IUCN projects 96% of shallow-water reefs face high collapse risk before 2075

Scientists say reefs could survive rapid fossil-fuel cuts and strong local conservation

An assessment coordinated by the International Union for Conservation of Nature (IUCN) finds that 96% of the world’s shallow-water coral reefs face a high risk of ecosystem collapse before 2075 once the expected impacts of global heating are added. The assessment analyzed the current status and future threat levels of 127 coral reef regions, and about 24% of the planet’s reefs across more than 80 countries were already critically endangered before the projection was applied. IUCN, an international group that advises the United Nations, coordinated the work.

Coral reefs are known as the rainforests of the sea. A quarter of all known marine species are found in and around them, and they support hundreds of millions of people with food, protect shorelines and sustain tourism. Overfishing, pollution, coastal development and global heating have already caused declines in reef ecosystems over the past 50 years, the assessment said. Those declines were measured through the loss of live coral and changes in fish populations.

The assessment assumed greenhouse gas emissions, mainly from burning fossil fuels, would follow a “middle-of-the-road” pathway, causing about 2.7°C of global heating by the end of the century compared with temperatures before the Industrial Revolution. The assessment also found that current climate policies and targets adopted by countries around the world are likely to cause about 2.6°C of global heating. IUCN said the share of reef eco-regions considered critically endangered would likely be even higher.

Four reef regions did not have enough data for the assessment, and the coral reefs of the western Galápagos had already collapsed, IUCN said.

The assessment found a high risk of ecosystem collapse in 96% of shallow-water reef regions after expected global heating impacts were added. IUCN’s “critically endangered” classification meant an “extremely high risk” of ecosystem collapse before 2075. The group considers a coral reef ecosystem to have collapsed if the reef could not maintain itself because of a near or complete loss of living reef-building corals.

Before expected climate impacts were included, four of Australia’s 17 reef regions were critically endangered, five were endangered and five more were classified as vulnerable. Once expected climate impacts were accounted for, all 17 regions, including the Great Barrier Reef, were critically endangered. Dr Ben Fitzpatrick of the University of Western Australia Oceans Institute led the Australian assessment.

The assessment did not fully account for the impacts of the fourth global mass bleaching event, which ran from early 2023 to mid-2025. The US government’s Coral Reef Watch confirmed that it was the most widespread global mass bleaching event on record.

The global event was bookended by the worst mass bleaching event on record for reefs in Western Australia, where a heatwave killed corals across 1,500 kilometres (930 miles). A photograph by Brooke Pyke shows extensive coral bleaching at Ningaloo Reef in Western Australia in February 2025.

Marine heatwaves can cause corals to separate from the symbiotic algae that provides them with colour and nutrients. While bleaching is not always deadly, it can weaken corals and make them more susceptible to disease.

The scientists who produced the assessment said the prognosis was dire, but the findings should serve as a “wake-up call” because reefs could survive with rapid cuts to fossil fuel use and strong conservation action at local levels. A caption accompanying a photograph of Papa Bay, Hawaii, by Lindsey Kramer for the Hawaii Wildlife Fund and IUCN describes scientists’ view of the risk findings as a “wake-up call” to rapidly cut the use of fossil fuels.

Dr Mishal Gudka, research director at CORDIO (Coral Reef Degradation in the Indian Ocean) East Africa and the assessment’s scientific lead, said, “The risk is real and very concerning.” He added, “We stand to lose one of the most valuable ecosystems we have – the impacts of which will affect millions of people around the world.” Gudka described the results as a “wake-up call” and as “alarming, but certainly not hopeless.” He said, “They should be seen as a call to action – an early warning sign before the worst outcomes eventuate.”

Dr Grethel Aguilar, the director general of the IUCN, said, “It is not too late to give coral reefs a chance to recover, but it requires decisive action to tackle climate change and halt further ocean warming.” She also 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.”

Fitzpatrick said that even after accounting for the ability of some corals to adapt to warmer water, the rising heat “overwhelmed everything.” He said, “Reefs are like Picasso paintings underwater. They have all these wonderful inhabitants in their millions. You can spend a lifetime trying to understand how all these weird critters go about their daily lives. To think we might lose that is devastating. There’s one message. We have to stop burning fossil fuels.”