My full node at home used about 50 Watts.  By comparison to a centrally heated bank branch with several staff who drive to work, quite a big energy saving, and I don't have to go there to stand around in a queue.  The blockchain itself, although it does admitedly use far more energy that we would like it to, could be compared to the entire finance sector plus services plus outsourced services such as workplace anti-fraud and employee retention bonus.  It is centuries of overpaid loyal employees who created trustworthy conventional currency, so how much CO2 had those cost ?

The office light bulb in a major Wall Street finance institution is the wrong CO2e to compare to Bitcoin, and they might have paid some third world charlie to offset their carbon emissions from that light bulb.  The other CO2 caused by all things bought with all of the gross salaries plus bonuses plus construction plus other spending by those institutions all causes concrete to be bought, precious things for someone to be bought, all causing CO2e.  There is a big cost of loyal employees.

Using 2018 figures, as this years' are incomplete, US GDP was about 20.5 $TN (20.5 x10^12 US$).  US CO2 was about 5 GT (5 x10^9 Metric Tons; 16 Tons per capita per annum before imports).  So for every $4100 issued in the US, on average 1 Metric Ton (1000kg) of CO2 blows out in the USA (not counting other CO2 elsewhere needed to make components and imports). 

Now how does the CO2e of all the money creation by conventional $ finance in three decades compare to the CO2e of all the 21M Bitcoins which will ever be made ?  Are there other harms caused by creation of conventional $ ?