In this paper a decision support system for systematically evaluating the impact of labeling products with their carbon footprints is developed and applied to prioritize products for carbon labeling in a large supermarket chain in the UK. Carbon labels may change consumers' behavior and encourage suppliers to implement carbon-reduction solutions. Those changes may, however, lead to unintended risks. To handle the challenges of uncertainties in the evaluation, the Evidential Reasoning approach and the Intelligent Decision System software for multi-criteria decision analysis are applied to support the process. The system developed can be applied to assessing the impact of sustainable development policies to maximize their benefits and minimize their risks.