A. Carbon Usage Effectiveness (CUE) (Green Grid and Energy Star)
The relatively new Carbon Usage Effectiveness (CUE) metric is very useful. It is a metric of the GHG emissions associated with a specific data center. This is emerging as an extremely important factor in the design, location, and operation of these facilities today and in the future. CUE was developed by the Green Grid. CUE, combined with the Power Usage Effectiveness (PUE, see below) metric enables data center operators to quickly assess the relative efficiency and sustainability of their data centers.
The GHG emissions from data energy consumption are calculated by multiplying the data center’s electricity use total by the GHG emission factor of the electric utility provider or regional electricity grid system. The CUE’s ideal value is zero (a zero carbon data center); CUE does not have a theoretical upper bound. Both CUE and PUE simply cover the operations of the data center. They do not cover the full environmental burden of the life-cycle of the data center and ICT equipment. For now, CUE is specifically limited to GHG Scope 1 and Scope 2 emissions.
B. GHG intensity of information (e.g. CO2e/TB of information)
This metric is similar to a GHG LCA result for certain ICT services; the difference is that the metric only covers the GHG emissions from the data center operations. It excludes emissions from manufacturing data center hardware. It requires the vendor to know the total energy usage, emission factors of the energy sources, and the total amount of information processed and delivered to customers. In an informational phone call CenturyLink indicated that they are currently calculating CO2/terabyte (TB) of information at the request of several customers, suggesting that this would be a reasonable metric for state purchasers to request as well.
Other applicable denominators are length of service (e.g. 5 minute phone call between two parties, or 30 minute webinar with 10 participants, etc.) or per application run (e.g. one database search). The appropriateness of different calculation denominators will depend on the type of ICT service procured. There is currently no “gold standard” for calculating this metric.