Facebook provided information related to server size a month ago. They used about 30,000 servers, most of which ran PHP code to generate users' social homepages. Jumping into the climate change debate in Copenhagen: How much CO2 will these servers produce? How much CO2 emissions would be reduced if PHP code was replaced by another language?
A server has about 200 watts of power, and about 400 watts for cooling and other overhead. In the United States, an average of 560 grams of carbon dioxide is produced per kilowatt hour, and Facebook's servers produce a total of 59,000 tons of carbon dioxide per year. Assuming that there are about 25,000 servers running PHP code, if the PHP code is replaced by C++ code, based on the calculation that the efficiency of C++ code is 10 times that of PHP code, about 22,500 servers can be shut down, which will reduce 49,000 tons of carbon dioxide emissions. Of course, this is a bit unfair to Facebook. Their servers only account for a very small percentage of the total servers running PHP code in the world.