A recent proposal to store anthropogenic carbon dioxide in the deep ocean is assessed here with regard to the impacts on deep-living fauna. The stability of the deep-sea has allowed the evolution of species ill-equipped to withstand rapid environmental changes. Low metabolic rates of most deep-sea species are correlated with low capacities for pH buffering and low concentrations of ion-transport proteins. Changes in seawater carbon dioxide partial pressure (P(CO(2))) may thus lead to large cellular P(CO(2)) and pH changes. Oxygen transport proteins of deep-sea animals are also highly sensitive to changes in pH. Acidosis leads to metabolic suppression, reduced protein synthesis, respiratory stress, reduced metabolic scope and, ultimately, death. Deep-sea CO(2) injection as a means of controlling atmospheric CO(2) levels should be assessed with careful consideration of potential biological impacts. In order to properly evaluate the risks within a relevant timeframe, a much more aggressive approach to research is warranted.