In the years after signing the Paris agreement, corporations have been experiencing increasing pressure to monitor and reduce their carbon footprint. Nevertheless, the information and communication technology sector lacks an effective tool for monitoring and optimizing the carbon footprint of data transmissions over the public Internet.In this work, we propose a carbon-footprint transparency system based on a path-aware Internet architecture that enables endpoints to monitor the carbon footprint of their interdomain communications, and optimize it through carbonaware path selection. Furthermore, we show by means of simulations that in a realistic inter-domain topology, 85% of traffic sources could reduce the carbon footprint of their outbound inter-domain traffic by at least 50% through carbonaware path selection.