Why not bury waste biomass in abandoned coal mine tunnels? Return the carbon to where it came from in the first place. Instead of composting on the surface (which releases CO2), all that industrial agricultural waste - chaff, sawdust, corn stalks,potato peels, used cooking oil, etc - as well as PLASTICS - could all just be buried in existing tunnels, kilometers under the surface, or pumped down into fracking /oil wells along with or instead of the water. In a few decades (centuries?), the stuff will decompose anaerobically, and we'll have fresh "fossil" fuels to start the cycle over again if we like. In the meantime, we remove billions of tons of carbon from the surface. Anyone see any obvious problems with this approach?