[AgentME]

>A thought experiment: how much energy should Bitcoin use?

If it used proof-of-stake, then it should be a negligible amount compared to what it uses now.

(Disclaimer: proof-of-stake is still being researched. Many altcoins presently claiming to be proof-of-stake rely on centralization (peercoin), likely have issues, and/or are underverified. I'm cautiously optimistic about the Ethereum community's thorough research into proof-of-stake.)