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
⅔ may be overestimating, but yes, they're native to all of the Middle East and Africa, and most of Europe (outside of Scandinavia) and mainland Asia (outside of deserts, Siberia etc.)