Coral reefs are at a tipping point after surging global temperatures

A notable increase in ocean temperatures has led to a significant incidence of bleaching and mortality among warm-water corals globally, marking the onset of the first climate tipping point for a vital ecosystem, according to scientists.

The disintegration of one of the planet’s most diverse ecosystems represents a “human health and security risk” that many governments are ill-equipped to address, warns Melanie McField from Healthy Reefs for Healthy People, an initiative in Florida supported by the US Smithsonian Institution.

Warm-water coral reefs sustain up to a third of all marine biodiversity and are crucial for food provision, coastal defenses, and providing livelihoods for nearly one billion individuals worldwide. The services provided by reefs are valued at up to 9.9 trillion dollars annually.

However, corals are extremely vulnerable to fluctuations in water temperatures. The unprecedented global temperatures recorded since 2023 have raised ocean heat levels to alarming highs, provoking a widespread bleaching event affecting over 80 percent of the world’s corals. This bleaching occurs when corals expel the algae from their tissues in response to elevated water temperatures, leaving them bleached and exposed to diseases, with prolonged bleaching potentially resulting in their complete demise due to starvation.

This latest bleaching event is characterized by a “far greater magnitude” than previous occurrences, according to McField. “We are witnessing a tipping point,” she emphasizes. Generally, this is recognized as a critical limit that, when breached, may induce dramatic and likely irreversible changes to the climate system.

McField contributed to the chapter on corals in the Global Tipping Points Report 2025, which has just been released. The report is the first revision since 2023 and is the result of collaboration among 160 scientists globally, coordinated by the University of Exeter and the WWF. This alarming report states that warm-water corals have crossed into their tipping point and are now in an “unprecedented crisis.”

Scholarly estimates indicate that warm-water corals reach their thermal limit when global atmospheric temperatures rise 1.2°C above pre-industrial levels, with an upper threshold at 1.5°C. In 2024, global averages surpassed 1.5°C above pre-industrial levels for the first time in recorded history, an occurrence that has caused coral reefs to exceed their tolerance, according to Tim Lenton from the University of Exeter, who spearheaded the report.

“We’ve sampled the world at 1.5°C, witnessing the implications,” he commented during a press briefing prior to the report’s release. “Most coral reefs are at risk of significant dieback [or bleaching] and moving towards a seaweed-dominated, algal-covered state.”

The most reliable chance to protect warm-water corals from near-total extinction now hinges on reducing global average temperatures to 1.2°C above pre-industrial benchmarks swiftly, states Lenton. Whether this ambitious objective—exceeding even the 1.5°C target—is attainable remains a critical discussion.

Terry Hughes from James Cook University in Australia cautions that there are “virtually no unbleached coral reefs left anywhere on earth.” However, remediation efforts are still feasible. “The fate of coral reefs in the coming decades depends on our actions, if we can significantly curtail global greenhouse gas emissions,” he advises.

While the timeline for triggering climate tipping points remains uncertain, researchers warn that the decline of the Amazon rainforest, the melting of polar ice caps, and the collapse of the critical AMOC ocean current could all occur at warming levels below 2°C.

However, societal engagement can also drive “positive tipping points” that may reduce such risks, Lenton highlights, pointing to the rapid growth of renewable energy adoption in the last decade and the increase in electric vehicle use. The swift integration of cleaner technologies has the potential to facilitate significant emissions reductions required to maintain warming under 2°C, as noted in the report.

In a statement, Lenton emphasized the need for immediate action from global leaders at the upcoming COP30 summit in Brazil, calling for accelerated emissions cuts throughout the global economy to limit the duration of global temperatures exceeding 1.5°C. “We are quickly approaching multiple tipping points that could alter our planet, leading to catastrophic consequences for humanity and nature. This necessitates immediate and unprecedented action from COP30 leaders and policymakers globally,” he urged.