The amount of carbon dioxide (CO2) emitted into the atmosphere has risen about 40% above pre-industrial levels. The oceans absorb about 25% of CO2 released into the atmosphere, where the CO2 reacts with seawater to form carbonic acid, which lowers ocean pH levels, making the water more acidic.

The acidity of ocean surface waters has increased by about 30% over the last 250 years and could become nearly 150% more acidic by the end of the century if CO2 emission levels continue to increase at the current pace. Different regions of the ocean are more susceptible to an increase in acidification due to other factors such as coastal upwelling, river and glacial discharge, sea ice loss, and urbanization.

Increasing ocean acidity decreases the ability of shells and other calcium carbonate structures, such as coral skeletons, to form. Examples of sea life that are being directly affected are oysters, clams, sea urchins, shallow water corals, deep sea corals, and certain species of plankton. On a broader scale, the inability of these creatures to fully develop will also negatively impact other members of the food web that feed on them, including salmon, whales, and humans.

The illustration demonstrates the chemical process of ocean acidification.