As for the environmental impact: individual Bitcoin transactions don’t directly increase energy usage. Miners consume electricity regardless of whether any given person transacts. And while mining is energy intensive, it doesn't have an environmental impact in itself.
The context I was looking at related to storing data in the bitcoin ledger. I think I commented here, I'll have to look back and see.
When you send a transaction, you get to pick what fee you'd like to use. For this kind of service, transaction speed isn't really important so you can get away with setting a low fee.
Here's a 0.15$ fee transaction that was mined just 6 minutes ago: https://mempool.space/tx/2e66ba1758e233ff1b2395c7db55f8327de...
By "off-chain", I meant something like BuyMeACoffee letting users top up a wallet via an on-chain deposit, and then handling tips internally (e.g., in a SQL database). That way, small payments don't each require a blockchain transaction.
But in general, I agree that cryptocurrencies could help the problem, but it still carries the compliance and AML risks unless you can outsource that to a 3rd party. What happens if you accept funds from an OFAC or other sanctioned account? Violating AML can come with huge fines and is generally just a massive headache. Cash doesn't have these issues as the evidence is generally impossible to track well. With nearly all cryptocurrencies, the entire ledger is open, so if you accidentally accepted payment from the wrong person, you could get royally screwed at some later time.
The only thing that can change value is if the global hash rate significantly changes. This is why we have the difficulty readjustment every 2016 blocks (give or take 2 weeks).
The key is emissions, not energy use. If I have a process that benefits mankind (a global, decentralized, permissionless hard money that doesn't suffer from politics or unelected officials) and I am using 100% renewable energy, then there is no environmental cost.
Bitcoin mining is very cutt-throat. It is a bleeding-edge, hyper-competitive business of reducing margins. Because I only needs an energy connection, some HVAC and internet connectivity, miners are very mobile and can move from place to place after setting up shop somewhere. This means that they seek the absolute lowest energy cost (the difference of paying 1c more per kWh can be essential) means that they are the energy consumer of last resort. Hydrodams and other renewables often produce at moments that demand is lower, and having a bitcoin miner nearby that is willing to gobble up all your excess production means your solar farm or hydrodam suddenly makes a profit at most times of the day.
It also means that investors are more willing to invest in renewable energy in places where formerly, building this infrastructure was impossible. There is a village in Malawi, Afrika where building a hydro dam was possible, but not financially sensible. None of the villagers had electric appliances, so building the dam meant running it would not be profitable for a very long time. Now, you can just add a set of bitcoin miners and run the dam at 100% capacity until people start installing freezers, televisions, etc. This benefits the investors, the villagers, and the bitcoin ecosystem.
Bitcoin's environmental costs is a highly politicized complex puzzle that is hardly as negative as the mainstream media and anyone that hasn't researched it claims it is. It bothers me to no end.