Coalition Formation in a Global Warming Game: How the Design of Protocols Affects the Success of Environmental Treaty-Making

We combine the newest concepts of non-cooperative coalition theory with a computable general equilibrium model close to the seminal RICE-model of Nordhaus and Yang (1996) to determine stable coalition structures in a global warming game. We consider three coalition games that allow for the formation of multiple coalitions. The coalition games represent different designs of climate treaty protocols. Counterintuitively, it turns out that treaties based on a unanimous decision rule and exclusive membership lead to superior outcomes than treaties with open membership. We also demonstrate that if coalition formation is not restricted to a single coalition, as this has been done previously in the literature, coalition structures with multiple coalitions will emerge in equilibrium. Most of the regional agreements are superior to single agreements. Moreover, our findings confirm those derived from simpler theoretical models that a cleverly designed transfer scheme can foster cooperation and that from the number of participants the success of a treaty cannot be inferred. They also support a conjecture of theory that in the case of greenhouse gases stable coalition structures (partial cooperation) can close the gap between the global optimum (full cooperation) and the Nash equilibrium (no cooperation) by a substantial amount.design of climate treaty protocol, coalition formation, non-cooperative game theory

An Almost Ideal Sharing Scheme for Coalition Games with Externalities

We propose a class of sharing schemes for the distribution of the gains from cooperation for coalition games with externalities. In the context of the partition function, it is shown that any member of this class of sharing schemes leads to the same set of stable coalitions in the sense of d’Aspremont et al. (1983). These schemes are “almost ideal” in that they stabilize these coalitions which generate the highest global welfare among the set of “potentially stable coalitions”. Our sharing scheme is particularly powerful for economic problems that are characterized by positive externalities from coalition formation and which therefore are likely to suffer from severe free-riding.coalition games, partition function, externalities, sharing schemes

An Empirical Assessment of Measures to Enhance the Success of Global Climate Treaties*

We analyze important forces that hamper the formation of successful self-enforcing agreements to mitigate global warming. The analysis combines two modules: a) a computable general equilibrium model that captures the feedback between the economy, environmental damages and the climate system and b) a game theoretic model that determines stable coalitions in the presence of free-riding incentives. We consider two types of measures to enhance the success of international environmental treaty-making: a) transfers, aiming at balancing asymmetric gains from cooperation; b) institutional changes, aiming at making it more difficult to upset stability of a treaty. We find that institutional changes may be as important as transfers and should therefore receive more attention in future international negotiations.design of climate treaty protocol, coalition formation, non-cooperative game theory, integrated assessment model

New Roads to International Environmental Agreements: The Case of Global Warming

We analyze with an integrated assessment model of climate change the formation of international environmental agreements (IEAs) by applying the widely used concept of internal& external stability and several modifications of it. We relax the assumptions of a single agreement and open membership rule. It turns out that regional agreements are superior to a single agreement and exclusive is superior to open membership in welfare and ecological terms. Moreover, we show the importance of transfers for successful treaty-making. We relate our results to the design of current and past IEAs as well as to other issues of international policy coordination.design of climate treaty protocol, coalition formation, non-cooperative game theory

New Roads to International Environmental Agreements: The Case of Global Warming

We analyze with an integrated assessment model of climate change the formation of interna-tional environmental agreements (IEAs) by applying the widely used concept of inter-nal & external stability and several modifications of it. We relax the assumptions of a single agreement and open membership rule. It turns out that regional agreements are superior to a single agreement and exclusive is superior to open membership in welfare and ecological terms. Moreover, we show the importance of transfers for successful treaty-making. We relate our results to the design of current and past IEAs as well as to other issues of international policy coordination.Design of climate treaty protocol, Coalition formation, Non-cooperative game theory

Simulating a Sequential Coalition Formation Process for the Climate Change Problem: First Come, but Second Served?

We analyze stability of self-enforcing climate agreements based on a data set generated by the CLIMNEG world simulation model (CWSM), version 1.2. We consider two new aspects which appear important in actual treaty-making. First, we consider a sequential coalition formation process where players can make proposals which are either accepted or countered by other proposals. Second, we analyze whether a moderator, like an international organization, even without enforcement power, can improve upon globally suboptimal outcomes through coordinating actions by making recommendations that must be Pareto-improving to all parties. We discuss the conceptual difficulties of implementing our algorithm.International Climate Agreements, Sequential Coalition Formation, Coordination through Moderator, Integrated Assessment Model, Algorithm for Computations

Optimal Transfers and Participation Decisions in International Environmental Agreements

The literature on international environmental agreements has recognized the role transfers play in encouraging participation in international environmental agreements (IEAs), but the few results achieved so far are overly specific and do not exploit the full potential of transfers for successful treaty-making. Therefore, in this paper, we develop a framework that enables us to study the role of transfers in a more systematic way. We propose a design for transfers using both internal and external financial resources and making “welfare optimal agreements” self-enforcing. To illustrate the relevance of our transfer scheme for actual treaty-making, we use a well-known integrated assessment model of climate change to show how appropriate transfers may be able to induce almost all countries into signing a self-enforcing climate treaty.Self-enforcing international environmental agreements, Climate policy, Transfers

An Almost Ideal Sharing Scheme for Coalition Games with Externalities

Cooperative agreements among firms to coordinate R&D investments and share knowledge or coordination among nations to reduce trade barriers or to provide global public goods usually proves difficult due to free-rider incentives. In this paper, we propose a sharing scheme for the distribution of the gains from cooperation for games with externalities and heterogeneous players in order to mitigate free-rider problems. We show that every sharing rule belonging to our scheme leads to the same set of stable coalitions which is never empty. This scheme is “almost ideal” because it stabilizes those coalitions generating the highest possible global worth among the set of all “potentially stable coalitions”. Our Almost Ideal Sharing Scheme is particularly powerful for economic problems where outsiders benefit from the coalition’s actions (positive externalities) and which therefore are likely to suffer from severe free-riding

Simulating a Sequential Coalition Formation Process for the Climate Change Problem: First Come, but Second Served?

We analyze stability of self-enforcing climate agreements based on a data set generated by the CLIMNEG world simulation model (CWSM), version 1.2. We consider two new aspects which appear important in actual treaty-making. First, we consider a sequential coalition formation process where players can make proposals which are either accepted or countered by other proposals. Second, we analyze whether a moderator, like an international organization, even without enforcement power, can improve upon globally suboptimal outcomes through coordinating actions by making recommendations that must be Pareto-improving to all parties. We discuss the conceptual difficulties of implementing our algorithm