At a conference in 2019, marine biologist and coral reef conservationist Melanie McField was caught off guard by a question from another attendee: How does it feel to have dedicated your life to studying an ecosystem that will be the first one wiped off the planet?
“I’m rarely dumbfounded,” McField, who now serves as director of the Healthy Reefs for Healthy People initiative, told Gizmodo. Though she was well aware of the dire state the world’s coral reefs were in, the idea that these ecosystems could be the first to succumb to climate change came as an alarming new realization. “I just didn’t know what to say,” she said.
Today, McField is one of 160 authors of a landmark report confirming that the questioner that day may have been right. The 2025 Global Tipping Points Report, released by the University of Exeter and international partners on Sunday, finds that the world’s warm-water coral reefs have become the first Earth system to cross its thermal tipping point.
The report comes as global ministers gather in Brazil to meet in preparation for the 30th annual UN Climate Change Conference in November. During these meetings, leaders attempt to reach some consensus on the key climate issues facing the planet. The report’s authors hope their findings will help drive decision makers to take meaningful action to curb global warming.
“We need to have stubborn people at the table in these negotiations who say, ‘We want to keep coral reefs on the planet,’” McField said.
The rising threat of ocean warming
Higher ocean temperatures are forcing many of the world’s corals to expel the symbiotic algae, or zooxanthellae, that live in their tissues—a process known as coral bleaching. These algae not only give corals their signature bright colors, but also provide them with oxygen and essential nutrients through photosynthesis.
Earth is in the midst of its fourth global coral bleaching event, according to NOAA. Since January 2023, bleaching-level heat stress has impacted 84.4% of the world’s coral reefs, with scientists documenting mass coral bleaching in at least 83 countries and territories. This is the second such event in the last 10 years and the largest on record.
The good news is this: Bleached corals are not necessarily dead corals. If ocean temperatures return to a cooler state for a sustained period of time, algae can recolonize a bleached reef. The bad news, however, is that climate change is increasing the severity of bleaching events while decreasing the amount of recovery time between them. As a result, the odds of corals bouncing back are rapidly dwindling.
“This is why ocean warming is such a scary thing,” Mark Hixon, a leading coral reef expert and professor of marine biology at the University of Hawaii who was not involved in the report, told Gizmodo. “Especially now with the ocean starting to warm very, very rapidly, we’ll be seeing more frequent and more severe bleaching events.”
At what point does the global average temperature of Earth’s oceans become so warm that the majority of coral reefs won’t be able to survive bleaching events? This is where the idea of a thermal tipping point comes in. Researchers estimate the thermal tipping point for warm-water coral reefs to be 2.16 degrees Fahrenheit (1.2 degrees Celsius) of global surface warming above pre-industrial levels. The planet is already past that point.
Entering uncharted waters
Crossing this threshold doesn’t mean that all the world’s reefs are going to die tomorrow. “That’s not what we’re saying,” McField said. “We’re saying we’re in the zone where death—the tipping of the whole ecosystem—is underway.”
Each coral reef is unique, with different species, local water temperatures, non-thermal stressors, ecosystem intactness, and resilience levels. These and other factors shape a reef’s survivability. But in a warming world, all reefs—regardless of their individual conditions and characteristics—are at greater risk.
“Let’s say we’ve got 100 humans, and they all go to the doctor,” McField said. “All of them have cholesterol levels of 300—which is incredibly dangerous. They’re still going to die at different rates.”
The report finds that Earth’s global surface temperature may rise 2.7°F (1.5°C) above pre-industrial levels within the next 10 years. This is the upper range of the thermal tipping point for warm-water coral reefs.
At that point, “We’re in new territory,” McField said. Even under the most optimistic scenario, in which global warming stabilizes at 2.7°F without any overshoot, warm-water coral reefs are “virtually certain” to tip, the report states.
Where we go from here
Scientists around the world are working to protect and restore coral reefs. Some strategies center on improving coral resilience through genetic modification—selectively breeding them for resiliency traits.
“This can work to some degree, to keep from losing species entirely,” McField said.
“But when you think about how that could ever be applied on an ecosystem scale, with so little money going into on-the-ground work in reef countries… how is that going to be an economic option?”
Other strategies aim to minimize other potential stressors, like pollution or destructive fishing practices. Hixon, for example, is working to improve water quality and protect herbivorous fish species in Hawaii, which could reduce the overall strain on coral reefs and help them rebound from bleaching events.
Still, this work can’t mitigate all the effects of rapidly rising temperatures. The report states that the Earth needs stringent emission mitigation and enhanced carbon removal to bring the global average surface temperatures back down to 1.8°F (1°C) above pre-industrial levels. “These temperatures are essential for retaining functional warm-water coral reefs at meaningful scale,” the report says.
“It’s incumbent upon the scientific community to engage with stakeholders of all kinds on the threats to the reefs, how they’re accelerating, and how there are certain tangible steps we can take to try to save our reefs from loss,” Hixon said.
