Scientists have warned that the planet crossed the global boundary for ocean acidification around the year 2020, according to a new study.
Published in Global Change Biology, the study from Plymouth Marine Laboratory, NOAA and Oregon State University concludes that a key chemical threshold—set to prevent widespread harm to marine life—has already been exceeded.
The planetary boundary for ocean acidification is defined as a 20% decline from the pre-industrial aragonite saturation state, a measure of ocean water's ability to support calcifying organisms such as corals and shellfish.
"The original boundary was characterized by two criteria: [First] that the polar regions do not reach undersaturation, and [second] that warm-water coral reefs do not fall below the marginal growth threshold," study author Helen Findlay told Newsweek in an email.
"We felt that neither of these things could be really assessed using a surface ocean global average figure without considering natural seasonal and regional variability, and so our study made the reassessment based also on regional changes."
Underestimating the Pace
Using updated models, the study found that the global average surface ocean had entered the boundary's uncertainty zone by 2020.
In deeper layers of the ocean, the findings are even more severe. At depths of 200 meters, 60% of the ocean had surpassed the acidification threshold.
Previous planetary boundary assessments, including those as recent as 2023, had judged ocean acidification to be nearing its critical limit but not yet beyond it.
The new analysis suggests that the original boundary may have underestimated the pace and reach of acidification.
It also reveals that the most affected regions include polar waters and the tropical zones that support the bulk of the world's coral reef systems.
'Now is the time'
"In our lifetimes (and by year 2100) we are committed to the ocean acidification that has already taken place," Findlay told Newsweek. "We cannot reverse that in the short term.
"Even if we were to stop emitting CO2 today, the ocean would remain at this level of ocean acidification for thousands of years."
However, Findlay noted that carbon dioxide removal and fewer emissions could speed the process up.
"Our models tell us that this is the decade for decisions," she told Newsweek. "For ocean acidification, the emissions pathways diverge around the year 2030, which means that now is the time to make the choice about how we minimize further damage."
How Ocean Acidification Happens
Ocean acidification occurs when carbon dioxide from the atmosphere dissolves into the ocean, changing the water's chemistry.
This process lowers the pH of seawater and reduces the amount of carbonate ions, which are essential building blocks for many marine creatures.
Animals like corals, oysters, clams and some types of plankton need carbonate to build their shells and skeletons. As acidification increases, it becomes harder for these organisms to grow and survive.
Findlay added that there has been misreporting that "all shellfish will die in the next 5-10 years".
"This is not the case," Findlay said. "Organisms are resilient when they are given the chance, but it is the rate of change that is important, and more likely that some local populations will survive and some may not."
Wide-Ranging Negative Effects
According to the researchers, habitat degradation has already become evident.
The study reports that suitable conditions for tropical coral reefs have shrunk by 43%, and for polar pteropods by up to 61%. Coastal regions vital for shellfish like oysters and mussels are also increasingly at risk.
Researchers propose redefining the ocean acidification boundary to a 10% decline from the pre-industrial saturation state to better protect marine biodiversity.
'Stick to the Paris Agreement targets'
When Newsweek asked about meaningful ways to combat acidification, Findlay explained, "Stop CO2 emissions! Stick to the Paris Agreement targets. Protect and restore ocean habitats and ecosystems. Minimize damage to the seafloor.
"Prevent the addition of nutrients and pollution in the coastal regions that can cause local acidification and therefore add to the overall global problem. Fund and support local communities to protect their local environment in a way that has sustainable benefits to them."
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