This chapter considers the threat of ocean acidification from the perspective of both harm to ocean ecological systems and positive climate feedbacks. A survey of current governance responses demonstrates an alarming failure. No international governance regime currently accounts for ocean acidification by requiring significant and additional reductions in CO2 emissions. In an oceans context, acidification is treated as a gradual background stressor along with a range of climate change impacts. Against this backdrop and employing the Anthropocene concept, together with emerging realization that we face a planetary emergency, this chapter proposes a radical change of approach. It proposes that we begin with emergency closure of a large swath of the ocean – namely areas beyond national jurisdiction. While not an end in itself, emergency closure of the Earth's largest ecological system is a critical place to begin confronting what the Anthropocene means, the implications for all life, and how humanity must govern itself. Change here may seed a very different understanding of what is required as we confront the reality of an Earth system as a global ecological commons on the verge of abrupt, irreversible, and destructive changes. At the very least, such an emergency response may (not will) slow the rate of accumulating harm while we formulate entirely new human responses fully commensurate with the complex and urgent existential crisis of our making.