A major new scientific study confirms that ocean acidification (OA)—the long-term shift in seawater chemistry caused by the absorption of atmospheric CO₂—has breached a critical planetary boundary that could lead to “unacceptable environmental change.”
The study, titled “Ocean Acidification: Another Planetary Boundary Crossed”, was led by Dr. Helen S. Findlay of the Plymouth Marine Laboratory (UK) and published in Global Change Biology in June 2025. Its findings were prominently highlighted at this year’s United Nations Ocean Conference (UNOC) in Nice.
Using cutting-edge models and observational data, the study shows that by the year 2000, global ocean conditions had already crossed a revised, more protective boundary for acidification. Meanwhile, by 2020, the original 20% planetary boundary had been breached.
The central measure is what scientists refer to as aragonite saturation state (ΩArag)—a key chemical condition that affects the ability of shell-forming organisms (such as corals, mollusks, and plankton) to survive and grow. When ΩArag drops below safe levels, organisms experience shell weakening, lower reproduction, and increased mortality. In short, “these changes result in significant declines in suitable habitats for important calcifying species, including 43% reduction in habitat for tropical and subtropical coral reefs, up to 61% for polar pteropods, and 13% for coastal bivalves,” says the study.
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Key findings include:
- As of 2020, up to 60% of the upper 200m and over 40% of the ocean surface of the ocean had passed the OA boundary.
- Suitable habitats for tropical coral reefs have declined by 43%, for polar pteropods by 61%, and for coastal bivalves (like mussels and oysters) by 13%.
The boundary was previously set at a 20% decrease in ΩArag from pre-industrial levels—but the study recommends tightening this to a 10% reduction to protect sensitive marine ecosystems.
Implications for Greece and the Mediterranean
While the study does not detail country-specific results, its global findings have clear consequences for Greece and the Eastern Mediterranean, one of the most biologically and economically important semi-enclosed seas:
- Greece’s coastal bivalve aquaculture, especially mussels and oysters, is directly threatened by acidification-induced growth and reproduction problems.
- The Mediterranean’s warmer waters and limited exchange with the Atlantic make it especially vulnerable to accelerated OA, compounding pressures from overfishing, pollution, and warming.
- Acidification may also undermine marine biodiversity hotspots and tourism-related activities such as diving and fisheries.
Only a rapid global reduction in CO₂ emissions, the study warns, can stabilize OA trends. Without it, nearly 100% of the global ocean surface will exceed safe acidity levels by 2100 under mid- to high-emissions scenarios.
This study strengthens the scientific and political case for urgent marine monitoring, climate action, and regional adaptation—especially in frontline states like Greece.
