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That provoked me to do a Fermi estimate comparing banking's power consumption to Bitcoin's. Posting it in case anyone cares.
Estimated energy use of banking
The service sector uses 7% of global power and produces 68% of global GDP. Financial services make up about 17% of global GDP, hence about 25% of global services' contribution to GDP. If financial services have the same energy intensity as services in general, financial services use about 25% × 7% = 1.8% of global power. World energy consumption is of order 15 TW, so financial services use about 260 GW. Rounding that down semi-arbitrarily (because financial services include things like insurance & pension services, as well as banking), the relevant power consumption number might be something like 200 GW.
Estimated energy use of Bitcoin
A March blog post estimates that the Bitcoin network uses 0.774 GW to do 3250 petahashes per second. Scaling the power estimate up to the network's current hash rate (5000 petahashes/s, give or take) makes it 1.19 GW. So Bitcoin is a couple of orders of magnitude short of overtaking banking.
Of course, BTC is also many orders of magnitude short of banking in the volume of trusted transactions it enables - this is hardly an apples-to-apples comparison! A single BTC transaction is actually rather economically costly, and this will only become more fully apparent to BTC users over time, as the current block-creation subsidy keeps dwindling further.
Now don't get me wrong, BTC and other crypto-currencies are still interesting as a heroic effort to establish decentralized ... (read more)