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.”
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