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ocean acidification
'Red Alert' as 7th of 9 Planetary Boundaries On Verge of Being Breached: Report
The authors found that safe planetary boundaries had already been crossed for the climate, freshwater, land use, biogeochemical flows, novel entities, and biosphere integrity—in keeping with a study in Science Advances last year. They found a "clear trend towards further transgression"—moving deeper into the danger zone, where irreversible tipping points are more likely to be triggered—in each of the six categories.
"Our updated diagnosis shows that vital organs of the Earth system are weakening, leading to a loss of resilience and rising risks of crossing tipping points," Levke Caesar, a PIK climate physicist lead author of the report, said in a statement that announced a "red alert."
The health check also showed that ocean acidification, a seventh category, has reached a dangerous precipice, putting the foundations of the marine food web at risk. Ocean acidification, which can threaten coral reefs and phytoplankton populations, is caused by the buildup of carbon dioxide from burning fossil fuels and other human activities.
Caesar said a "safe operating space" threshold for acidification could be crossed in the next few years.
"Looking at the current evolution, I'd say it’s really, really difficult to prevent that [boundary] crossing," she told Mongabay.
A graphic shows the status of nine environmental categories, four of which have been broken down into two control variables. Image from Planetary Health Check 2024. Design by Globaïa.
PIK director Johan Rockström, a co-author of the new report, helped develop planetary boundary research in the late 2000s. In a seminal 2009 paper in Nature, he and his co-authors found that three of the nine boundaries had already been crossed. That number has gradually gone up based on a series of studies over the last decade.
The planet boundary framework, which is often connected to the degrowth movement, emphasizes that the categories are interconnected.
"The interconnectedness of [planetary boundary] processes means that addressing one issue, such as limiting global warming to 1.5°C, requires tackling all of them collectively," the new report says.
Boris Sakschewski, a climate scientist who, along with Caesar, is a lead author of the report said that, "We know that all planetary boundary processes act together and each one needs protection to protect the whole system."
The consequences of continued ocean acidification, which is primarily measured by aragonite saturation, would be severe, the report warns.
Ocean acidification is approaching a critical threshold, with significant declines in surface aragonite saturation, particularly in high-latitude regions like the Arctic and Southern Ocean. These areas are vital for the marine carbon pump and global nutrient cycles, which support marine productivity, biodiversity, and global fisheries. The growing acidification poses an increasing threat to marine ecosystems, especially those reliant on calcium carbonate for shell formation.
Some researchers believe that the ocean acidification threshold has already been crossed, especially given regional variability, with cooler polar waters absorbing more carbon dioxide, causing a faster drop in pH levels.
The report was written with a general audience in mind and is not peer-reviewed, though it's based on peer-reviewed studies, the authors said.
The final pages of the report present solutions, especially agricultural. A radical overhaul of the global food system, heavily dependent on fertilizer and other harmful inputs, will be necessary to reverse the disturbing trends documented in the report, the authors wrote.
"Sometimes overlooked compared to the impacts of energy production and consumption—particularly the use of fossil fuels—the food systems we depend on are among the largest drivers of environmental degradation. The global food system is the single largest driver behind the transgression of multiple planetary boundaries," the report says.
Scientist Says Some Coral Reefs Can Be Saved 'If We Take Immediate Action'
Using computer models, researchers from Louisiana State University, Rice University, and the University of Colorado Boulder analyzed the "ominous threats" that ocean acidification and warming pose to coral reefs in the Caribbean and Gulf of Mexico under a "business as usual" emissions scenario and one in which planet-heating pollution is reduced.
Their study, published this summer in the Journal of Geophysical Research: Biogeosciences, shows that "ocean temperatures increase by 2degC-3degC over the 21st century, and surpass reported regional bleaching thresholds by midcentury."
Bleaching is when corals expel algae--with which they have a symbiotic relationship--and turn white. Though the corals are not yet dead, they are at higher risk of mortality. Mass bleaching events around the world in recent years have heightened concerns about the fate of reefs--especially given governments' inadequate plans to rapidly transition away from fossil fuels driving the global climate emergency.
Study co-author Adrienne Correa, a marine biologist and assistant professor at Rice, said Wednesday, "The fact that we're going to see these changes by 2050 is a strong wake-up call."
