Companies are continuously being pressured by governments, customers and NGOs to become environmentally sustainable. In the process industries this is a very important problem since the environmental impacts are often very significant. Although the assessment of the environmental performance of supply chains is becoming a common practice, this topic still remains very challenging for various reasons. One of them is complexity. Supply chains are complex systems, involving several entities, flows, and actors with frequently opposing views and goals. Analysing such system requires the use of powerful tools, such as quantitative models, capable of handling the various logistics variables and contributing to the understanding of their interactions and trade-offs. Such complexity often results in a simplification of several aspects of the environmental analysis, being one the life cycle scope definition. In this work, we address this issue and through the use of a mixed integer linear model we study the extent to which life cycle scope definition influences managerial decisions in the design and planning of complex supply chains. A real case-study in the pulp and paper industry is explored.