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.
Coal has a bunch of impurities compared to charcoal I thought?
And if the repeated melting is done by burning biomass/charcoal or with clean(er) energy then it’s not a huge issue
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.
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.