  Cloud computing has become the de facto paradigm for delivering software to
system users, with organizations and enterprises of all sizes making use of
cloud services in some way. On the surface, adopting the cloud appears to be a
very efficient approach for offloading concerns such as infrastructure
management, logistics, and most importantly for this work, energy consumption
and consequent carbon emissions to the cloud service provider. However, this is
in many ways not an appropriately accountable solution to managing the
contribution of the ICT sector to global emissions. To this effect, in this
paper we report on an exploratory case study done in collaboration with a
Software as a Service provider operating globally in the telecommunications
sector. The study reckons with the service provider using multi-tenant, that
is, shared, off-premises data centers for hosting their private cloud
infrastructure towards developing a fair model of allocating operational
emissions among the service tenants -- customer companies with many distinct
users.
  The developed emissions model has to account for allocating in an appropriate
manner the generated emissions between the tenants of the software provider
services, and among the different tenants of the same data center. A carbon
footprint report generator is developed building on the proposed model which
is, in turn, used to present sustainability reports to involved stakeholders
for evaluation purposes. Our results show that the model is perceived as
transparent, informative, and fair, with requested improvements focusing mainly
on the generated reports and the information contained therein.
