A Non-cooperative Foundation of Core-Stability in Positive Externality NTU-Coalition Games

We identify the core as an appealing stability concept of cooperative game theory, but argue that the non-cooperative approach has conceptual advantages in the context of economic problems with externalities. Therefore, we derive a non-cooperative foundation of core-stability for positive externality NTU-games. First, in the spirit of Hart/Kurz (1983), we develop a game that we call ?-game and show that strong Nash equilibria coalition structures in this game are identical to ?- and ?-core stable coalition structures. Second, as a by-product of the definition of the ?-game, we develop an extension called an ?-game. Finally, we compare equilibria in the ?- and ?-game with those in the ?- and ?-game of Hart and Kurz (1983).Core-stability, non-cooperative game theory, positive externality games

How the Rules of Coalition Formation Affect Stability of International Environmental Agreements

This paper compares stability of international environmental agreements for six different rules of coalition formation under very general conditions (any type of heterogeneity between countries). The rules can be interpreted as different institutional settings in which treaty formations take place and/or different designs of agreements. We consider open and restricted open membership game as well as four exclusive membership games with different degrees of unanimity required to form coalitions. From a policy perspective, counterintuitively, it turns out that stability is higher under exclusive than under open membership and stability increases with the degree of unanimity. We discuss the policy implications of our result for future treaty-making.Non-cooperative game theory, Rules of coalition formation, Stability

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

The incentives to participate in and the stability of international climate coalitions: a game theoretic approach using the WITCH Model

This paper uses WITCH, an integrated assessment model with a game-theoretic structure, to explore the prospects for, and the stability of broad coalitions to achieve ambitious climate change mitigation action. Only coalitions including all large emitting regions are found to be technically able to meet a concentration stabilisation target below 550 ppm CO2eq by 2100. Once the free-riding incentives of non-participants are taken into account, only a “grand coalition” including virtually all regions can be successful. This grand coalition is profitable as a whole, implying that all countries can gain from participation provided appropriate transfers are made across them. However, neither the grand coalition nor smaller but still environmentally significant coalitions appear to be stable. This is because the collective welfare surplus from cooperation is not found to be large enough for transfers to offset the free-riding incentives of all countries simultaneously. Some factors omitted from the analysis, which might improve coalition stability, include the co-benefits from mitigation action, the costless removal of fossil fuel subsidies, as well as alternative assumptions regarding countries’ bargaining behaviour.Climate policy; Climate coalition; Game theory; Free riding.

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

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 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

Stable Partitions in a Model with Group-Dependent Feasible Sets.

In this paper we consider a model of group formation where group of individuals may have different feasible sets. We focus on two polar cases, increasing returns, when the set of feasible alternatives increases if a new member joins thegroup, and decreasing returns, when a new member has an opposite effect and reduces the number of alternatives available for the enlarged group. We consider two notions, stability and strong stability of group structures, that correspond to Nash and Strong Nash equilibrium of the associated non-cooperative game. We prove existence results for various classes of environments and also investigate the link between the dimensionality of the set of alternatives and the existence of stable structures.feasible sets; stable partitions; positive externality; increasing and decreasing returns

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