[cschwarm]

Burying biochar (the superset of charcoal, basically) in old coal mines or other geological structures is a feasible way for long-term storage. The carbon content can be up to 90%, depending on the method. Biochar can be made from nearly all forms of biomass as long as it's dry enought.

[antisemiotic]

Now I wonder how would old coal miners feel if you told them nowadays the coal is supposed to go in the ground.

[cschwarm]

I think, they would be happy to keep their jobs and get paid for several decades to come. Also, the coal companies wouldn't have to write off their investments, since some of their technology could probably be reused.