The assessment classifies about 24% of reef regions as critically endangered already. Under its emissions scenario, that rises to 96%, putting reef-supported food supplies, shoreline protection and tourism at risk.
An assessment coordinated by the International Union for Conservation of Nature (IUCN) projects an extremely high risk of ecosystem collapse before 2075 for 96% of shallow-water coral reef regions when expected global warming is included. The analysis covers 127 tropical and subtropical reef systems spanning 188,362 square kilometres and assumes about 2.7°C of warming above preindustrial temperatures by 2100.
IUCN is an international conservation group that advises the United Nations. Its assessment was released on 22 October, and scientific lead Mishal Gudka discussed coral risks at the UN’s COP17 biodiversity summit in Yerevan, Armenia.
The consequences extend beyond corals. A quarter of known marine species live in and around reefs, which provide food for hundreds of millions of people, protect shorelines and support tourism.
IUCN considers a reef ecosystem collapsed when it can no longer maintain itself because nearly all or all living reef-building corals have been lost. Hard corals disappear and are replaced by algae, rubble and sponges. The reef then no longer supports its diverse ecosystem, including small invertebrates and reef fish such as grouper.
The assessment therefore concerns the failure of whole ecosystems, rather than the extinction risk of individual coral species. Its risk classification does not mean collapse has already happened or is inevitable.
Overfishing, pollution, coastal development and warming have already driven reef declines over the past 50 years, the assessment found. Those declines were measured through losses of live coral and changes in fish populations. About 24% of reef regions across more than 80 countries are already classified as critically endangered; the 96% figure includes projected warming.
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| Basis of assessment | Share critically endangered |
|---|---|
| Existing degradation | About 24% |
| Including projected global warming | 96% |
The projection uses a middle-of-the-road pathway for greenhouse gas emissions, mainly from burning fossil fuels. The 96% figure describes the share of reef regions in a risk category; it is not a 96% probability that each reef will collapse.
Four reef regions lacked enough data for assessment, while western Galápagos reef ecosystems had already collapsed. IUCN said the share classed as critically endangered would likely be even higher if these gaps were accounted for.
The assessment also did not fully account for the fourth global mass bleaching event, from early 2023 to mid-2025. The US government’s Coral Reef Watch confirmed that it was the most widespread such event on record. Corals are heat-sensitive, and warming oceans increase the frequency and intensity of damaging bleaching events.
Scientists involved in the assessment describe the findings as an early warning, not an unavoidable outcome. They say reefs could survive with rapid reductions in fossil fuel use and strong local conservation action.
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.
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