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great barrier reef
Fossil Fuels Blamed as 84% of World's Coral Reefs Hit by Worst Bleaching Event Ever Recorded
"The magnitude and extent of the heat stress is shocking," said one marine scientist.
Apr 23, 2025
A year after scientists warned the world was seeing its fourth mass coral bleaching event, rising ocean temperatures fueled by greenhouse gas emissions have now devastated 84% of Earth's coral reefs—with likely knock-on effects for about a third of all marine species and 1 billion people whose lives and livelihoods are directly impacted by the health of the "rainforests of the sea."
Coral Reef Watch at the U.S. National Oceanic and Atmospheric Administration (NOAA) released its latest data on Wednesday, showing the current bleaching event has become the most widespread on record, impacting reefs from the Indian Ocean to the Atlantic and Pacific.
The news comes three months after scientists confirmed 2024 was the hottest year on record. Last year, meteorologists also found that sea surface temperatures in the North Atlantic were about 2°F higher than the 1990-2020 average and nearly 3°F above the average in the 1980s.
Unusually warm ocean waters cause corals to expel algae that give the reefs their bright color and deliver nutrients, supporting the immense biodiversity that is normally found within the reefs. Prolonged bleaching can kill coral reefs.
"The magnitude and extent of the heat stress is shocking," marine scientist Melanie McField, the founder of the Healthy Reefs for Healthy People initiative in the Caribbean, told Reuters. "Some reefs that had thus far escaped major heat stress and we thought to be somewhat resilient, succumbed to partial mortalities in 2024."
Derek Manzello, director of Coral Reef Watch, told The Guardian that some reefs that had been considered safe from the impact of rising ocean temperatures have now been bleached.
"Some reefs that had thus far escaped major heat stress and we thought to be somewhat resilient, succumbed to partial mortalities in 2024."
“The fact that so many reef areas have been impacted," he said, "suggests that ocean warming has reached a level where there is no longer any safe harbor from coral bleaching and its ramifications."
The current coral bleaching event began in January 2023. That same year, scientists were alarmed by an ocean heatwave off the coast of Florida that rapidly bleached the continental United States' only living barrier reef.
That event prompted NOAA to introduce a new coral bleaching alert scale from Level 1—significant bleaching—to Level 5, at which point a reef is approaching mortality.
Another ocean heatwave last year threatened Australia's Great Barrier Reef, eight years after nearly half of the coral in some northern parts of the 1,400-mile reef was killed by a mass bleaching event.
But recent major bleaching events affecting specific reefs have not compared to the current widespread devastation in the world's oceans.
“Reefs have not encountered this before," said Britta Schaffelke, coordinator of the Global Coral Reef Monitoring Network, told The Guardian. "With the ongoing bleaching it's almost overwhelming the capacity of people to do the monitoring they need to do. The fact that this most recent, global-scale coral bleaching event is still ongoing takes the world's reefs into uncharted waters."
The other three mass bleaching events on record occurred from 2014-17, with 68% of the world's reefs affected; in 2010, when 37% were impacted; and in 1998, when 21% suffered bleaching.
The report from Coral Reef Watch followed the Trump administration's under-the-radar release of climate change data that minimized NOAA's findings about the level of planet-heating carbon dioxide emissions in the atmosphere. President Donald Trump also issued an executive order demanding sunset provisions for every existing energy regulation and notified companies that they can seek exemptions to clean air regulations.
Joerg Wiedenmann, a marine biologist at the Coral Reef Laboratory at the University of Southampton in England, emphasized that taking action to stop the heating of the world's oceans could protect coral reefs, the marine species they provide habitats to, and the communities they support by protecting coastlines and providing fishing and tourism jobs.
"If we manage to decrease ocean warming," Wiedenmann toldThe Washington Post, "there is always a chance for corals to recover."
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Highest Ocean Heat in 400 Years Poses 'Existential Threat' to Great Barrier Reef
"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.
Aug 08, 2024
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, toldThe 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."
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False Climate Solution of Geoengineering Could Cause Heatwaves Thousands of Miles Away
"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.
Jun 21, 2024
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, toldThe 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 Scientistreported:
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."
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