A proper CO2 tax wouldn't be disruptive to bitcoin, bitcoin only cares that everyone pays the same price for electricity. If the absolute cost of electricity goes up, nothing changes.
That said, not every cryptocurrency is reliant upon brute forcing hashing algorithms to verify.
We don't make seatbelts out of titanium 8 inches thick with their own airbags when they're mounted in a go-kart.
When the hash rate dropped what, 75%, off the back of the China exodus literally nothing happened.
tl;dr: Same transaction throughput, same security, just less efficient.
The cost of electricity does impact the cost per transaction on the network, does it not?
The only thing that impacts transaction costs is how many other people are trying to clear their own transactions and bidding up the sat/vbyte rate.
TotalCost = DirectCost + ProportionalAllocationOfBlockReward
So yes, the transaction cost does scale with consumption of resources, albeit in a tail-wagging-the-dog kind of way, because the price of the block reward changes with price allowing more resources to be consumed.
Currently the actual cost of a Bitcoin transaction is $2.44 in direct costs + (6.25 * 41000)/2750 = $93 in indirect costs, so right around $95.44 - and that's using I believe the maximum possible transactions per block, the reality is it's more expensive still.
Move over Bank of America, there's a new king in town.
ESG people are trying to solve something that is already solved. POW is here to stay and will scale tremendously well as we all move to layer 2.
You completely synthesized $93/1000000 obviously, and as we discussed it would take 75 years to open a channel for everyone alive today and $300,000,000,000.
More mining → higher difficulty → higher electricity usage per block.
The transaction costs paid are independent of difficulty or number of miners. Transaction cost depends on the demand. A block has a limited size in bytes. If more people want to send transactions than there is room in the current block, the miner that mines that block will include the transactions that include the highest fee.
When sending a transaction, you can choose that fee. Higher fee → higher chance of being included. Bitcoin clients will usually calculate a reasonable fee for you, based on the demand.
So its scenario #2 in your comment.
As long as there is free space in the blocks, average transaction fees will remain low. If there are a lot of transactions in the mempool waiting to be included in a block, users will need to submit transactions with higher related fees to ensure they get picked to be included in a block soon.
Remember, miners don't necessarily set transaction fees. Users choose what they're willing to pay for their transactions, essentially placing a bid. Miners choose the transactions that maximize the fees per block. Miners always want as full of blocks as possible because there will only be a block roughly every 10 minutes.