The world’s oceans have failed a key planetary health check for the first time, with scientists warning of severe consequences for marine ecosystems and human societies.
The Potsdam Institute for Climate Impact Research reported that ocean acidity has crossed a critical threshold, making it the seventh of nine planetary boundaries to be transgressed. The change is driven primarily by fossil fuel emissions, which release carbon dioxide that dissolves in seawater, forming carbonic acid and reducing calcium carbonate levels.
Since the industrial era, ocean surface pH has dropped by 0.1 units, a 30-40% rise in acidity. This threatens corals, shellfish, molluscs, and other organisms that form the base of the marine food chain, with cascading risks for species such as salmon and whales, as well as for human food security.
The 2025 Planetary Health Check highlighted that mass coral bleaching, cold-water coral collapse, and threats to Arctic ecosystems are becoming increasingly likely. Scientists warn that rising acidity could also undermine the ocean’s ability to absorb 25-30% of global carbon dioxide emissions, weakening its role as the planet’s main climate stabiliser.
Other breached planetary boundaries – including climate change, land use, biosphere integrity, and freshwater use – continue to worsen. Levke Caesar, co-lead of the Planetary Boundaries Science Lab, admitted the findings were frightening: “Looking at this data, when I allow myself to connect to it emotionally, then I am afraid. This really scares me.”
Despite the alarming diagnosis, experts stressed that urgent action can reverse the trend. Cutting fossil fuel use, curbing pollution, and strengthening fisheries management remain vital. They pointed to international agreements such as the Montreal Protocol as proof that global cooperation can restore planetary systems.
Johan Rockström, director of the Potsdam Institute, said: “We are witnessing widespread decline in the health of our planet. But this is not an inevitable outcome. Even if the diagnosis is dire, the window of cure is still open. Failure is not inevitable; failure is a choice.”
