Brick has a relatively good environmental reputation compared with steel or aluminium: the raw material is abundant, often local clay, transport weighs little on the overall balance, and the CO₂ footprint per kilogram of product — roughly 0.20-0.35 kg CO₂/kg — is markedly lower than for metals. But that figure hides a precise weak point: almost all the energy used in brick production serves a single purpose, bringing and holding a kiln at 900-1,100°C for hours, and that energy today comes almost everywhere from burning natural gas. Decarbonizing brick isn't, as with cement, a problem of binder chemistry — it's a problem of how you generate high-temperature heat without burning fossil fuels.
Why natural gas is still the default choice
Natural gas is the dominant fuel in European brickworks for practical, not ideological, reasons: it burns cleanly and controllably, it allows precise temperature regulation throughout the whole firing cycle (a critical requirement for avoiding defects such as thermal-shock cracking or surface vitrification), and for decades it was the cheapest fuel available for a continuous industrial process like the tunnel kiln. The problem is that every cubic metre of gas burned releases CO₂ into the atmosphere regardless of how efficient the kiln is: the energy efficiency of the tunnel system reduces consumption per tonne of product compared with earlier technologies, but it doesn't eliminate the fossil origin of the heat.
Kiln electrification: the most direct path
The most direct route to zero-direct-emissions firing is electrification: replacing gas burners with electric resistance heating or induction technologies, powered by renewable energy. The conceptual advantage is that renewable electricity today has the fastest and most predictable decarbonization trajectory in Europe — far more so than the availability of alternative fuels at industrial scale. The technical limit is that reaching and uniformly holding 1,000°C across industrial kiln volumes with electric systems requires considerable installed power and a non-trivial infrastructure investment (medium/high-voltage grid connections) for existing plants built for gas firing. The first pilot plants for electrified tunnel kilns are being tested in several European countries, but replacing the entire installed kiln fleet at scale is a process measured in decades, not years, because of the very long service life (30-50 years) of an already-amortized industrial kiln.
Certified biomass and hydrogen: the combustion alternatives
Where direct electrification isn't yet practical, research is focused on lower-impact combustion fuels that could replace natural gas without requiring a full overhaul of the kiln's equipment. Certified biomass (wood residues, olive pomace, other traceable agricultural by-products) is an option already tested in some brickworks in southern Europe, where local agricultural biomass availability is high: the advantage is relatively simple compatibility with existing burners, the limit is the availability and traceability of the raw material at continuous industrial scale. Green hydrogen (produced by electrolysis from renewable energy) is the most ambitious frontier: it burns with no direct CO₂ emissions, but it requires dedicated burners (hydrogen's flame has different combustion-speed and temperature characteristics from methane) and supply and storage infrastructure that doesn't yet exist at wide scale for the ceramics sector. The first trials of firing bricks with hydrogen-methane blends, at increasing hydrogen percentages, are under way at pilot plants in Germany and the United Kingdom.
The product's smaller but not negligible role
Alongside decarbonizing the fuel, there's a second, more modest front that's already practicable today: reducing the energy needed for the same finished-product performance. Optimized multi-chamber thermal blocks, such as the latest-generation Poroton systems, achieve very high thermal performance with lighter mixes, which require less clay mass to be fired per square metre of finished wall for the same thermal transmittance. This isn't an alternative to decarbonizing the kiln — it's a multiplier that makes every improvement in the firing stage more effective, because it's applied to a smaller volume of material for the same building performance.