The highest estimates for Bitcoins annual terawatt hours consumption is 28.67. This means, more than 3 times more efficient than a very conservative calculation of the cost of the global banking system.

Carlos Domingo: The Bitcoin vs Visa Electricity Consumption Fallacy https://hackernoon.com/the-bitcoin-vs-visa-electricity-consumption-fallacy-8cf194987a50

Jonathan Koomey gets quoted in the Washington Post, and other estimates https://www.washingtonpost.com/news/energy-environment/wp/2017/12/19/why-the-bitcoin-craze-is-using-up-so-much-energy

Highest estimates by Digiconomist https://digiconomist.net/bitcoin-energy-consumption

Data center energy consumption study from 2014, estimated 10% https://ftalphaville.ft.com/2014/09/09/1960891/the-dark-side-of-data-centres

What’s the carbon footprint of your credit card? https://www.creditcards.com/credit-card-news/carbon-footprint-credit-card-1276.php

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Carlos Domingo estimated banks electricity consumption.

Estimates for how many banks are in the world range from around 14600 to 25000, or even more than 60000. In this comparison (30,000 banks) I will just include three values: server costs, branches costs and ATM costs. Of course, banks (and its employees), consume a lot more electricity from other sources.

How many servers is each bank using to run their banking infrastructure? To pick a very conservative number, on average 100 servers per bank, for banking infrastructure, internal operations, accounting systems, website. If a server in average consumes 400Wh and since it always on, this means that banks consume in total 800 Megawatt hours.

Now we calculate the electricity consumption of bank branches. According to the World Bank there are 12.5 branches per 100,000 adults in the world so if the world population is 7.6 billion people and we have around 70% adults, this means a total of 665000 branches.

Calculating branch consumption is more tricky since there are lots of things to take into account like size of the branch or number of employees as well as several things consuming electricity like lights, cooling, computers, monitors, etc. And they are not open all the time, for a conservative number 10 kilowatt hours per branch assuming an average branch has 10 light bulbs,

two air conditioning units that only run 20% of the time and 12 desktop computers running an average of 12 hours a day, 20 days a month through the year.

There were about 3 million ATMs worldwide in 2015. For small bank ATM machines, the average daily power consumption comes around 5 Watt hours. So total consumption for banks during a year for all those three metrics is around 26 terawatt hours on servers, 58 terawatt hours on branches and 13 terawatt hours on ATMs, for a total of close to a 100 terawatt hours a year.

The highest estimates for Bitcoins annual terawatt hours consumption is 28.67. This means, more than 3 times more efficient than a very conservative calculation of the cost of the global banking system.

And then we need to factor in the energy consumption of card readers and credit cards, data centers to make transactions. One 2014 study estimated that data centers consume 10% of the global energy consumption alone. Hence, there are a lot more variables to consider when comparing cryptocurrency with other forms of financial transactions, and also the fact that many bitcoin miners use renewable energy.

You need to divide the total consumption vs number of transactions done. And I am pretty sure that the total number of transactions that the whole banking system does every year is many orders of magnitude bigger than the number of transactions in bitcoin.