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 (PCO2) may thus lead to large cellular PCO2 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 CO2 injection as a means of controlling atmospheric CO2levels 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.