This paper is mostly about conceptualizing the problem of high-temperature catastrophic damages and giving some rough sense of the magnitudes involved via particular numerical examples. It is less about giving decisive numerical values for actual practical policy advice, although some policy implications will become apparent.

This paper describes and evaluates the system for trading CO2 emission permits introduced by the European Union to encourage the reduction of greenhouse gas emissions to help abate climate change. This system represents a live example of a functioning trading system under the so-called cap-and-trade approach to limiting greenhouse gas emissions.

This paper reexamines responsibility for climate change. Claims of responsibility are based on legal and ethical principles concerning liability for wrongdoing. They are, in essence, tort claims. Tort-law principles might be used in actual legal disputes, to make quasi-legal arguments in a negotiation, or to simply claim moral wrongdoing by a set of actors. The goal, therefore, will be to examine whether tort-law or similar theories of obligation apply to past greenhouse gas emissions

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.

We describe three essential elements of an effective post-2012 international global climate policy architecture: a means to ensure that key industrialized and developing nations are involved in differentiated but meaningful ways; an emphasis on an extended time path of targets; and inclusion of flexible market-based policy instruments to keep costs down and facilitate international equity. This architecture is consistent with fundamental aspects of the science, economics, and politics of global climate change; addresses specific shortcomings of the Kyoto Protocol; and builds upon the foundation of the United Nations Framework Convention on Climate Change.

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?

The authors compare the targets and actions to which countries have committed under the Copenhagen Accord. The Accord allows participating countries to express their commitments to reduce greenhouse-gas (GHG) emissions in a variety of ways—most broadly, through economy-wide quantified emissions targets for developed countries and mitigation "actions" by developing countries. These are difficult to compare. However, even mitigation commitments that look similar can require very different levels of effort in different countries, and commitments that produce similar economic outcomes can look inequitable. These variations in effort and equity depend on historical patterns of energy use, marginal costs of greenhouse-gas abatement, choice of base year, methods for determining "business as usual" projections, and other factors.

Different international regimes are built from legal instruments that vary in terms of whether they are multilateral or bilateral. We investigate the reasons for such variation. The choice between multilateralism and bilateralism is a function of the trade-off between each instrument's relative flaw-multilateralism is wasteful in incentives whereas bilateralism multiplies transaction costs. We illustrate some of these propositions by looking at four regimes: foreign direct investment, human rights, climate change, and international trade.

There is no integrated, comprehensive regime governing efforts to limit the extent of climate change. Instead, there is a regime complex: a loosely coupled set of specific regimes. We describe the regime complex for climate change and seek to explain it, using functional, strategic, and organizational arguments. It is likely that such a regime complex will persist: efforts to build an effective, legitimate, and adaptable comprehensive regime are unlikely to succeed. Building on this analysis, we argue that a climate change regime complex, if it meets specified criteria, has advantages over any politically feasible comprehensive regime, particularly with respect to adaptability and flexibility. These characteristics are particularly important in an environment of high uncertainty, such as in the case of climate change where the most demanding international commitments are interdependent yet governments vary widely in their interest and ability to implement such commitments.