There is widespread agreement among most economists that economy-wide carbon pricing will be a necessary (although not necessarily sufficient) component of any policy that can achieve meaningful and cost-effective CO₂ reductions in large, complex economies. But there is less agreement about which of two carbon pricing instruments will be better. Some support carbon taxes, while others favor cap-and-trade. How do these two pricing approaches compare? In this survey and synthesis of theory and experience, I show that when carbon taxes and carbon cap-and-trade systems are designed in ways that make them truly comparable, their characteristics and outcomes are similar and, in some respects, fully equivalent. But the two approaches can perform quite differently along some specific dimensions, sometimes favoring taxes and sometimes cap-and-trade. The key differences in performance depend on details of program design. Indeed, what appears at first glance to be a dichotomous choice between two distinct instruments can turn out to be a choice of specific design elements along a policy continuum.

The seminal contributions of William Nordhaus to scholarship on the long-run macroeconomics of global climate change are clear. Much more challenging to identify are the impacts of Nordhaus and his research on public policy in this domain. We examine three conceptually distinct pathways for that influence: his personal participation in the policy world; his research’s direct contribution to the formulation and evaluation of public policy; and his research’s indirect role informing public policy. Many of the themes that emerge in this assessment of the contributions of one of the most important economists to have worked in the domain of climate change analysis apply more broadly to the roles played by other leading economists in this and other policy domains.

The Paris Agreement to the United Nations Framework Convention on Climate Change has achieved one of two key necessary conditions for ultimate success—a broad base of participation among the countries of the world. But another key necessary condition has yet to be achieved—adequate collective ambition of the individual nationally determined contributions. How can the climate negotiators provide a structure that will include incentives to increase ambition over time? An important part of the answer can be international linkage of regional, national, and sub-national policies, that is, formal recognition of emission reductions undertaken in another jurisdiction for the purpose of meeting a Party’s own mitigation objectives. A central challenge is how to facilitate such linkage in the context of the very great heterogeneity that characterizes climate policies along five dimensions: type of policy instrument, level of government jurisdiction, status of that jurisdiction under the Paris Agreement, nature of the policy instrument’s target, and the nature along several dimensions of each Party’s Nationally Determined Contribution. We consider such heterogeneity among policies, and identify which linkages of various combinations of characteristics are feasible; of these, which are most promising; and what accounting mechanisms would make the operation of respective linkages consistent with the Paris Agreement.

International cooperation to address the threat of climate change has become more institutionally diverse over the past decade, reflecting multiple scales of governance and the growing inclusion of climate change issues in other policy arenas. Cooperation under the United Nations Framework Convention on Climate Change has continued to evolve from the 1997 Kyoto Protocol to the 2015 Paris Agreement, while other governmental and private sector international fora for cooperation have arisen. As the level of activity in international cooperation on climate change mitigation has increased, so too has the related scholarly literature. In this review, we synthesize the literature on international climate change cooperation and identify key policy implications, as well as those findings most relevant for the research community. Our scope includes critical evaluation of the organization and implementation of agreements and instruments, retrospective analysis of cooperative efforts, and explanations of successes and failures.