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"In the absence of rapid, coordinated, and ambitious global action to combat climate change, we will likely be witness to the demise of one of Earth's great natural wonders," the authors of a study in Science wrote.
The Great Barrier Reef recently experienced the highest ocean temperatures in at least four centuries and faces an "existential threat" due to repeated mass coral bleaching episodes, a study published Wednesday in Science found.
The network of coral reefs off of Australia—the world's largest living structure—has faced five of the six hottest three-month periods of average surface temperature ever recorded just since 2016, each of which was accompanied by devastating coral bleaching.
Ocean temperatures around the reef reached a record-breaking extreme from January to March this year, with the three-month mean temperature 1.73°C higher than the pre-1900 average, according to the study, authored by researchers based in Australia.
The study includes climate modeling that attributes the temperatures to fossil fuel-driven carbon emissions, and concludes that urgent climate action is needed.
"This attribution, together with the recent ocean temperature extremes, post-1900 warming trend, and observed mass coral bleaching, shows that the existential threat to the Great Barrier Reef ecosystem from anthropogenic climate change is now realized," the study says.
"In the absence of rapid, coordinated, and ambitious global action to combat climate change, we will likely be witness to the demise of one of Earth's great natural wonders," the authors also wrote.
The Great Barrier Reef is under critical pressure, with warming sea temperatures and mass coral bleaching events threatening to destroy the remarkable ecology, biodiversity, and beauty of the world’s largest coral reef, according to research in @nature. https://t.co/67bXgmfTEn
— Robin Hicks (@RobinHicks_) August 8, 2024
The researchers estimated the surface temperatures for 1618-1899 by using a reconstruction method based on drilling into coral skeletons and analyzing the chemical makeup. For the period from 1900 to 1995, they used both the reconstruction method and measurements by modern instruments, and for the last 30 years they used instrumental data.
They found that temperatures were relatively stable until 1900 but have climbed steadily since, especially since 1960.
The trend has culminated in a series of bleaching events, in which stressed corals expel the microscopic algae in their tissues and become transparent or white. Without the helpful algae, which live inside them symbiotically, corals are at risk of disease and death.
In interviews with journalists, the study authors spoke about the severity of the threat to the Great Barrier Reef and the urgent need for climate action.
"The heat extremes are occurring too often for those corals to effectively adapt and evolve," Ben Henley, a paleoclimatologist at the University of Melbourne and lead author of the study, told The New York Times. "If we don't divert from our current course, our generation will likely witness the demise of one of Earth's great natural wonders, the Great Barrier Reef."
Henley said he snorkeled with his father on the Great Barrier Reef as a child.
"You can't even take in the diversity," he said. "It's a kaleidoscope of color, it's absolutely spectacular."
He said he worries that his own 2-year-old daughter may not be able to enjoy the same experience.
"In her childhood years the reef is likely to see immense destruction," he said.
He called for strong global action so that his daughter and members of her generation could "marvel at the reef in their lifetimes."
Helen McGregor, a scientist at the University of Wollongong and study co-author, told the BBC the new research "could send a huge signal to the world about how grave the problem is."
"We know what we need to do," she added. "We have international agreements in place [to limit global temperature rise]."
Scientists not involved in the study agreed about the importance of the research, not just for the Great Barrier Reef but for coral reefs more generally.
"It's a stunningly important summary of the history of the world's largest reef system," Stephen Palumbi, a marine biologist at Stanford University, told the Times. "The paper lays out the danger that corals all around the world face from this heat."
"We need more regional geoengineering modeling studies like this work to characterize these unintended side effects before they have a chance to play out in the real world," said the study's lead author.
A study published Friday found that a cloud engineering technique designed to cool parts of the western United States could inadvertently stoke heatwaves from North America to Europe, underscoring why many scientists reject geoengineering as a false climate solution.
The study, published in the journal Nature Climate Change, concludes that marine cloud brightening (MCB)—"a geoengineering proposal to cool atmospheric temperatures and reduce climate change impacts"—in the "remote mid-latitudes or proximate subtropics" of the northern Pacific Ocean—would decrease "the relative risk of dangerous summer heat exposure by 55% and 16%, respectively."
However, the researchers found that regions including Africa's Sahel, central North America, Europe, and northeastern Asia would "experience exacerbated heat stress and hotter summers with MCB than would otherwise occur under global warming."
Additionally, the study shows that MCB would be less effective over time and could "even increase heat stress in the western United States" and beyond by mid-century.
