It's completely meaningless because GWh aren't interchangeable. A hydro o thermal energy source too far from inhabited places could be used for bitcoin mining and its CO2 footprint would be near zero.

I'm not saying you are wrong but this requires a far more exhaustive analysis.

There are transmission losses, but they're not that great.

Please point out which power plants were built especially for proof of work mining. The others were apparently built with something else in mind and their power is now being wasted on western people's get-rich-quick schemes.

So we'd build energy production away from where people live just to mine a digital currency?

The government's of the world seem concerningly content underplaying this.

I'm glad I don't have kids.

If all crypto was mined with renewable energy, would it be a huge environmental issue?

Yes. Renewable doesn't mean without a carbon or other cost. All energy usage and production takes resources from the planet.

Yes. Even if every major country on earth requires PoW systems to use renewable electricity (which won't happen any time soon in the first place) and can't run on the regular mixed grid, then after switching to countries without such laws (until there are none left), the renewable energy will be bought up at the source and the coal and gas plants will continue to supply everyone else. Nothing changes.

We need to change everything else to renewable before this really starts to be effective.

It would make a much bigger impact if some countries, where users want to use cryptocurrency, make it illegal to use proof-of-work-based goods or currencies (whatever it's classified as). Suddenly a coin with PoS or something else becomes much more popular and we might, perhaps, shift over to a digital coin that is not a climate disaster.