As nice as it would be, a not insignificant amount of coal being transported is destined to steel production. Steel is iron + carbon, and the easiest source of carbon is coal. Steel is pretty important, so that's not going away anytime soon. I wonder if carbon capture could make a product that could be used to replace coal here though, and fairly effectively sequester the carbon in an actually useful form?
What biomass grows the fastest without being waterlogged - I imagine bamboo or sugarcane or something
Grow that, and burn it to make carbon neutral steel; bonus points if you do it in a highrise/underground farm but frankly some medium term reversible environmental damage is preferable to killing off way more with climate change
Eh, purity is a thing. Biomass is the opposite of what you want there, but it could be doable.
I do wager, however, that the largest "climate cost" of steel comes from the repeated melting of the steel.
Still leagues ahead of biomass. Don't get me wrong, this is an issue that can be solved. Biomass can be converted to biogas which can be purified to produce methane (or you just burn biogas directly) which then in turn can be used for heat (or other purposes) - the problem here is the sheer amount of energy this requires. Yes, significant portions of the steel industry can be "decarbonised" (or at least I think so) but the effort is immense. Doable, necessary, but it will be a huge piece of work.
By "burn it" I meant turn it into charcoal... Charcoal averages 80% carbon (range 50-95%), whereas depending on the type coal ranges from 60-92% carbon, with the purest type, anthracite, being 86-92% carbon
Given a mass production system would likely result in more uniform carbon content near the top of the range, I don't think it's unreasonable to suggest that they could be swapped out pretty easily
Electric Arc Furnaces are probably our best bet for that - they're an established, proven technology and can be swapped over to a green power source without any other changes (assuming the society has the energy capacity). I think I remember reading that a factory somewhere in Europe had already done that but a quick search has failed me.
Certainly, they're the shit, but the energy capacity you mentioned is a huge issue. As I said in my other comment it should/could/has to be done, but it's anything but simple.