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.
A comparison is enough to grasp the scale of the problem. A large blast furnace produces several million tonnes of pig iron a year and runs without interruption for fifteen or twenty years, until its internal lining is rebuilt. Shutting it down and rebuilding it costs hundreds of millions and is decided decades in advance. That is why decisions on decarbonising steel are concentrated at the moments when a plant reaches the end of its campaign: that is when a steelworks decides whether to reline the blast furnace for another twenty years or replace it with an electric furnace or a direct-reduction plant. In Italy the most debated case is Taranto, the largest integrated steelworks in Europe, for years at the centre of a difficult process of environmental clean-up and conversion.
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.
For a European designer there is a practical detail of great importance. Not all steel products come from the same process. In Europe long products, that is I-beams, sections and reinforcing bars, are largely made in electric furnaces from scrap, and so already have a carbon footprint well below the world average. Flat products, that is plates, strip and coils from which profiled decking, light sections and cladding are made, come instead largely from blast furnaces, because they require steel with very few impurities, which is difficult to obtain from scrap. The same quantity of steel in a building can therefore have very different footprints depending on how it is split between sections and sheet, and where they were made.
The electric arc furnace is not a recent technology. The first was developed by the Frenchman Paul Héroult around 1900, and for decades it was used mainly for special steels. In Italy it has a particular history: after the war, around Brescia, dozens of small electric steelworks sprang up, the so-called "tondinari", which melted scrap to produce reinforcing bars for reconstruction and the building boom. They were small, flexible plants close to their markets, and helped make Italy one of the European countries with the highest share of electric-furnace steel. It is a tradition that today, with the need to cut emissions, is proving a competitive advantage.
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 company founded as H2 Green Steel, now Stegra, is building at Boden, in northern Sweden, one of the first industrial-scale plants based on this process. 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.
Hydrogen direct reduction, however, has two constraints that are discussed less often. The first is energy: producing by electrolysis the hydrogen needed for one tonne of steel, and then melting the reduced iron in an electric furnace, requires electricity in the order of several megawatt-hours. A steelworks of a few million tonnes a year therefore needs an amount of renewable energy comparable to the consumption of a large city, which is why the first projects are springing up in northern Sweden, where hydropower and wind are abundant. The second constraint concerns the ore: direct reduction processes work well with very pure iron ore pellets, with a high iron content and few impurities, and deposits of this quality are a small fraction of those mined worldwide.
That is why other routes are also being studied. One is carbon capture and storage at existing plants, which would allow blast furnaces to keep operating with lower emissions, but it is expensive and so far applied only in limited cases. Another is direct electrolysis of iron ore, in which electric current separates iron from oxygen without the need for a chemical reductant: some companies are developing it, but it is still far from industrial production. None of these solutions will solve the problem on its own. The realistic combination for the coming decades involves more scrap-fed electric furnaces, direct-reduction plants where energy and ore allow, and more careful use of steel in every sector, construction included.
Chemically, direct reduction takes place in the solid state. The ore, in the form of small compact spheres called pellets, is brought to temperatures of about 800–1,000 °C in a shaft reactor through which the reducing gas flows, removing the oxygen from the iron oxides without melting them. The product is so-called sponge iron, porous and rich in metallic iron, which is then melted in an electric furnace together with scrap to make steel. With hydrogen the reaction absorbs heat instead of producing it, and the gas has to be preheated: this too is why electricity demand is so high.
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, after a transitional reporting-only phase launched at the end of 2023, from 2026 requires importers of steel from outside the EU to buy certificates 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.
Beware the "green steel" label
As demand for low-emission materials grows, many offers of "green steel" have appeared on the market, and not all of them mean the same thing. In some cases it is steel actually produced by a low-emission process, such as an electric furnace fed with scrap and renewable energy. In other cases the producer cuts emissions at some of its plants and attributes them, by a method called mass balance, to a share of its sales, certifying as "green" a steel physically produced in the same way as ordinary steel. The method is legitimate as an accounting tool, but it is not the same as buying steel produced differently. For anyone specifying a material, the most reliable guide remains the environmental product declaration of the specific plant, with the values for the production modules. Industry standards are also emerging that classify steel by actual emissions, taking scrap content into account: it is worth asking suppliers which standard their claim refers to. Industry standards are also emerging that classify steel by actual emissions, taking scrap content into account: it is worth asking suppliers which standard their claim refers to.
Finally, there remains the simplest and most often forgotten lever: using less steel. A structure designed with reasonable spans, optimised sections and, where worthwhile, high-strength steels that allow weight to be reduced (European structural steel standards include grades such as S460, almost twice as strong as common S235) can lower a building's footprint more than any choice of supplier. Add to this the reuse of existing elements and design for disassembly, discussed in the piece on the circular economy of steel. Decarbonising the steel industry will take decades and enormous investment; reducing the amount of steel needed is a choice that can be made today, at the drawing board.