>but that amount is substantially less than the energy it costs to keep no fewer than three Fortune 500 financial companies running at full steam for a few days.

Ridiculous comparison. They are working on other transactions as well. Currently a bitcoin transaction uses 427kWh.

One thing that is interesting to think about is that once block rewards go away, increasing the transaction capacity of the chain will probably lower energy usage. Competition on transaction fees will dry up if more transactions can fit on the chain per minute, reducing the total reward from fees and making mining unprofitable until total network electricity costs go down (by miners shutting down) until equilibrium is reached again.

But txn fees are still only 15% of the total block reward so those effects won't really matter for a while. If satoshi had predicted this rise in value, he would have made the block rewards drop faster than once every 4 years. Secure network consensus is not what the mining market is getting paid by, it's getting paid by the $140k USD created out of thin air every 10 minutes.

Regarding the proof-of-stake part: Ethereum devs are also working on sharding which will make scaling on the Ethereum Blockchain way easier. I really think that Ethereum will be the No.1 cryptocurrency in the near future. Bitcoin devs showed plenty of times, that they are not capable of keeping pace with demand (couldn't even get the block size thing right). Bitcoin is virtually dead. No one can really use it for real world transactions. Plus Bitcoin in reality is a really central coin, completely in the hands of the miners. Even if the Bitcoin devs decided to go with PoS, the miners wouldn't agree.

> But electricity costs matter even more to a Bitcoin miner than typical heavy industry. Electricity costs can be 30-70% of their total costs of operation.

> [...] If Bitcoin mining really does begin to consume vast quantities of the global electricity supply it will, it follows, spur massive growth in efficient electricity production—i.e. the green energy revolution. Moore’s Law was partially a story about incredible advances in materials science, but it was also a story about incredible demand for computing that drove those advances and made semiconductor research and development profitable. If you want to see a Moore’s-Law-like revolution in energy, then you should be rooting for, and not against, Bitcoin. The fact is that the Bitcoin network, right now, is providing a $200,000 bounty every 10 minutes (the mining reward) to the person who can find the cheapest energy on the planet.

Bitcoin's energy use will tend to raise to match the mining profits. As long as both BTC's price and transaction fees keep raising, the energy miners spend will continue to raise. BTC's price is going up due to speculation, and transaction fees due to blocks being full.