The two materials most responsible for putting up the modern world, cement and steel, remain among the most difficult to decarbonize, and the persistence of their emissions is becoming one of the more stubborn obstacles to the broader climate ambitions of major economies. Each accounts for a substantial share of global industrial carbon output, and each is produced through processes whose chemistry and economics resist the substitutions that have begun to transform other sectors. The gap between policy targets and what the industries can plausibly deliver in the near term is widening, and the response to it will shape both the credibility of climate plans and the cost of building anything that depends on these materials.

The difficulty begins with the chemistry itself. Cement production releases carbon dioxide not only through the heat required to fire its kilns but also as a direct byproduct of converting limestone into the binding compound that makes concrete possible. Steelmaking from iron ore conventionally relies on coke as both a fuel and a reducing agent, with carbon embedded in the metallurgical process rather than added on top of it. In both cases, the emissions cannot be eliminated simply by swapping in cleaner electricity, because the most consequential reactions occur inside the materials themselves. A genuine decarbonization requires altering how the substances are made, not merely how they are powered.

Alternative processes exist and are advancing. Hydrogen-based direct reduction of iron, electric arc furnaces fed with scrap, novel cement formulations that lower the share of clinker required, and carbon capture installations attached to existing plants all offer paths toward lower emissions. Each, however, faces obstacles. Hydrogen at the scale required is not yet available at competitive cost. Scrap supplies are finite and unevenly distributed. New cement chemistries must satisfy long-established standards before they can be used in structural applications. Carbon capture is expensive, energy-intensive, and dependent on storage capacity that few regions have built out. Demonstration projects are multiplying, but the leap from pilot to industrial scale remains formidable.

The economics compound the difficulty. Both industries operate on thin margins and trade across borders, which means that any producer that adopts a more expensive low-carbon process risks losing market share to competitors who do not. Policy efforts to address this asymmetry, including carbon border adjustments and procurement preferences for greener materials, are taking shape in some jurisdictions but are not yet broad enough to neutralize the disadvantage. Without a level playing field, the firms most willing to invest in decarbonization are also the most exposed to undercutting by those who delay.

Demand patterns add their own pressure. The same regions pressing hardest for emissions cuts are also pursuing housing construction, infrastructure renewal, and the buildout of clean energy capacity, all of which consume cement and steel in large quantities. Wind turbines, transmission towers, rail lines, and the foundations of new factories require precisely the materials whose production remains carbon-intensive. The transition needs the very industries it is trying to transform, and the strain between near-term construction needs and long-term emissions goals shows up in budgets, schedules, and political debates over which targets to soften when they conflict.

Geography matters as well. Cement and steel production has been geographically diversified for decades, with capacity built close to construction markets to limit transport costs, but the most ambitious decarbonization efforts are concentrated in a smaller set of jurisdictions. Producers in regions without strong policy mandates or access to abundant cheap clean energy face fewer immediate pressures to change, and the cost differentials between regions risk shifting production rather than reducing emissions. Effective decarbonization requires coordinated action across borders that the current patchwork of policy does not yet provide.

For policymakers, the materials industries pose a test of whether climate ambitions can survive contact with the harder corners of the industrial economy. The relatively straightforward gains available in power generation and light transport have raised expectations, but extending those gains to heavy industry will require longer timelines, larger investments, and more durable policy support than many plans have so far built in. The realism with which governments and producers approach the challenge, and the willingness to absorb the costs that genuine transformation entails, will determine whether the materials that build the world also build a credible path to lower emissions.