[dTal]

If you have enough green energy to unburn CO2, why not just... use that energy directly? Digging up carbon, burning it, and polluting it, only to spend the effort to capture it, unburn it, and rebury it would be absurd and inefficient.

That being said, I believe carbon capture proposals don't typically involve unburning the carbon - just capturing it and storing it. So the energy situation isn't as bad as your calculations.