University of California San Diego researcher Jessica Wan, who led the study, told The Guardian that MCB "can be very effective for the U.S. West Coast if done now, but it may be ineffective there in the future and could cause heatwaves in Europe."
The study's authors said the paper's findings are especially troubling given the dearth of international MCB regulation.
"There is really no solar geoengineering governance right now. That is scary," said Wan. "Science and policy need to be developed together. We don't want to be in a situation where one region is forced to do geoengineering to combat what another part of the world has done to respond to droughts and heatwaves."
As New Scientist reported:
The MCB experiments that have taken place so far in Australia and California haven't been of a sufficiently large scale to cause detectable climate effects, but they suggest that regional geoengineering could be closer to reality than previously thought, says Wan. "We need more regional geoengineering modeling studies like this work to characterize these unintended side effects before they have a chance to play out in the real world."
In Australia, researchers are experimenting with geoengineering techniques in an effort to cool the Great Barrier Reef and decelerate its bleaching. In California, scientists from the University of Washington sprayed sea salt flecks over a decommissioned aircraft carrier in the San Francisco Bay in hushed testing that was halted by the city of Alameda last month over safety concerns.
"We strongly welcome Alameda City Council's unanimous decision to say no to the first open-air marine cloud brightening experiment in the U.S.," Mary Church of the Center for International Environmental Law said after the halt. "Key concerns raised by council members focused on lack of sufficient information, notice, and transparency. The rejection rightfully reflects the gravity of what's at stake for both local and global communities."
"We are really running out of time. We need to reduce our emissions immediately," one expert warned. "We cannot expect to save the Great Barrier Reef and be opening new fossil fuel developments."
Marine conservationists warned Thursday that Australia's Great Barrier Reef may be suffering its worst-ever coral bleaching event amid record ocean heat fueled by the worsening climate emergency.
The Australian Marine Conservation Society (AMCS) said that bleached corals have been found at depths of up to nearly 60 feet, and "some corals are starting to die as they face record marine heatwaves."
"Corals bleach when they are stressed by warmer waters for an extended period of time—during marine heatwaves, which are driven by climate change," AMCS explained. "They expel the algae that inhabit them, which is their main energy source and they starve, sometimes to death."
Data collected from aerial surveys shows that 75% of the Great Barrier Reef has bleached during the current event, which the U.S. National Oceanic and Atmospheric Administration warned last month is likely to be "the worst bleaching event" ever observed in the world.
"This new footage shows extensive coral bleaching in southern reefs, but there are images from the central and northern parts that show bleaching is extensive and severe in some of those areas too," AMCS Great Barrier Reef campaign manager Lissa Schindler said in a statement.
"The Great Barrier Reef is experiencing an unprecedented fifth mass coral bleaching in eight years," Schindler added. "This is worse than the past two mass bleaching events—in 2020 and 2022—and we may discover as bad as the worst bleaching on record in 2016."
According to AMCS:
Some regions in the southern reef have experienced unprecedented marine heatwaves, with elevated water temperatures for a record 14.57 degree heating weeks (DHW)—a measure of excessive heat over time—breaking the previous record of 11.8 DWH set in April 2020, according to data from the U.S. government's world-leading ocean agency, the National Oceanic and Atmospheric Administration.
"I feel devastated. This bleaching event is the worst I have seen. It's a severe bleaching event," said Selina Ward, a coral reef expert and the former academic director of the University of Queensland's Heron Island Research Station.
Ward, who reported extensive bleaching at all 16 sites she just visited along the southern Great Barrier Reef, added: "I've been working on the reef since 1992 but this I'm really struggling with. The diversity of species involved has been hard to deal with. Look at bleached areas, there are many different species that are bleached—many of which are pretty resistant to bleaching."
It's not just Australia or even the Southern Hemisphere. Following the planet's hottest summer on record last year, the Caribbean suffered its worst recorded bleaching event.
The last global bleaching occurred in 2014-17, when scientists say approximately 15% of all reefs experienced major coral deaths. Nearly a third of the Great Barrier Reef's coral perished during that event—a die-off that could be eclipsed this time.
"This bleaching event again brings us to the question, what are we doing to stop the reef from being lost?" Ward asked. "I can't help but wonder what it is going to take for the right decisions to be made."
"We are really running out of time. We need to reduce our emissions immediately," she added. "We cannot expect to save the Great Barrier Reef and be opening new fossil fuel developments. It's time to act and there are no more excuses."