You're always going to have somewhere around the world with cheaper electricity and people with asics and as long as someone has these things, they will be processing a large amount of crypto transactions and generating loads of wealth. Another incentive: if a single entity has >50% of mining power, they have control of the blockchain.

The only way the miners quit using so much electricity is if the demand goes down (less transactions and less fees) and/or a new cryptocurrency that uses proof of work starts running the game. Proof of work reduces electricity use on the scale of 10000ths to millionths compared to Bitcoin.

Your carbon tax is absolute idiocy in a world where any countries can just give you the middle finger. Would it be universally enforced with a global army that goes and sacks anyone who doesn't follow the rules? Take a look at the UN and see how that works. Many smaller less wealthy countries shit on UN policies all the time and nobody bats an eye.