The increasing utilization of cloud resources raises several issues related to their environmental impact and, more in general, sustainability. Recently, most of the contributions have focused on energy efficiency achieved through a better physical and virtual resource management. The present paper considers instead the application level, extending the focus to the reduction of CO 2 emissions related to the execution of applications. We aim to exploit adaptivity through the design of an Application Controller that, enacting the right adaptation strategy for a given context, allows the improvement of the trade off between QoS and CO 2 emission reduction. The effectiveness of the approach has been shown running an HPC application in a federated cloud infrastructure.