  Green software engineering aims at reducing the environmental impact due to
developing, deploying, and managing software systems. Meanwhile, Cloud-IoT
paradigms can contribute to improving energy and carbon efficiency of
application deployments by (i) reducing the amount of data and the distance
they must travel across the network, (ii) by exploiting idle edge devices to
support application deployment. In this article, we propose a declarative
methodology and its Prolog prototype for determining placements of application
services onto Cloud-IoT infrastructures so to optimise energy and carbon
efficiency, also considering different infrastructure power sources and
operational costs. The proposal is assessed over a motivating example.
