Vibrant coral reefs are more than pretty: They’re economic mainstays, massive ecosystems and world treasures. The United Nations’ cultural and scientific organization, Unesco, even counts 29 of them as world heritage sites. But now, reports Dennis Normile for Science, the future of those heritage reefs is in question. A new report suggests they could cease to function by 2100.
The sobering report released by the United Nations Educational, Scientific, and Cultural Organization’s World Heritage Center is the first of its kind, showing how climate change might impact 29 coral reefs around the world in the context of world heritage.
The study’s conclusions are dramatic. Seventy-two percent of world heritage-listed reefs were affected by the recent coral bleaching event, the agency concludes. If water temperatures continue to rise due to “business-as-usual” carbon dioxide emissions, none of the reefs will host functioning ecosystems by the end of the century. If the reefs disappear, the loss will not only gut the $1 trillion economy centered on reef tourism and fishing, but destroy part of the “common heritage of humanity,” Unesco reports.
The warning may sound dire, but it tracks with recent observations of the world’s longest recorded coral bleaching event. As Smithsonian.com reports, the bleaching event—the third on record—seems to be ending. The bleaching event began in 2015 and is predicted to fade this summer. During that time, it exposed a full 70 percent of the world’s reefs to bleaching temperatures. In a press release, the National Oceanic and Atmospheric Administration called the third event the “most widespread, longest, and perhaps most damaging on record.” Though scientists are still working to figure out how much coral was lost, they think the event decimated large portions of coral reefs worldwide. One portion of the Great Barrier Reef, for example, sustained 70 percent losses during the coral bleaching event, and at least 29 percent of the reef was damaged in 2016.
Bleaching takes place when warm water temperatures cause coral to expel the algae with which they live in a symbiotic relationship. As the algea leave, so does the coral’s color, leaving reefs pale and vulnerable to disease, structural damage and reproductive problems. The study warns that 25 of the 29 reefs will experience bleaching twice a decade by 2040, posing threats to existing and future corals.
Some coral survives bleaching and can even bounce back, though reef resilience depends on the depth, available nutrients and even shape of corals. Climate change caused by greenhouse gas emissions can hurt coral in other ways. Extreme weather, for example—predicted to increase with a warming atmosphere—can cause storm surges that damage coral in shallow waters.
Corals are not the only world heritage sites under threat. As Smithsonian.com reported earlier this year, over 100 world heritage sites face damage or destruction due to human-caused climate change.
The report’s gloomy predictions reflect the real dangers faced by coral, but might not be enough to spur action, reports Normile. A draft decision that responds to the report delays any response until at least 2018, he reports, even though some scientists say there’s no time to lose. But even the promise of future action is better than no action—and until then, it’s important to spread the word about how climate change might affect the world’s priceless corals.