March 18, 2015
The last ten years have seen the growth of linkages between many of the world's cap-and-trade systems for GHGs, both directly between systems, and indirectly via connections to credit systems such as the Clean Development Mechanism. If nations have tried to act in their own self-interest, this proliferation of linkages implies that for many nations, the expected benefits of linkage outweighed expected costs. In this article, we draw on the past decade of experience with carbon markets to examine why systems have demonstrated this revealed preference for linking. Linkage is a multi-faceted policy decision that can be used by political jurisdictions to achieve a variety of objectives, and we find qualitative evidence that many economic, political, and strategic factors – ranging from geographic proximity to integrity of emissions reductions – influence the decision to link. We also identify some potentially important effects of linkage, such as loss of control over domestic carbon policies, which do not appear to have deterred real-world decisions to link.