Sllly but alarming: the energy cost of bitcoin operations is on the rise and Bitcoins are consuming an incredibly large amount of energy. Due to the amount of computer power required, right now each Bitcoin transaction consumes 228 kwh (kilowatt hour), which equals the monthly consumption of a houselhold in a developed country. Each. Single. Transaction.
The global equivalent are some 24 twh (terawatt hour) per year, which is roughly the same energy as is consumed by Nigeria.
Using as model a mining facility powered by a coal plant, each new bitcoin mined is causing the emission of between 22 and 40 tons of CO2 (depending on the cost of cooling the farms and the hash/energy proficency of the farm boards).
And all this will just become worse and worse as more bitcoins are mined and traded.