In this article, carbon management is framed as a domain in which active reflection on the uncertain significance of climate change takes material form in the construction of new infrastructures of carbon accounting and carbon markets. “Carbon” refers not to a chemical, per se, but to an imaginative space of global atmospheric relations rendered material. The historical ontology of carbon and atmosphere together form a distinctive global medium, as I describe. The atmosphere as medium is manifest in the informational spaces of digital platforms meant to do work on the human subjects of climate change. I describe the carbon accounting practices of two Beijing‐based enterprises that are involved in building out the infrastructure of carbon accounting for the purpose of decarbonizing Chinese industry. Carbon is at the center of a contemporary formation that is imaginative, materialist, heavily quantified, and oriented toward the technical modification of human affairs. It supposes that humans as planetary agents have become significant in terms of collective activity that is historically recent, highly unequal, and global in scope. The human is configured not as a biological species, such as in debates on “life itself” or distinctions between humans and other species, or even in terms of an essential humanity that can provide the transcendent bonds of a moral community. Rather, carbon accounting formulates the human ecologically and geologically with an eye toward imagining the future forms these relations might take. Hence, climate change has identified the human as a contemporary problem with particular urgency.