Global steelmaking is responsible for about 7-9% of global CO₂ emissions (IEA data), a share comparable to cement and greater than the entire civil aviation sector. The reason is chemical, not engineering: the traditional process for producing steel from iron ore requires stripping oxygen from iron oxides (Fe₂O₃, Fe₃O₄) through a carbothermic reduction reaction — the carbon in coke bonds with the oxygen to form CO₂, while metallic iron is released. There's no way to avoid that CO₂ as long as the reducing agent is fossil carbon: it's a direct consequence of the reaction's thermodynamics, not a flaw that can be fixed with better plant efficiency.
Blast furnace-converter: the dominant route, the most emissive
The still-dominant global production route (BF-BOF, Blast Furnace - Basic Oxygen Furnace) starts from iron ore and metallurgical coke, melts them in the blast furnace at about 1,500°C, and refines the raw iron (pig iron) by removing excess carbon in an oxygen converter. The process emits about 1.8-2.3 kg of CO₂ per kg of steel produced, and its energy intensity makes it hard to electrify directly: coke isn't just fuel, it's the chemical reducing agent itself. Swapping in renewable electricity for the fossil fuel isn't enough — coke has to be replaced with a different chemical reductant altogether.
Electric arc furnace: recycling, not reduction
The already industrially mature alternative route is the electric arc furnace (EAF), which doesn't reduce iron ore but melts existing steel scrap using a high-power electric arc. With no carbothermic reduction reaction to carry out, direct emissions drop to about 0.3-0.5 kg of CO₂ per kg of steel — a quarter of the blast furnace's — and drop further still if the electricity used comes from renewable sources. The EAF's limit isn't technical but a matter of raw-material availability: you can only produce as much steel as there is scrap available on the market, which is why the EAF alone can't fully replace primary production from ore — new "virgin" iron is still needed to cover the growth in global demand that recycling alone doesn't meet.
DRI and green hydrogen: replacing coke with hydrogen
The most promising technology for a radical cut is Direct Reduced Iron (DRI), in which iron ore is reduced not with coke but with a reducing gas — initially natural gas (methane), which still emits CO₂ but less than coke; in its most advanced version, pure hydrogen. When hydrogen reacts with iron oxide, the byproduct isn't CO₂ but simple water vapor (H₂O) — if the hydrogen itself is produced by electrolysis from renewable electricity ("green hydrogen"), the whole process approaches near-zero emissions. The Swedish consortium HYBRIT (SSAB, LKAB, Vattenfall) produced the first tonnes of fossil-free steel with this process in 2021, and the H2 Green Steel project is building the first industrial-scale plant in Sweden. The challenge is no longer proving the process works — it's scaling it: it needs enormous quantities of green hydrogen and dedicated renewable electricity, and costs today remain significantly higher than the traditional route.
The role of policy: Europe's CBAM
None of these technologies will spread on an industrial scale purely on market convenience in the short term, because "green" steel currently costs more than traditional steel. That's why the European Union has introduced the Carbon Border Adjustment Mechanism (CBAM), which from 2026 applies a levy on steel imported from outside the EU proportional to the carbon embedded in its production — an indirect but powerful incentive to make decarbonized European steel competitive with steel produced through more emissive processes elsewhere. This is the kind of regulatory intervention that, more than technological innovation alone, will determine the real speed of the transition over the next decade.