Energy does not come from nothing. A large amount of it comes from polluting sources. In those cases there is a very direct relationship between the creation of energy and pollution.

Clean energy is obviously better, but suffers from a fundamental problem: energy is fungible.

If mining takes up 10 MWh of juice, anyone else who would have used that energy can’t. So they have to use other energy. Often fossil fuel based energy has to make up the difference. For all intents and purposes the mining used that fossil fuel energy.

If mining only used excess electricity produced by clean power plants, there would be no problem. But it’s not incentivized to use extra energy, it’s incentivized to use cheap energy. If energy can be generated by fossil fuels cheaper than what you can earn from mining, miners will use that energy. Producing pollution that wouldn’t have otherwise existed.

Even if mining only used spare energy generated from clean sources, using that energy means it can’t be stored to be used later, like at night. Possibly necessitating polluting generation later. (I know storage isn’t common today.)

If you can explain how mining either does or feasibly could given real incentives use only spare non-polluting energy I would love to know.