[nnfy]

You simply cannot justify that first order approximation. There is no reason so believe that the financial industry takes power in proportion to it's relative size of GDP. In fact I would expect the financial industry to require a higher proportion of power to keep servers/ATMs/staff computers running.

[matthewowen]

this seems... unlikely, given that (eg) factories exist.

[TheDong]

Bitcoin's power use is proportional to its worth however.

If bitcoin has 300 trillion worth of transactoins, that means being able to mount a 51% attack on the network has a value in the trillions..

Therefore, if you're using less than trillions of dollars of energy to secure it, someone will mount an attack.

The more valuable the bitcoin network is, the more incentive there is to attack it and the more energy must be wasted.