The huge climate problem of cement, steel and chemicals, visualized

These three materials are essential, carbon-intensive and produced in mind-bogglingly large quantities.

This article is part of our special series "The Tough Stuff: Decarbonizing steel, cement and chemicals." Get caught up here.

Cement, steel and chemicals are some of the most extensively produced materials in the world. They’re also among the largest global sources of carbon emissions — manufacturing them releases more CO2 into the atmosphere each year than all of the emissions generated by the United States.

These materials are so emissions-intensive not just because of how they’re made, but also because of how much of them the world uses. Here’s how the annual production of cement, steel and chemicals stacks up against one of the most notoriously massive things in the United States, the Grand Canyon: 

(Source: International Energy Agency, RMI)

Concrete — the main end use of cement — is the most abundant manufactured material on the planet. It’s strong, durable and easily molded into different shapes, which is why various forms of it have been used for millennia as a key component of humanity’s built environment. Cement makes up just 10 to 15 percent of concrete by volume, but it is responsible for about 90 percent of concrete’s carbon emissions. In 2022 alone, the world produced more than 4 billion metric tons of cement, a 27 percent increase from 2010. Put that all together, and it would form a cube that measures more than 4,500 feet on each side. 

Steel, an iron alloy, can be found in nearly everything you look at, from kitchen appliances to cars to buildings, bridges and other everyday infrastructure. It’s also instrumental to clean energy technology and can be found in equipment such as wind turbines and solar panel racking. Last year, 1.9 billion metric tons of steel were produced around the world. 

Chemicals span a more diffuse array of end-use applications, but they are just as ubiquitous as steel and cement. The fertilizer that enables global food production, the fabrics used to make clothes and the plastic that goes into countless consumer products all rely on fossil-fuel-derived chemicals. Production of several of the so-called primary chemicals — ammonia, methanol and high-value chemicals” such as ethylene and propylene — amounted to nearly 700 million metric tons last year. Although that’s much less than the amount of cement and steel produced, it still far outpaces most other materials. For example, the production of chemicals surpassed aluminum production by a factor of seven last year in weight.

How much carbon dioxide do cement, steel and chemicals emit?

The staggering production volumes of cement, steel and chemicals are at the core of the calamitous climate problem posed by heavy industry. Over one-quarter of global emissions result from industrial processes — more than from all forms of transportation combined — and that figure is driven mainly by these three materials.

Within the category of global industrial-sector emissions, iron and steel production are the most carbon-intensive processes, responsible for nearly a third of emissions in the sector, followed closely by cement. Chemicals make up a comparatively smaller share of industrial emissions, coming in at 15 percent. 

But the same breakdowns don’t always apply when you zoom in on a particular country. 

Take the U.S., for example. It’s the world’s largest chemicals producer, and its emissions from that industry far outpace those generated by its domestic steel or cement production. In part, this is because the U.S. relies more heavily on electric arc furnaces to make steel than other countries do — an approach that is less polluting than traditional coal-blast furnaces. Cement emissions are also proportionately lower in the U.S., mostly because the country is simply building less infrastructure than rapidly developing economies such as China. 

Cement production is relatively localized, and there’s a natural cycle as a country develops and builds out its infrastructure and housing [when] there is a lot of cement usage — we just saw China go through that. But once the country has created that infrastructure, there is a bit of a decline in demand. So the U.S. is just further along; we have much more built-out infrastructure at this point,” said Ben Skinner, a manager on the concrete and cement team in think tank RMI’s Climate-Aligned Industries practice. (Canary Media is an independent affiliate of RMI.) 

But regardless of where the steel, cement or chemicals are produced, one thing remains true: Making these materials requires a lot of heat, some of it at temperatures too high for existing electrified alternatives to reliably and cost-effectively provide. 

Steelmaking is the clearest example of this problem. Most of its emissions come from making iron, the main component of steel. Iron is extracted by smelting iron ore with coke and limestone in blast furnaces at around 2,800 degrees Fahrenheit or higher. But turning that iron into steel also requires subjecting it to one of two high-temperature processes: mixing the iron with fluxes and scrap and injecting it with oxygen to remove impurities, or using an electric arc furnace to melt reclaimed scrap. In the U.S., nearly three-quarters of steel’s total emissions stem from these high-heat processes, despite the ubiquity of less-polluting electric arc furnaces in the domestic steelmaking industry.

