January 5, 2026 — The past 12 months have been worrying for researchers who study the chemistry of the ocean. More and more evidence has been published showing that human activities are fundamentally altering this chemistry in an acidic direction.
At the end of 2025, it seems clear ocean acidification is pushing the largest habitat on Earth into a risky zone.
Ocean acidification is part of the global carbon cycle. When carbon dioxide dissolves in water, it forms carbonic acid. This acid releases hydrogen ions, which lower the seawater’s pH balance.
pH balance
This sliding scale of 14 points indicates the acid/alkaline balance of a solution. Position 1 indicates the highest acidity, 14 the highest alkalinity. It stands for “potential of hydrogen”, because the scale is determined by the concentration of hydrogen ions.
Carbon dioxide emitted by human activities may be largely released into the atmosphere, but it does not all stay there. Huge amounts are absorbed by the ocean. A study published in 2023 determined that the ocean absorbed 25% of anthropogenic CO2 emitted from the early 1960s to the late 2010s. This has so far saved humanity from greater global warming.
Because of the rise in atmospheric CO2 concentrations over the past century, more CO2 has been taken up by the ocean, causing it to acidify.