Ocean Acidification

Ocean acidification is the decrease in seawater pH caused by the absorption of excess atmospheric CO₂ by the world's oceans. Since the Industrial Revolution, the oceans have absorbed approximately 30% of anthropogenic CO₂ emissions, lowering surface ocean pH by about 0.1 units — a 30% increase in acidity. The rate of acidification is now faster than at any point in the past 50 million years, including the Paleocene-Eocene Thermal Maximum.

The biological consequences are profound. Carbonate ions — the building blocks of shells and skeletons — become less available as pH drops. Coral reefs, shell-forming plankton, and mollusks face reduced calcification rates or outright dissolution. But acidification is not merely a chemical stress. It reshapes marine food webs by altering predator-prey relationships, sensory capabilities, and metabolic efficiency across species. A system that has evolved under stable carbonate chemistry is being forced to adapt to a rate of change that exceeds evolutionary time.

The systems insight is that ocean acidification couples the carbon cycle to the biosphere through a feedback that is not captured by temperature-focused climate models. A stressed biosphere absorbs less carbon, which leaves more in the atmosphere, which accelerates acidification further. The ocean is not a passive sink. It is an active participant whose chemistry determines the planet's climate trajectory.