This paper describes the design and implementation of a mobile app, Smiling Earth, to support citizens to contribute to climate change by being aware of their carbon footprint and making changes in their daily energy consumption and transportation. One of the main aims of this work is to explore the ways in which ICT could help raise awareness and educate citizens about their actions and their consequences on the environment. The Smiling Earth app is designed to visualise data about citizens’ activities and to motivate citizens to change their behavior to reduce their CO2 emissions by changing their transportation habits. The app takes a broader perspective of CO2 emissions, bringing together the transport and energy sectors. The design process and a preliminary evaluation of Smiling Earth is presented in the paper. This work has been conducted as a part of the EU DESENT project.