Why have only two of the eleven original members of the Western Climate Initiative implemented a cap-and-trade system? This article compares the implementation of cap-and-trade in California and Quebec versus in New Mexico and British Columbia. Ideas around the reality of anthropogenic global warming and the legitimacy of cap-and-trade created favorable context in three jurisdictions, although institutions condition the expression of these ideas in the policy-making process. Since parliamentary institutions concentrate power, elite consensus is more important in Canada, while in the United States public opinion plays a more significant role. However, ideational factors shaped by political institutions do not explain differences in cap-and-trade implementation. Growth in shale gas production, welcomed in British Columbia and New Mexico but resisted by Quebec and marginal in California, further explain different outcomes. Ideas, mediated by institutions, are the necessary prerequisites for action, while material factors influence policy instrument choice.

Central to this special issue is the notion that the methods and conceptual tools of comparative politics can improve our understanding of global climate change politics. Building on recent advancements in the field of comparative environmental politics, the special issues offers a more comprehensive treatment of climate change politics in developed countries, emerging economies and least developed countries. In this introduction, I distil the key features of comparative politics, advocate for the more rigorous application of comparative methods in climate politics scholarship and highlight three groups of political factors—institutions, interests and ideas—that hold considerable promise in explaining climate change politics at the domestic level. The introduction concludes with an appeal to (re)think how international and domestic politics interact. Examples drawn from the articles assembled for this special issue are used to substantiate the claims made.