I just don't understand how bitcoin mining will be sustainable too much longer with the rate of increase of electricity consumption and hardware requirements.

Mining profitability is a function of the price of the underlying asset.

Tank prices - by limiting fiat inroads for example - and you significantly limit mining activity.

The scale of waste (of electricity, human effort, hardware) dedicated to cryptocurrencies is staggering.

it's not a waste if somebody was willing to pay for it.

this statement is extremely subjective

exactly - the concept of waste is subjective. If you are arguing that energy production has way too many externalities not being accounted for, then i would agree. But that's not "waste" - that's bad regulation and pricing.

A globally enforced carbon tax will fix that problem, and allow the market price to reflect the costs completely. Then, if people wish to spend/invest their wealth on mining, let 'em. It's not a "waste", not any more than watching a theater production is a "waste".

The increase basically goes at the rate at which miners can afford. If they are all no longer able to pay for increasing power and hardware use, the hardware and power use will stop increasing,

This shouldn’t impact the network much, aiui.

That being said, the quantity of energy use is, I think, unfortunate.

If there were a carbon tax (paying to remove any CO2 emissions one contributes), which was universally enforced, then that would be enough for it to not concern me though.

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.

I was thinking just a consensus among countries to individually enforce it (and possibly economic sanctions on those that don’t, but maybe not).

And I was kind of speaking hypothetically? Not saying it was an achievable goal. Just saying that if it did happen, then there would be little to no reason to be concerned about the energy use.

Mining creates no wealth, just like printing money doesn't. It just accumulates it.

Bitcoin just won't be running all the transactions, it'll be a storage of wealth.

How is anybody ruining a market? If you want goods you compete in the market. If a miner is more motivated than Rusty the Rustacean to pay up for a laptop, that’s the end of the story.