> You could calculate the rough CO2 emissions of a 1 BTC transaction by dividing annual estimated CO2 emissions by bitcoin miners (35 million tonnes) by the num

> You could calculate the rough CO2 emissions of a 1 BTC transaction by dividing annual estimated CO2 emissions by bitcoin miners (35 million tonnes) by the number of annual transactions (100 million) which equates to about 350kg of CO2. Even that would be misleading, because the number of transactions is a constant that has little bearing on the amount of work performed. Most of the revenue still comes from block reward, which disappears over time. Transactions fees would not support current levels of work. If anything the cost of creating a Bitcoin has a carbon footprint, but most Bitcoins haven't been created at current prices and difficulty levels. Given that creation of a Bitcoin is historically unique event that is certain to cease, it's not really worth losing sleep over in terms of CO2 emissions.