I do have a pathological aversion to the ridiculous quantity of energy that some crypto systems demand.
It has to be like that, by design. There must be ridiculous quantities of power used, or disk space, or expensive hardware, or some other difficult-to-obtain commodity.
Why? Firstly, it is because the coins themselves are a value store. They are something you can prove ownership of, and you can transfer that ownership in exchange for goods and services. Without a central issuing authority it must be difficult to bring new ones into existence - otherwise there would be an infinite supply and they would all be worthless.
Secondly, the decentralized ledger requires consensus between a group of anonymous parties - in effect, they are voting between themselves to agree how the ledger proceeds. If it were easy to gain votes, and any one party could throw enough resources at it to get >50% of voting rights, they could make any transaction they wanted (such as, transferring all assets to themselves). Hence this part must be very hard as well.
Now, you are quite right: there are other ways of doing this which would use far less energy.
To start with, some central authority could issue unique tokens. They could be as simple as a serial number with a digital signature. Very easy. This authority would control the supply and who it gives or loans them to.
Then if user A agrees to transfer their token to transfer B, the document recording this transfer could also be notarised by some central authority (not necessarily the same one). Just add a transaction timestamp or serial number and a digital signature - job done.
Notice that this central authority would also be able to reverse transactions or confiscate funds, since they are able to sign any transfer - including ones they create themselves.
But what you've just invented is regular fiat money, with a central issuer (e.g. Bank of England) and the banks which interact with it.
Visa and Mastercard transactions are cheap, precisely because they are making single-source-of-truth digital records of regular money transactions, with no need for distributed consensus, and using money that already exists.
Biting the hand that feeds IT