Many of the near-term solutions for reducing the carbon footprint of steel production focus on increasing the use of electric arc furnaces and recycled steel or replacing the use of coal as a fuel source with fossil gas coupled with carbon capture. More aspirationally, there’s a push to figure out alternative ways of creating primary iron, such as using green hydrogen to produce direct-reduced iron, said Jessica Terry, a manager on the steel team at RMI’s Climate-Aligned Industries.

Cement-making requires carbon-intense heating as well. To make Portland cement, the most common type of cement used globally, limestone and clay need to be heated together in a kiln to about 2,500 degrees Fahrenheit. But a bigger problem with making cement is what’s known as process” emissions. Because limestone contains a lot of carbon, the process of heating it results in a chemical reaction that releases carbon dioxide. So even if the heat could be generated by a carbon-free source — a major challenge in itself — cement production would still result in a substantial amount of CO2 emissions.

One key near-term solution for decreasing cement emissions is simply to use less of it in concrete, said Skinner. You can use supplementary cementitious materials, like clay — these are materials that behave like cement but aren’t cement, so they don’t have the same associated emissions,” added Skinner. Major cement-makers, including Holcim, are already cutting their emissions using this approach, while several startups are exploring entirely new zero-carbon ways of producing cement.

When it comes to making chemicals, emissions are more evenly distributed across the production process, though the biggest portion — 40 percent — also comes from generating heat. The second-biggest chunk — nearly 30 percent — comes from the use of fossil-fuel-derived electricity in the manufacturing process, and another 24 percent stems from process emissions. Another layer of complexity comes from the fact that many of the primary raw materials, or feedstocks, used to make chemicals are carbon-based fossil fuels — mostly oil and gas. That means chemicals production generates emissions not only from the manufacturing process itself but also from the activities of upstream suppliers, also known as Scope 3 emissions.

With chemicals, you can’t actually decarbonize because carbon is the backbone of all of our chemical products,” said Brianne Cangelose, a manager in RMI’s Climate-Aligned Industries unit. Everything we use for modern-day life and health requires chemical derivatives.” 

She said the main focus areas for curbing emissions from chemicals are diversifying their feedstocks away from fossil gas and oil to alternatives such as biogenic carbon, and slashing heat and process emissions through electrification coupled with clean energy and, in small amounts, carbon capture. 

Cleaning up cement, steel and chemicals is crucial

While companies work on technical solutions to these problems, policymakers have started to move toward encouraging the adoption of lower-carbon steel, cement and chemicals through subsidies and incentives.

In the U.S., the Inflation Reduction Act offers targeted federal incentives for industrial decarbonization, particularly through the hydrogen production tax credit, which is expected to make low- and zero-carbon hydrogen financially viable. The landmark climate law also includes tax credits for carbon capture and sequestration at industrial facilities, which could be especially significant for cement and chemicals manufacturing. The Biden administration launched the Industrial Demonstrations Program this year, with $6 billion from the IRA and the Bipartisan Infrastructure Law to fund companies working on decarbonizing heavy industry. 

But despite such steps, these materials are expected to emit about as much carbon dioxide a decade from now as they do today. In fact, industry is set to overtake both transportation and electricity generation to become the largest source of U.S. emissions by 2035, according to The Rhodium Group.

Experts say there is no single solution to the problem of industrial emissions. Instead, it will demand a multipronged response that encompasses everything from policies that incentivize the government and corporations to buy lower-carbon materials to technological breakthroughs that enable deep decarbonization. And all of these strategies must be carried out at a pace that matches the urgency of the climate crisis.

We’re looking at problems where we have to build entirely new networks of production. How do we consider different fuel supplies? How do we reinvent methods we’ve used for a long time?” Terry said. How do we transition to something new while bridging the gap? That’s why this is such a big problem.”

Throughout this week, Canary Media will showcase the most promising solutions to decarbonizing these industries — and the biggest barriers standing in the way of each. Follow the coverage here.