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Ocean Acidification Hits Critical Threshold: Urgent Action Needed Now
Guest Contributor
Ocean acidification has long been a quiet companion to climate change, but a new study reveals it’s now reached a critical threshold—one that could have profound consequences for marine ecosystems and coastal economies. According to scientists from the UK’s Plymouth Marine Laboratory (PML), the National Oceanic and Atmospheric Administration, and Oregon State University, the world’s oceans crossed the “planetary boundary” for acidification around 2020. This alarming development, based on 150 years of data, suggests that the health of marine life is deteriorating faster than previously understood.
Ocean acidification occurs when the ocean absorbs carbon dioxide from the atmosphere. This CO₂ reacts with seawater, lowering its pH and reducing the availability of calcium carbonate—a compound essential for many marine organisms to form shells and skeletons. The term “planetary boundary” refers to the safe operating limits of Earth’s natural systems. Crossing these boundaries increases the risk of irreversible environmental shifts. Until recently, acidification hadn't been considered one of the breached limits, but this new research shows that’s no longer the case.
The findings are sobering. The study determined that the concentration of calcium carbonate in seawater has dropped more than 20% from preindustrial levels in many areas, which is the threshold for the planetary boundary. By 2020, global ocean conditions had already approached or exceeded this limit. The situation is even more dire below the surface. At depths of 200 meters, 60% of ocean waters had already crossed the safe boundary, according to the researchers.
“Most ocean life doesn’t just live at the surface,” said Prof Helen Findlay of PML. She explained that deeper waters host a vast array of marine species, many of which are critical to the functioning of underwater ecosystems. As these waters become more acidic, the survival of these species becomes more uncertain. Coral reefs—both tropical and deep-sea—are particularly vulnerable. These ecosystems serve as vital habitats and breeding grounds for numerous marine animals.
Prof Steve Widdicombe, also from PML and co-chair of the Global Ocean Acidification Observing Network, described the situation as a “ticking timebomb.” He emphasized that ocean acidification is not just an environmental issue, but a direct threat to marine biodiversity and the human economies that depend on it. The study’s comprehensive approach—analyzing ice core data, chemical measurements, computer modeling, and biological studies—offers one of the clearest pictures yet of how dramatically ocean chemistry has changed.
The effects on marine life are already evident. Species that rely on calcium carbonate, such as corals, oysters, mussels, and tiny sea butterflies, are struggling to maintain their shells and skeletons. This leads to reduced growth, impaired reproduction, and higher mortality rates. These organisms are foundational to marine food webs, and their decline could ripple across entire ecosystems.
I found this detail striking: the deeper scientists looked into the ocean, the more troubling the data became. It's a reminder that the visible surface of the sea tells only part of the story. The unseen depths are undergoing changes that could reshape marine life as we know it.
Jessie Turner, director of the International Alliance to Combat Ocean Acidification, who was not involved in the study, echoed the urgency. “We are running out of time and what we do—or fail to do—now is already determining our future,” she said. Turner pointed out that suitable habitats for many key species have already been lost and stressed that acidification must be integrated into mainstream environmental policy.
While the study underscores the need to reduce global carbon dioxide emissions as the only long-term solution, it also highlights the importance of targeted conservation. Protecting the most vulnerable species and regions could help buffer some of the immediate impacts. This dual approach—mitigating emissions while strengthening local resilience—may be the best path forward in the face of such an urgent challenge.
As the world grapples with the broader climate crisis, this research serves as a clear signal that ocean acidification can no longer be treated as a secondary concern. The oceans, which have long absorbed the brunt of human-made carbon emissions, are reaching a point where their ability to sustain life is under serious threat. The time to act, scientists warn, is now.