Well, there's sequestration and then there's sequestration. I have a tendency to consider it sequestered only if it stays there on the geological time scale.

They've also been experimenting with mining CO2 from the atmosphere and turning it back into solids and into fuels. Or so I've heard. I bet even THOSE operations use less energy than Bitcoin mining, especially if they are solar powered.

At least they have a useful end product. Bitcoin mining does not.

But the really successful operations are using fossil fuel power plant output as their input. They get a lot more CO2 that way and it would just get dumped into the atmosphere otherwise. One of the problems is that it takes as much or more energy to turn waste CO2 into fuel as you get by burning the fuel to begin with. This is why "clean coal" is a bad joke. Second Law of Thermodynamics and all.

But it is a way you could make methane out of waste CO2 and solar energy, and feed the methane back into the natural gas system. Probably more efficient though just to feed the solar energy right into the electric grid.