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The Kyoto Protocol contains four cooperative implementation (CI) mechanisms: joint fulfillment (Article 4), joint implementation (Article 6), the Clean Development Mechanism (Article 12), and international emissions trading (Article 17). The common feature of these mechanisms is that they allow for the transfer of greenhouse gas (GHG) emissions allowances between Parties to the Protocol.
The question of which Party to a transfer—the buyer or the seller—is responsible if the seller exceeds its emission target is one of the most important issues to be resolved in the design and implementation of CI. The green/yellow/red symbols of a traffic light serve as a basic model for describing one approach to allocating responsibility. The traffic light approach is derived from the provisions of Article 6 of the Protocol, particularly paragraph 6.4. It is argued in this paper that the traffic light approach is not only applicable to Article 6 JI, but is an effective model for several of the other CI mechanisms as well.