Ocean acidification is likely to have direct negative physiological consequences for many marine organisms, and cause indirect effects on marine ecosystems. Ocean acidification could also affect the oceans' current role as a net carbon sink by altering the oceanic calcium carbonate budget. Although ocean acidification and climate change are both caused by greenhouse gas emissions, ocean acidification is not climate change per se, and is often referred to as “the other carbon dioxide (CO₂) problem.” As the United States considers actions in response to climate change, it is critical to take into account not only the impact of CO₂ emissions on the climate but also their ramifications for ocean chemistry. The metrics that currently guide the climate change debate are dominated by strategies to reduce thermal impacts on the terrestrial environment. In this article, I examine the effects of ocean acidification and why they should help guide decisionmakers in setting CO₂ emissions goals.