East Asia and the northern Red Sea, have shown unusual resilience or heat tolerance. The western Galápagos reefs are already classed as collapsed, and four regions lacked enough data to assess.

The assessment’s scientific lead, Mishal Gudka, who the IUCN says is a research fellow at the University of Melbourne and research director at CORDIO East Africa, called the findings alarming but not hopeless and described them as a wake-up call. Grethel Aguilar, the IUCN’s director general, said reefs can still recover if countries cut emissions sharply, strengthen protection and restoration, and invest in coastal communities.

In Australia, all 17 reef regions were rated critically endangered once warming was included. The study’s authors argued that local measures such as cleaner coastal waters and sustainable fishing can buy time, but that cutting greenhouse gas emissions remains the deciding factor.