. . . It’s exciting to have a real crisis on your hands when you have spent half your political life dealing with humdrum things like the environment. . . . The world’s climate is undergoing dramatic and rapid changes. Most notably, the earth has been becoming markedly warmer, and its weather has, in addition to this, become increasingly unpredictable. These changes have had, and continue to have, important consequences for human life. In this chapter, I wish to examine what is the fairest way of dealing with the burdens created by global climate change. Who should bear the burdens? Should it be those who caused the problem? Should it be those best able to deal with the problem? Or should it be someone else? I defend a distinctive cosmopolitan theory of justice, criticize a key principle of international environmental law, and, moreover, challenge the “common but differentiated responsibility” approach that is affirmed in current international environmental law. Before considering different answers to the question of who should pay for the costs of global climate change, it is essential to be aware of both the distinct kind of theoretical challenge that global climate change raises and also the effects that climate change is having on people’s lives. Section 1 thus introduces some preliminary methodological observations on normative theorizing about global climate change. In addition, it outlines some basic background scientific claims about the impacts of climate change. Section 2 examines one common way of thinking about the duty to bear the burdens caused by climate change, namely the doctrine that those who have caused the problem are responsible for bearing the burden. It argues that this doctrine, while in many ways appealing, is more problematic than might first appear and is also incomplete in a number of different ways (sections 3 through 8). In particular, it needs to be grounded in a more general theory of justice and rights.