Energy efficiency and CO2 awareness are globally-important issues in cloud computing. With increasing attention being paid to the environmental impact of cloud computing there are concerns about the sustainability of cloud computing model as its uptake increases. In this respect, we consider it useful to provide a snapshot of the requirements for energy efficient and CO2 aware cloud computing to allow the conception and development of new techniques and approaches in this area. Further, we present a case study approach for energy efficient cloud sourcing that aims to build on these requirements.