[gwicks56]

Why would we not tax the source of the problem. ie dirty energy generation via a carbon tax? That would then incentivize all energy use to become greener, rather than ad-hoc singling out individual use cases? A decent carbon tax would eliminate most dirty proof of work mining, as electricity is the major cost

[DennisP]

We absolutely should, but it seems unlikely that we will anytime soon. And to reduce Bitcoin's emissions it would have to be a global tax, which seems even more unlikely. For most products, a country can tax imports when other countries don't have corresponding taxes, but that's not really possible with Bitcoin.