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Coral Reef Tipping Point: ‘Near-Annual’ Bleaching May Occur Globally, Scientists Say

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The Great Barrier Reef, where record-high sea temperatures in February caused its most widespread coral bleaching event. JAYNE JENKINS / CORAL REEF IMAGE BANK

Tropical coral reefs are at a critical tipping point, and we've pushed them there, scientists say. Climate change may now cause previously rare, devastating coral bleaching events to occur in tropical coral reefs around the globe on a 'near-annual' basis, reported The Guardian.


In February 2020, record-high sea temperatures at Australia's Great Barrier Reef caused the most widespread coral bleaching event at the reef ever, reported NBC News. Unfortunately, this was also the third such major bleaching in five years, raising concerns over the fragile corals' ability to keep rebounding against worsening marine conditions.

To put it into perspective, there have only ever been five recorded bleaching events at the Great Barrier Reef, explained Terry Hughes, director of the Australian Research Council's Centre of Excellence for Coral Reef Studies at James Cook University in North Queensland, to NBC News. The first two were in 1998 and 2002, and then there was a 14-year gap before the 2016 and 2017 events. The latter two resulted in the death of almost half of the famed reef's corals in just two years, NBC News reported.

Scientists weren't expecting another bleaching event so soon, explained Mark Eakin, coordinator of the National Oceanic and Atmospheric Administration's Coral Reef Watch program in College Park, Maryland to NBC News. "This has never happened before. We're in completely uncharted territory."

Now, Eakin warns that the accelerating frequency may indicate something far worse. "The real concern is with this much bleaching without tropical forcing," Eakin told The Guardian. "This may be a sign we've now tipped over to near-annual bleaching in many locations."

Historically, tropical coral reefs bleach more often when the Pacific Ocean is in a phase known as El Niño, reported The Guardian. This latest bleaching on the reef has hit during a neutral phase in the cycle.

Eakin told The Guardian, "It's quite concerning that we are getting this much heat stress across the Great Barrier Reef in an Enso [El Niño southern oscillation]-neutral year."

Eakin's agency, Coral Reef Watch, monitors coral reefs across the globe, not just in Australia. Their research led Eakin to additionally conclude that there was a risk that this mass bleaching at the Great Barrier Reef could mark the start of another global-scale event, reported The Guardian.

"If we get another El Niño, the odds are almost 100% that we will see another global bleaching event," Eakin told The Guardian.

"The gap between one event and the next is shrinking, not just for the Great Barrier Reef, but reefs throughout the tropics," Hughes told NBC News. "That's important, because it takes a decade or so for a half-decent recovery of even the fastest-growing corals. The slowest ones take several decades."

Given their long recovery time, Eakin warned The Guardian, "We are seeing these events far too frequently" for reefs to recover from mass mortality of corals due to bleaching.

The news report explained that corals bleach when they sit in abnormally hot water for too long. While corals can recover from mild bleaching, severe and prolonged heat stress can kill corals.

Eakin added, "What we are seeing on the Great Barrier Reef and potentially elsewhere is really being driven just by anthropogenic climate change," reported The Guardian.

Increased greenhouse gases in the atmosphere cause the planet to warm, and 90 percent of that extra heat is taken up by oceans, explains the news report. According to CBS News, because corals are extremely sensitive to ocean temperatures, raising the water temperature by even a couple of degrees can still result in mass coral bleaching. And while bleaching does not kill the coral, it weakens them, making them vulnerable to disease, The Guardian explained.

Eakin concluded, "There's so much heat that has been absorbed in the upper ocean that all the coral reefs are much closer now to their bleaching threshold. As result, it's very easy to tip them over," reported The Guardian.

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