The social cost of carbon (SCC) is a central concept in climate change economics. This chapter explains the SCC and investigates it philosophically. As is widely acknowledged, any SCC calculation requires the analyst to make choices about the infamous topic of discount rates. But to understand the nature and role of discounting, one must understand how that concept—and indeed the SCC concept itself—is yoked to the concept of a value function, whose job is to take ways the world could be (...) across indefinite timespans and to rank them from better to worse. A great deal, therefore, turns on the details of the value function and on just what is meant by “better” and “worse.” This chapter seeks to explicate these and related issues, and then to situate them within the evolving landscape of federal climate policy in the United States. (shrink)