'Ticking Time Bomb': Study Says Ocean Acidification Crossed Planetary Boundary
"We're gambling with both biodiversity and billions in economic value every day that action is delayed," said one expert.
As this year's United Nations Ocean Conference began in France on Monday, scientists published a study showing that another "planetary boundary," or barriers that ensure the Earth is a "safe operating space for humanity," has been crossed.
Researchers said in 2023 that 6 of the 9 boundaries—biogeochemical flows, biosphere integrity, the climate, freshwater, land use, and novel entities—had been crossed. Last year, they issued a "red alert" about ocean acidification, the topic of the new study, Ocean Acidification: Another Planetary Boundary Crossed.
As the U.S. National Oceanic and Atmospheric Administration (NOAA) explains, humanity's burning of fossil fuels and land use changes have caused the concentration of carbon dioxide in the atmosphere to soar, and the ocean absorbs some of it. The resulting chemical interactions make seawater more acidic.
In the new study, scientists from NOAA, Oregon State University, and the United Kingdom's Plymouth Marine Laboratory (PML) wrote that "we improve upon the ocean acidification planetary boundary assessment and demonstrate that by 2020, the average global ocean conditions had already crossed into the uncertainty range of the ocean acidification boundary."
"This analysis was further extended to the subsurface ocean, revealing that up to 60% of the global subsurface ocean (down to 200 m) had crossed that boundary, compared to over 40% of the global surface ocean," they continued. "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."
"As our seas increase in acidity, we're witnessing the loss of critical habitats that countless marine species depend on, and this, in turn, has major societal and economic implications."
The study's lead author, North-East Atlantic Ocean Acidification Hub chair and PML professor Helen Findlay, said in a Monday statement that "looking across different areas of the world, the polar regions show the biggest changes in ocean acidification at the surface. Meanwhile, in deeper waters, the largest changes are happening in areas just outside the poles and in the upwelling regions along the west coast of North America and near the equator."
"Most ocean life doesn't just live at the surface—the waters below are home to many more different types of plants and animals. Since these deeper waters are changing so much, the impacts of ocean acidification could be far worse than we thought," Findlay noted. "This has huge implications for important underwater ecosystems like tropical and even deep-sea coral reefs that provide essential habitats and nursing refuge for many species, in addition to the impacts being felt on bottom-dwelling creatures like crabs, sea stars, and other shellfish such as mussels and oysters."
Fellow PML professor and Global Ocean Acidification Observing Network co-chair Steve Widdicombe, who provided the study authors with comments on a draft, said Monday that "ocean acidification isn't just an environmental crisis—it's a ticking time bomb for marine ecosystems and coastal economies."
"As our seas increase in acidity, we're witnessing the loss of critical habitats that countless marine species depend on, and this, in turn, has major societal and economic implications," he warned. "From the coral reefs that support tourism to the shellfish industries that sustain coastal communities, we're gambling with both biodiversity and billions in economic value every day that action is delayed."
The 2024 Planetary Boundaries report showed 6/9 boundaries breached with the 7th, Ocean Acidification, in danger. A new study shows that this too has now been crossed. The implications are huge!onlinelibrary.wiley.com/doi/10.1111/...#climatechange #oceanacidification #planetaryboundaries #oceans
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— Dr Tom Harris (@drtomharris.bsky.social) June 9, 2025 at 9:22 AM
Costa Rica and France are co-hosting the U.N. summit in the French coastal city of Nice this week. The theme is "accelerating action and mobilizing all actors to conserve and sustainably use the ocean."
Greenpeace USA oceans campaign director John Hocevar, who will be attending the meeting, said Monday that "this conference couldn't come at a more critical time. The ocean is reeling from the combined impacts of industrial fishing, plastic pollution, and climate change. And just when bold leadership is most needed, the U.S. has walked away from the global stage, opening the floodgates to destruction through a barrage of Trump administration executive orders that threaten both domestic and international waters."
"We can't afford any more delay," he stressed. "The decisions made in Nice will set the tone for key global efforts to stem the ocean crisis in the coming months, including the plastics treaty, the global ocean treaty, and deep-sea mining talks at the International Seabed Authority. Whether this conference marks a turning point or takes our oceans further down the road to ruin will depend on the strength and ambition of the commitments made by the international community to stand up for science, uphold international law, and advance environmental justice."
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. 