Ocean acidification
Between 1750 and 2000, surface-ocean pH has decreased by about 0.1, from about 8.2 to about 8.1. Surface-ocean pH has probably not been below 8.1 during the past 2 million years. Projections suggest that surface-ocean pH could decrease by an additional 0.3–0.4 units by 2100. Ocean acidification could threaten coral reefs, fisheries, protected species, and other natural resources of value to society.