Trend Ocean acidification pushed past its planetary boundary

Summary

The ocean absorbs about a quarter of human carbon dioxide emissions, which depletes carbonate ions and lowers the saturation of aragonite, the mineral many organisms use for shells and skeletons. Drawing on updated data and methods, the report judges the ocean acidification boundary to be transgressed. In 2024 the global mean surface saturation state was about 2.85, marginally below the boundary of 2.86, set at 80 percent of the pre-industrial value of 3.57. Changes are strongest at high latitudes, notably the Arctic and Southern Ocean, and some Arctic surface waters are already undersaturated, posing serious risks to calcifying life. Shell damage and dissolution are being observed in pteropods, a key link in marine food webs, while deep-water corals face increasingly corrosive conditions. Citing updated biological thresholds for vulnerable species, the report suggests the safe limit may lie closer to a 10 percent decline than 20 percent.