Ocean acidification describes the ongoing decrease in the pH of the Earth’s oceans, caused by their uptake of anthropogenic carbon dioxide from the atmosphere. Anthropogenic effects or processes are those derived from human activities, as opposed to effects or processes that occur in the natural environment without human influences.

Between 1751 and 2004 surface ocean pH is estimated to have dropped from 8.25 to 8.14. While the full ecological consequences of these changes are still uncertain, it appears likely that calcifying species will be adversely affected.

Present evidence suggests that dramatic changes in the marine environment over the next 100-200 years can be avoided only with early and deep reductions in carbon dioxide emissions.