The world’s oceans have crossed a dangerous acidity threshold, failing a key planetary health check for the first time, scientists warn.
According to the Potsdam Institute for Climate Impact Research, rising ocean acidity caused by fossil fuel emissions has pushed marine ecosystems beyond safe limits. This marks the seventh of nine planetary boundaries now transgressed, alongside climate change, deforestation, and freshwater depletion.
The 2025 Planetary Health Check reports ocean surface pH has dropped by 0.1 units since the industrial era, a 30-40% rise in acidity. This threatens coral reefs, Arctic ecosystems, and shell-forming species such as molluscs, oysters, and clams, with ripple effects for fish, whales, and human food security.
Carbon dioxide from oil, coal, and gas dissolves into seawater, forming carbonic acid and reducing calcium carbonate, essential for marine growth. The report warns this could also weaken oceans’ ability to absorb heat and remove up to 30% of atmospheric CO₂.
Levke Caesar, co-lead of the Planetary Boundaries Science Lab, described the findings as alarming: “When I allow myself to connect to it emotionally, then I am afraid. This really scares me.”
The report notes that international action has successfully restored the ozone layer and cut aerosol pollution, proving change is possible. Scientists stress urgent cuts in fossil fuels, pollution, and overfishing are needed to prevent further decline.
Potsdam 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.”
