Although climate change garners the bulk of headlines, ocean acidification is an equally important issue that also results from our increasing consumption of fossil fuels. As atmospheric CO₂ dissolves into the ocean, the ocean's pH decreases, making it increasingly difficult for organisms that build calcium carbonate skeletons to grow and thrive. Given that these marine calcifiers – such as corals, snails, shellfish, crustaceans, and plankton – often form the base of oceanic food webs and are habitat and food resources for larger oceanic plants and animals (including humans), ocean acidification poses a serious threat. In this article, we present a series of investigations that provide evidence that increases in anthropogenic sources of CO₂ contribute to the acidification of the ocean, and that an increasingly acidic ocean can negatively impact marine calcifiers.