Coral reefs are at a tipping point after surging global temperatures

A recent rise in ocean temperatures has caused widespread bleaching and death of warm-water corals around the world, officially triggering the first climate tipping point for one of Earth’s ecosystems, scientists said.

The collapse of one of the world’s most diverse and fragile ecosystems poses a “risk to human health and safety” that governments are not prepared for, warns Melanie McField of Healthy Reefs for Healthy People, a conservation program in Florida run by the US Smithsonian Institution.

Warm-water coral reefs are home to up to a third of all known marine biodiversity and provide food, coastal protection and a source of income for a billion people worldwide. Reef services contribute $9.9 trillion in goods and services globally each year.

However, corals are very sensitive to changes in water temperature. Record global temperatures recorded since 2023 have pushed ocean heat levels to new heights, triggering a mass bleaching event that has affected more than 80% of all corals on the planet. Bleaching occurs when corals expel algae living in their tissues in response to high water temperatures, causing them to turn white. This makes corals vulnerable to disease, and prolonged bleaching can kill them completely by depriving them of their main food source.

The latest bleaching event was an “order of magnitude different” than anything scientists have observed before, McField says. “We are at the tipping point,” she confirms. This threshold is generally defined as a critical threshold which, if exceeded, could lead to dramatic and probably irreversible changes in the climate system.

McField is one of the authors of the chapter on corals in the Global Tipping Points Report 2025, released today. The report, the first update since 2023, is compiled by 160 scientists from around the world and coordinated by the University of Exeter in the UK and campaign group WWF. It warns that warm-water corals are the first land system to pass its tipping point and are now in the grip of an “unprecedented crisis”.

Central academic estimates suggest that the thermal limit for warm-water corals is reached when global atmospheric temperatures reach 1.2°C above pre-industrial levels, with an upper threshold of 1.5°C. In 2024, global average temperatures exceeded 1.5°C above pre-industrial levels for the first time in human history, an event that pushed the world’s coral reefs beyond the limits of their endurance, according to Tim Lenton of the University of Exeter, who led the report.

“We took a sample of a 1.5°C world and we saw the consequences,” he told reporters at a press briefing ahead of the report’s release. “The majority of coral reefs are at risk of significant decline. [or bleaching] and switch to an alternative algae-dominated and algae-covered state.

The best hope for saving the planet’s warm-water corals from near-complete extinction now lies in reducing global average temperatures to 1.2°C above pre-industrial levels as soon as possible, he says. Whether or not such an ambitious target – which goes well beyond the requirements of the 1.5°C temperature target – is achievable is another question, Lenton believes.

Terry Hughes, of James Cook University in Australia, warns that there are now “almost no unbleached reefs anywhere in the world.” But the situation can still be alleviated. “We can control where coral reefs will end up in the coming decades if global greenhouse gas emissions are quickly reduced,” he says.

Often what climate tipping point might be triggered is highly uncertain, but researchers warn that widespread decline of the Amazon rainforest, melting of polar ice caps, and collapse of the crucial AMOC ocean current could all occur at warming levels below 2°C.

But people can also trigger “positive tipping points” to mitigate risk, Lenton points out, pointing to the exponential growth of renewable energy over the past decade and the rapid adoption of electric vehicles. Rapid adoption of cleaner technologies could help reduce emissions on the scale needed to keep warming below 2°C, the report notes.

In a statement, Lenton said urgent action was needed from world leaders at the upcoming COP30 summit in Brazil to accelerate emissions reductions across the global economy and minimize the time global temperatures rise above 1.5°C. “We are rapidly approaching several tipping points in the Earth system that could transform our world, with devastating consequences for people and nature. This demands immediate and unprecedented action from COP30 leaders and policymakers around the world,” he said.