The Uptime Institute has recently described the most usual metrics used in the data center industry to report on corporate sustainability.
Most of these metrics are interrelated, e.g., IT power consumption is a part of PUE, as well as directly related to Server Utilisation and Data Centre carbon emissions. But these interrelations seem to be less than well understood. Although it might look contradictory, an improvement in PUE (i.e., reducing it) might increase the IT power consumption and the overall carbon emissions. An increase in server utilisation will not always change PUE, but it will increase power consumption; as much as higher server utilization is an obvious efficiency target, no one should be led to believe that it will deliver less net carbon emissions.
Understanding these interrelations is just the first step.