"We get a lot of bad news about reefs, but we can still draw hope and motivation from this," she noted. "Some of the reefs that are included in this analysis are really special, like the Flower Garden Banks, and reefs off of Cuba and in some other parts of the Caribbean where there's still really high coral cover. We can help protect and keep the high coral cover reefs we have if we take immediate action to shift how much energy we use and where we get our energy."
"There are reefs in the Gulf that are really worth saving," Correa added. "Some of the healthiest reefs that we still have in the United States are in the areas covered by these projections."
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Fueled by Climate Crisis, Planet Lost 14% of Coral Reefs in Just One Decade
Allison Lawman, a postdoctoral associate in Colorado, explained that the study shows projected coral mortality through the next century is largely tied to the number of months each year that the reefs are exposed to high marine temperatures.
"There's always one month that is the hottest of the year," Lawman said. "Let's say it's August and the average baseline temperature for that month is 29degC in the region we're studying. A 'degree heating month' in that region is any month in the future that has a higher average temperature than 29degC."
The researchers found that under the business as usual scenario, degree heating months could become the new normal by the late 2100s, with parts of the Caribbean seeing such conditions for as many as 10 months per year.
"That's a huge number of months in which corals could experience thermal stress beyond the usual levels to which they are adapted," Lawman said. "These projections are very concerning... I think the takeaway message is that the time to act is now."
Rice climate scientist and assistant professor Sylvia Dee similarly stressed the urgency of reef-saving action.
"In one case, we have more time to mitigate, and in the other we don't," she said. "People need to be aware this is coming up fast, and the time to explore mitigation techniques is now."
The areas examined by the researchers "contain more than 10% of the world's reefs and host hundreds of fish species, and they provide more than $6 billion in economic benefits courtesy of fisheries, tourism, and other ecosystem services," according to Eos. "But over the past four decades, climate change and local stressors like overfishing, pollution, and invasive species have taken a heavy toll. On average, live coral covers less than 10% of the surface of most reefs in the region."
In a summary of the study, the researchers wrote that "we hope that this work will inform and streamline mitigation efforts to protect vulnerable coral reef ecosystems and the valuable benefits and resources they provide to local communities."
The scientists' calls for action come as world leaders prepare for COP27, a United Nations climate summit set to kick off in Egypt next month.
Unprecedented Bleaching Event Portends Mass Death of World's Coral Ecosystems
The current bleaching event has already all but destroyed Australia's Great Barrier Reef, and NOAA's experts say that warm ocean temperatures will soon trigger bleaching in the northern hemisphere, "including around Hawaii, Micronesia, the Florida Keys and Puerto Rico," the Guardian reports.
Bleaching occurs when overly warm ocean waters cause coral to expel the algae living inside of it, which turns the coral white and erodes its structures, as Common Dreams has reported.
NOAA's Coral Reef Watch has described the growing swaths of bleached and dying coral as "ghostly underwater graveyards."
"It's time to shift this conversation to what we can and are doing to conserve these amazing organisms in the face of this unprecedented global bleaching event," said the director of NOAA's coral reef conservation program, Jennifer Koss, to the Guardian.
"Coral in every major reef region has already experienced severe bleaching," the newspaper adds.
" Climate change has caused global sea surface temperatures to rise by about 1C over the past century, pushing corals closer to their bleaching threshold. A strong El Nino, as well as other weather phenomena, raised the temperature further this year," the Guardian notes.
Extended bleaching events eventually kill a reef--as has already been happening to large stretches of the Great Barrier Reef.
And as with many effects of climate change, the poorest and smallest nations will likely suffer the most from the catastrophic bleaching event. Mark Eakin, director of NOAA's Coral Reef Watch, told the Guardian, "The biggest bleaching threat over the next six months is to the reefs in two U.S. freely associated states: Palau and the Federated States of Micronesia. Islanders there are very dependent on their coral reefs and diving tourism is a major contributor to their economies."
"This event may have major ecological and economic impacts on those islands," Eakin said.
Dead coral reefs "are perhaps the starkest reminders--like the melting Arctic--that a thickening blanket of greenhouse gases is irrevocably changing the face of the Earth," as Inside Climate News recently wrote.
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