In life cycle assessments, material and energy flows are used to produce the life cycle inventory. The carbon footprint simplifies the life cycle assessment by referring to a single result factor. However, some parallels with cost accounting then become distinctly apparent, for instance the emission factors of raw materials or other preliminary inputs can be understood as "prices". Known cost-accounting methods can then be used for calculation and evaluation, enabling aspects such as joint processes, recycling processes, closed loop management or allocations to be solved elegantly. Challenges connected with the carbon footprint include how to handle carbon storage and carbon dioxide of biogenic origin, as well as how to consider changes in land use. The article points up how, by applying a stringent methodology, such issues can be treated in material and energy flow analyses.