Purpose - The purpose of this paper is to focus on carbon accounting as one aspect of accounting for impacts on the environmental capital and to detail the "convergence" process between two emergent corporate carbon management accounting approaches within a multinational company. In contrast to the reporting stakeholder and regulatory focus, company-internal issues of carbon accounting have so far rarely been investigated in depth. Based on a qualitative analysis of this in-depth case study, questions about what could be considered an effective carbon management accounting system are raised. Design/methodology/approach - The research has been conducted with an in-depth case study, using participant observation (Spradley, 1980). The authors follow a pragmatic research approach, and the proposal of Malmi and Granlund (2009) "to create theories useful for practice is to solve practical problems with practitioners and synthesize the novel solutions to a more general form". Findings - This case study demonstrates that it is possible to connect two corporate carbon management accounting approaches focusing on products and the organization into a combined carbon management accounting system. This has potential impact in making carbon management accounting in organizations leaner, and more efficient in terms of performance measurement and external communication. Research limitations/implications - This research is based on a single case study, and more case studies in different industries could highlight further practical implementation difficulties and approaches to overcome.Practical implications - This paper unveils that different carbon management accounting approaches can emerge in parallel in the same corporation. The paper discusses possibilities and challenges to converge them in terms of methodology (emission factors for example) and/or in terms of information systems, on which the calculations are based.Originality/value - This is, to our knowledge, the first case study of an organization explicitly acknowledging the existence of multiple emerged carbon management accounting approaches and Case study on converging emergent approaches trying to make sense of them in a convergence process to create an overarching carbon accounting system.