The U.S. Clean Air Act, passed in 1970 with strong bipartisan support, was the first environmental law to give the Federal government a serious regulatory role, established the architecture of the U.S. air pollution control system, and became a model for subsequent environmental laws in the United States and globally. We outline the Act’s key provisions, as well as the main changes Congress has made to it over time. We assess the evolution of air pollution control policy under the Clean Air Act, with particular attention to the types of policy instruments used. We provide a generic assessment of the major types of policy instruments, and we trace and assess the historical evolution of EPA’s policy instrument use, with particular focus on the increased use of market-based policy instruments, beginning in the 1970s and culminating in the 1990s.

Climate change is a complex long-run phenomenon. The speed and severity with which it is occurring is difficult to observe, complicating the formation of beliefs for individuals. The authors use Google Insights search intensity data as a proxy for the salience of climate change and examine how search patterns vary with unusual local weather. The responsiveness to weather shocks is greater in states that are more reliant on climate-sensitive industries and that elect more environmentally-favorable congressional delegations. Furthermore, they demonstrate that effects of abnormal weather extend beyond search behavior to observable action on environmental issues.

In a new discussion paper, authors Richard Schmalensee, professor of economics at the Massachusetts Institute of Technology, and Robert N. Stavins, director of the Harvard Project on Climate Agreements, explore four ironic outcomes associated with the otherwise very successful sulfur-dioxide cap-and-trade system created by the Clean Air Act Amendments of 1990.

Market-approaches to reducing emissions of greenhouse gases lie at the heart of any cost-effective set of policies put forward in an international agreement—and will be considered at COP 17 in Durban in both the Kyoto and Long-term Cooperative Action discussions. Joseph Aldy and Robert Stavins "examine the opportunities and challenges associated with the major options for carbon pricing: carbon taxes, cap‐and‐trade, emission reduction credits, clean energy standards, and fossil fuel subsidy reductions."

Harvard Project Director Robert N. Stavins reviews economics research on open-access resources over the last century; the development of market-based policies to respond to commons problems; and the application of policy-relevant scholarship in economics to the "ultimate commons problem"—global climate change.

If negotiations at COP 17 in Durban fail to produce an agreement on a Kyoto second-commitment period and on a broader climate regime, linking national climate policies would become more salient as a possible de facto international climate regime. Linking cap-and-trade systems is relatively straightforward, but linking disparate policies is harder. Metcalf and Weisbach address the linkage of heterogeneous climate policies.

Federal action addressing climate change is likely to emerge either through new legislation or via the U.S. EPA's authority under the Clean Air Act. The prospect of federal action raises important questions regarding the interconnections between federal efforts and state-level climate policy developments. In the presence of federal policies, to what extent will state efforts be costeffective? How does the co-existence of state- and federal-level policies affect the ability of state efforts to achieve emissions reductions?

"Any international agreement to address climate change must rest on broad public support in developed nations for mitigation actions. We propose an international climate architecture that builds on such public support — which we hope will be forthcoming — and uses multilateral international institutions to extend its effects to countries without such "green" publics."