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Climate Change Has ‘Permanently’ Changed the Great Barrier Reef

Scientists speculate that the era of never-ending global coral bleaching may have already arrived, decades early.

By Eric Holthaus


Documenting the dead coral after the bleaching event at Lizard Island on the Great Barrier Reef. (

Photo: The Ocean Agency/XL Catlin Seaview Survey/Richard Vevers)

It’s a tough time to be a coral reef on planet Earth. And, at the Great Barrier Reef in Australia, there’s new evidence that climate change may have already pushed the world’s most productive ecosystems into a new normal — prompting a rapid and radical re-think in conservation strategies.

“Even the most pristine, remote places can be devastated if it gets hot enough, and that’s what happened in the northern Great Barrier Reef,” says Terry Hughes, the director of the Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University.

A global bleaching event — a frequently fatal condition triggered when warmer than normal ocean temperatures cause corals to expel their tiny, symbiotic algae — is entering its third year. Scientists are urgently working with conservationists to figure out what is happening and what it all means for the future.

“The worry for those of us who deal with this stuff on a day-in, day-out basis is that our lives are now changed.”

In a new study, published Wednesday as the cover story in the journal Nature, Hughes and his colleagues — the paper includes an astounding 45 co-authors — find that 91 percent of the Great Barrier Reef has bleached at least once during three major bleaching events in 1998, 2002, and 2016. The most recent of these events — triggered in part by a strong El Niño — was so severe that there is no similar analog in the thousands of years of ancient coral cores scientists use to study past climates.

“The first widespread record of an El Niño causing coral bleaching was in 1982–83,” Hughes said. “An even bigger event, far bigger, occurred in 1998. That was the first time that the Great Barrier Reef bleached. So we went from a pre-bleaching period where El Niños were harmless, and because of the rising baseline temperature, they’ve become the triggers of bleaching events.” That rising baseline temperature is directly related to climate change.


Starfish on dying coral at Lizard Island on the Great Barrier Reef in May of 2016. (

Photo: The Ocean Agency/XL Catlin Seaview Survey/Richard Vevers)

The study’s authors further argue that, over the last decade or two, global warming has changed conditions on the Great Barrier Reef so quickly that old conservation methods no longer work. One of the study’s conclusions is that “local management of coral reef fisheries and water quality affords little, if any, resistance to recurrent severe bleaching events.”

That’s mostly because steadily warming oceans have shortened the recovery time between bleaching events. Quick-growing corals in the Great Barrier Reef require 10 to 15 years to fully recover from a mass-bleaching event, and long-lived species may require many decades. That kind of breathing room is “no longer realistic,” according to Hughes and his colleagues, as long as global temperatures keep rising. As a result, “the assemblage structure of corals is now likely to be permanently shifted at severely bleached locations in the northern Great Barrier Reef.”

A New York Timessummary puts the study’s implications in stark terms:

If most of the world’s coral reefs die, as scientists fear is increasingly likely, some of the richest and most colorful life in the ocean could be lost, along with huge sums from reef tourism. In poorer countries, lives are at stake: Hundreds of millions of people get their protein primarily from reef fish, and the loss of that food supply could become a humanitarian crisis.

In the paper, which required about a year to compile, Hughes speculates that the chances that the Great Barrier Reef returns to its former glory in our lifetime are “slim given the scale of damage that occurred in 2016 and the likelihood of a fourth bleaching event occurring within the next decade or two as global temperatures continue to rise.”


It didn’t take nearly that long.

Earlier this month, the authority that oversees the Great Barrier Reef discovered that it has begun bleaching again — just months after its worst bleaching event on record. Hughes himself will oversee a comprehensive areal survey to chronicle the damage starting on Wednesday — the same survey he conducted last year that led to the publication of the Nature study. Essentially, the planet is changing too quickly for corals — and scientists — to keep up.

“There’s something inherently different about the oceans now — and in this case about the tropical Pacific Ocean — than there was three years ago,” says Mark Eakin, coordinator of the National Oceanic and Atmospheric Administration’s Coral Reef Watch, which monitors and predicts global heat stress on coral reefs. “The worry for those of us who deal with this stuff on a day-in, day-out basis is that our lives are now changed.” Eakin is also a co-author on the new Nature study.

Eakin is not waiting around to find out. Last month, he joined an ambitious new conservation initiative called 50 Reefs, where he will serve on the scientific steering committee to help identify the 10 percent of the world’s reefs most likely to survive the next few decades. The idea is that limited conservation resources — including exotic efforts such as assisted evolution and coral farming — can then be concentrated into preserving those reefs as the “seed into the future” that may eventually be used to restock areas that are lost. “We’re going into it with a realization that we’re going to lose most of the world’s coral reefs,” Eakin said.

But even radical conservation efforts will only buy so much time. The Nature study’s authors are clear about the best solution: “urgent and rapid action to reduce global warming” is the only hope in preserving the world’s coral reefs largely intact.

“We’re moving into an era of regular or continual bleaching of corals,” said Eakin — a state that, until recently, scientists didn’t expect to happen until the mid-2050s. “The big question in my mind right now is, have we just made a switchover into that mode? This global bleaching event that started in June 2014 may never end.”