Since the start of the Industrial Revolution, the acidity of the ocean’s…

CONCEPT

pH is a logarithmic measure of hydrogen-ion activity: a lower pH means greater acidity. Because the scale is logarithmic, a small pH decrease represents a substantial percentage increase in hydrogen-ion concentration.

Ocean acidification occurs when seawater absorbs atmospheric carbon dioxide. The dissolved carbon dioxide forms carbonic acid and shifts carbonate chemistry toward a higher hydrogen-ion concentration.

APPLICATION

1. Since the Industrial Revolution, additional anthropogenic carbon dioxide has entered the surface ocean. The average surface-ocean pH has fallen by about 0.1 unit, from roughly 8.2 to 8.1.

2. A pH decrease of 0.1 corresponds to a hydrogen-ion factor of 100.1, approximately 1.26. Thus acidity has risen by about 26%, conventionally rounded in major scientific summaries to approximately 30%.

CONTRAST

• An increase of approximately 10% is too small for the reported industrial-era change.

• A constant value conflicts with the measured decline in surface-ocean pH.

• A decrease of approximately 25% reverses the direction implied by a falling pH.

CROSS-CHECK

The logarithmic conversion from a 0.1-unit pH decline gives approximately 26%, which supports the commonly reported rounded value of an approximately 30% increase.

Therefore, the acidity of ocean surface water has increased by approximately 30%.