Unprecedented, man-made trends in ocean's acidity

Nearly one-third of CO₂ emissions due to human activities enters the world's oceans. By reacting with seawater, CO₂ increases the water's acidity, which may significantly reduce the calcification rate of such marine organisms as corals and mollusks. The extent to which human activities have raised the surface level of acidity, however, has been difficult to detect on regional scales because it varies naturally from one season and one year to the next, and between regions, and direct observations go back only 30 years.

Combining computer modeling with observations, an international team of scientists concluded that anthropogenic CO₂ emissions over the last 100 to 200 years have already raised ocean acidity far beyond the range of natural variations. The study is published in the January 22 online issue of Nature Climate Change.