Technical systems are increasingly complex and interconnected, forming higher level System of Systems (SoS). SoS provide emergent functions which are greater or different than the sum of the functions of their constituent systems. To be able to assess the environmental impact of an SoS, a functional unit is required. Therefore, we discuss the opportunities of synthetic emergence to serve as functional unit of SoS. A deep understanding of emergent properties and the function of SoS is given. Finally, a comprehensive discussion uses the cases of smart energy grids and urban symbiotic food production systems for initial reflections about the concept.