The complex and uncertain nature of dealing with multi-modal transport emissions generates a need for appropriate methodology to support informed decision-making. This paper presents a System-of-Systems (SoS) approach that takes into account the complexity of a policy problem stemming from the interactions of multiple actors and technological artifacts. We discuss some SoS characteristics such as actor operational and managerial independency, the hierarchical and horizontal network of interdependencies among actors and artifacts, the emergent SoS behavior, and the presence of multiple sets of solutions for achieving an SoS objective. We illustrate such characteristics via the problem of assessing the carbon emission impact of on-demand air service (ODAS) and automobiles. Some preliminary results are presented regarding the impact of alternative fuels on carbon emissions.