Recently, Facebook provided us some information on their server park. They use about 30000 servers, and not surprisingly, most of them are running the PHP code to generate pages full of social info for their users.
We do not yet know what the outcome (if any!) of Kopenhagen will be, but what do these 30000 servers mean in terms of CO2? And what would be the impact of a more sane language instead of PHP?
Since an average server consumes about 200 Watt , and with an average SI EER (Site Infrastructure Energy Efficiency Ratio) of 2  this translates to around 400 Watt including cooling and other overhead. In the USA, an average of 560 grams CO2 is emitted per generated Killo Watt hour , and this brings us to a total CO2 emission by the Facebook server park of about 59 000 ton of CO2 per year.
To put this number in perspective: The entire CO2 emission of the USA is 5 752 289 000 ton of CO2 per year and 66 693 000 ton for Finland . So, this server park emits an amount of CO2 that is about 1/1000 of the total of CO2 emissions by Finland. I would argue that is not quite negligible.
As they only say that "the bulk" is running PHP (edit: for those of you to lazy to read about the Facebook architecture , that is solely Apache/PHP, no database, no memcache, and to quote Jeff Rotschild of Facebook: “the need for those is a function of the runtime efficiency issues of PHP” ), let’s assume this to be 25 000 of the 30 000 (edit: and this would be in line with other bits of info that they run around 800 dedicated memcached servers and a few thousand database servers). If C++ would have been used instead of PHP, then 22 500 servers could be powered down (assuming a conservative ratio of 10 for the efficiency of C++ versus PHP code ), or a reduction of 49 000 ton.
Of course, it is a bit unfair to isolate Facebook here. Their servers are only a tiny fraction of computers deployed world-wide that are interpreting PHP code.
But I think it is fair to say that using PHP, especially for large deployments, is not very Kopenhagen.
For what it’s all worth.