So it is relatively difficult to get exact data and all we can really get from the information supplied is electricity usage. That, plus the mix of electricity

So it is relatively difficult to get exact data and all we can really get from the information supplied is electricity usage. That, plus the mix of electricity in the Data Centre location gives an approximation (again, it's an educated guess) of carbon emissions related to a site. Efficiencies are actually an irrelevance due to the rapid increase in usage swallowing up any gains caused by efficiencies. Oh and the 2% from Data Centres is a conservative estimate. It's probably higher. We simply don't have the data because it's not required to share it.