About half of the carbon dioxide from anthropogenic sources since the beginning of the industrial revolution is no longer in the atmosphere. For a long time, it has been recognized that the oceans have been absorbing the gas, and this is often viewed positively by environmentalists, because the impact on climate change would otherwise be much larger. However, this issue of Science contains a "Perspective" by Takahashi and two related research reports, "Impact of Anthropogenic CO2 on the CaCO3 System in the Oceans", by R. A. Feely et al. and "The Oceanic Sink for Anthropogenic CO2", by C. L. Sabine et al. that indicate that the consequent increases in the concentrations of carbonate species and decreases in the pH of the oceans may adversely affect life there, both plankton like the one shown on the cover, and corals. This subject is rife with grist for chemistry courses, from density to complex equilibria. Anyone can read the abstracts of these papers, and subscribers can read the whole articles online. One more thing to worry about...