This essay provides one economist’s perspective on the two-decade evolution of the field of environmental economics, by tracing it through personal reflections on the professional path that has led to my research and writing. Also, the article summarizes the highlights of some of my research and writing during this period.

The Intergovernmental Panel on Climate Change (IPCC) is broadly viewed as the world’s most legitimate scientific assessment body that periodically assesses the economics of climate change (among many other topics) for policy audiences. However, growing procedural inefficiencies and limitations to substantive coverage have made the IPCC an increasingly unattractive forum for the most qualified climate economists. Drawing on our observations and personal experience working on the most recent IPCC report, published last year, we propose four reforms to the IPCC’s process that we believe will lower the cost for volunteering as an IPCC author: improving interactions between governments and academics, making IPCC operations more efficient, clarifying and strengthening conflict of interest rules, and expanding outreach. We also propose three reforms to the IPCC’s substantive coverage to clarify the IPCC’s role and to make participation as an author more intellectually rewarding: complementing the IPCC with other initiatives, improving the integration of economics with other disciplines, and providing complete data for policymakers to make decisions. Despite the distinct characteristics of the IPCC that create challenges for authors unlike those in any other review body, we continue to believe in the importance of the IPCC for providing the most visible line of public communication between the scholarly community and policymakers.

The Intergovernmental Panel on Climate Change (IPCC) has proven its value as an institution for large-scale scientific collaboration to synthesize and assess large volumes of climate research for use by policy-makers, as well as for establishing credibility of findings among diverse national governments. But the IPCC has received considerable criticism of both its substance and process. The new IPCC leadership to be elected in October could help guide the IPCC to a clear, shared understanding of future objectives and could shape procedural reforms. We identify key opportunities for reform by addressing two related questions: Is the IPCC doing the right things? Is the IPCC doing things right?

The Durban Platform for Enhanced Action negotiations are likely to lead to a Paris outcome that embodies a hybrid climate policy architecture, combining top-down elements, such as for monitoring, reporting, and verification, with bottom-up elements, including ‘Intended Nationally Determined Contributions’ from participating countries, detailing plans to reduce emissions, based on national circumstances. For such a system to be cost-effective – and thus more likely to embody greater ambition – a key feature will be linkages among regional, national, and sub-national climate policies. By linkage, we mean formal recognition by a mitigation programme in one jurisdiction of emission reductions undertaken in another jurisdiction for the purposes of complying with the first jurisdiction's requirements. The Paris outcome could play at least four different roles with respect to linkage of heterogeneous policy instruments. First, it could discourage linkage, either by not allowing countries to count international transfers toward their mitigation contributions, or by limiting the number or types of transferred units that can be counted for compliance purposes. Second, it could be silent on the topic of linkage, creating legal and regulatory uncertainty about whether international transfers are allowed. Third, it could expressly authorize linkage but not provide any further details about how linkage should occur, leaving it to future United Nations Framework Convention on Climate Change negotiating sessions to work out the details or to national governments to develop bilateral or multilateral linkage arrangements. Finally, the Paris outcome could establish institutional arrangements and rules that facilitate and promote linkage. We examine how a future international policy architecture could help facilitate the growth and operation of a robust system of international linkages. Several design elements merit serious consideration for inclusion in the Paris outcome, either in the core agreement or by establishing a process for subsequent international elaboration. At the same time, including detailed linkage rules in the core agreement is not desirable because this could make it difficult for rules to evolve in light of experience.Policy relevanceThese findings have implications for the efficient and effective design of an international climate policy architecture by detailing the role that linkage can play in supporting heterogeneous climate policies at the regional, national, and sub-national levels.

On February 18-20, 2015, twenty-four experts gathered in Berlin to explore approaches to improving the process by which research on climate change is assessed – with a focus on the social-sciences (economics, political science, policy studies). The workshop was sponsored by the Fondazione Eni Enrico Mattei, the Harvard Project on Climate Agreements, the Mercator Research Institute on Global Commons and Climate Change, and the Stanford Environmental and Energy Policy Analysis Center. Leaders of three of the sponsoring organizations, Carlo Carraro (FEEM), Charles Kolstad (Stanford University), and Robert Stavins (Harvard Kennedy School), have prepared a memorandum drawing from the workshop. The memo describes the specific challenges and opportunities facing the Intergovernmental Panel on Climate Change (IPCC) and provides recommendations for improving the IPCC's process of assessing scientific research on climate change.

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.Policy relevanceThese findings have implications for the future role that decentralized linkages may play in international climate policy architecture. The Kyoto Protocol has entered what is probably its final commitment period, covering only a small fraction of global GHG emissions. Under the Durban Platform for Enhanced Action, negotiators may now gravitate toward a hybrid system, combining top-down elements for establishing targets with bottom-up elements of pledge-and-review tied to national policies and actions. The incentives for linking these national policies are likely to continue to produce direct connections among regional, national, and sub-national cap-and-trade systems. The growing network of decentralized, direct linkages among these systems may turn out to be a key part of a future hybrid climate policy architecture.

In June, the Obama Administration unveiled its proposal for a Clean Power Plan, which it estimates would reduce carbon dioxide (CO2) emissions from existing U.S. power plants 30% below 2005 levels by 2030 (see the chart). Power plant emissions have declined substantially since 2005, so the plan is seeking reductions of about 18% from current levels. Electricity generation accounts for about 40% of U.S. CO2 emissions.