Instructors may be reluctant to adopt simulations because of time, labor, or material constraints, or perceived incompatibility with large classes. In fact, simple games can cover multiple key concepts with minimal time and effort by the instructor. Simple games are also adaptable to other topics and classes, including large lectures. This article presents a simulation in which students negotiate a global greenhouse gas reduction agreement. Three scenarios model basic climate change mitigation, follow-on agreements for climate stabilization, and the surprise withdrawal of signatories after a domestic leadership turnover (e.g., the 2016 U.S. presidential election). The simulation teaches key concepts such as anarchy, collective action, preference divergence, and commitment problems. Concepts such as institutions, identity, and levels of analysis arise organically from game play. The exercise has extremely low cost and setup time. It can be run in 15 minutes or extended for a full class period. The game may also be repurposed to simulate other bargaining or collective action issues. This case study shows that simulations can be efficient and adaptable. Instructors can create their own simple games to enhance comprehension of key concepts.