The pH Scale

The pH of surface seawater averaged around 8.2 for millions of years before the Industrial Revolution, but since then has been falling rapidly due to human emissions, and subsequent ocean uptake, of carbon dioxide. A decrease in pH means the water is more acidic and makes it harder for calcifying shellfish and other marine organisms to build and maintain their shell. A drop of 0.1 pH units represents a roughly 25% increase in acidity.