This paper shows that if countries are farsighted when deciding whether to defect from a coalition, then the implementation of cleaner technologies, as embodied by a reduction in the emission per output ratio, may either improve or jeopardize the chances of reaching an international environmental agreement. A small change in the emission per output ratio can result in a discrete jump in the stable size of a coalition and global welfare evaluated under the stable coalition size. In the case of three countries, the grand coalition may be destabilized by the implementation of cleaner technologies, ultimately resulting in higher global emissions and lower global welfare. In the case of more than three countries, implementing cleaner technologies may result in a discrete jump, either upward or downward, of the largest stable coalition size and welfare. We examine both, the case of a flow and a stock pollutant. In the latter case, we show that the higher the stock of pollution at the instant when the cleaner technology is implemented, the more likely that a grand coalition of three countries is destabilized. Measures that enhance the natural rate of decay of stock pollutants are shown to have similar effects on the size of stable coalitions to reductions in the emission per output ratio. This article is protected by copyright. All rights reserved.