Nations’ impacts on the ocean and their impacts on climate change are linked, especially given the synergistic interactions among these impacts on the two largest global commons—the atmosphere and the ocean. This article argues that climate change mitigation law, as represented internationally by the United Nations Framework Convention on Climate Change and its follow-on agreements, can better reflect nations’ broader Common but Differentiated Responsibilities (CBDR) by taking ocean impacts into account—in particular, contributions to ocean acidification and to marine fishing.