  Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this note, we describe the
sources of the inefficiencies in such networks. First we quantify how much
Carbon footprint such networks generate. We also discuss how much more mobile
traffic is expected to increase so that this Carbon footprint will even
increase tremendously more. We then discuss specific sources of inefficiency
and potential sources of improvement at the physical layer as well as higher
layers of the communication protocol hierarchy. In particular, considering that
most of the energy inefficiency in wireless cellular networks is at the base
stations, we discuss multi-tier networks and point to the potential of
exploiting mobility patterns in order to use base station energy judiciously.
