The world’s oceans have crossed a critical acidity threshold for the first time, according to the Potsdam Institute for Climate Impact Research.
The 2025 Planetary Health Check revealed that ocean surface pH has dropped by about 0.1 units since the industrial era, a 30–40% rise in acidity. This places marine ecosystems beyond safe limits and makes ocean health the seventh of nine planetary boundaries to be transgressed.
Cold-water corals, tropical reefs, and Arctic ecosystems are particularly vulnerable. Increased acidity, caused by fossil fuel emissions, reduces calcium carbonate, harming species that rely on it for shells and skeletons. This threatens food chains from oysters and clams to salmon and whales, with consequences for human food security and coastal economies.
Oceans absorb about 25–30% of atmospheric carbon dioxide and act as the planet’s main heat buffer. Scientists warn that weakening this function could accelerate the climate crisis.
The report stressed that other breached boundaries, including climate change, land use, and freshwater systems, are worsening. Levke Caesar of the Planetary Boundaries Science Lab said: “Looking at this data, when I allow myself to connect to it emotionally, then I am afraid. This really scares me.”
Researchers emphasised solutions remain, from phasing out fossil fuels to reducing pollution and better fisheries management. Past successes like the Montreal Protocol and reduced aerosol pollution show that coordinated global action can reverse damage.
Institute director Johan Rockström said: “Even if the diagnosis is dire, the window of cure is still open. Failure is not inevitable; failure is a choice.”
