Fight against global warming is a tough challenge requiring synergic efforts from governments, industry and scientific communities. Facing these challenges by means of sectorial or local approaches is a loosing strategy. A holistic approach is required to provide more flexibility and prompt responses to unpredicted side effects on environment, economy and society due to low carbon society policies. Furthermore coping with such complexity requires the adoption of decision support systems providing policy makers with possible scenarios and countermeasures. Precondition to them is to reach a common understanding on such domains as a formal specification. Ontologies are considered widely accepted means to share knowledge. They enable advanced semantic services to manage knowledge in a more effective and smart way. In this paper we address the European Emissions Trading System and we present the EREON ontology to represent knowledge on such domain. In particular we focus on contextual knowledge modeled as concepts and rules. Finally, we present the data acquisition and the data analysis services as applications of such ontology.