Yet another reason to implement a Carbon Tax & Dividend [0] ASAP. There's certainly an argument that the intentional waste of Proof of Work is more efficient than the overhead of existing banks; but I suspect the whole crypto world would migrate to Proof of Stake if forced to pay for their externalities. As is it, they simply borrow against the planetary credit card (probably at a rate of ~100x interest), sticking future generations with the bill for their "innovation".
Actually not at all: the elegant design of the difficulty adjustment means that even if the price of electricity went up or down by 10x, the rate of new Bitcoin issuance would change only temporarily.
I haven't met any Bitcoiner who wouldn't want CO2 emissions to be heavily taxed.
The problem with proof of stake that it decreases the security of the system. There are many ways to trade security of Bitcoin for convenience and extra features (Ethereum is a great example), but so far it seems that the market chooses security.
[0] https://clcouncil.org/economists-statement/