Non-energy Emissions in Industry

This page is about process emissions from industry. These are emissions that are direct byproducts of chemical transformations in industrial processes – not from the use of energy to power industrial processes. (We discuss energy use in industry on a separate page.)

The vast majority of industrial process emissions come from just two processes, hydrogen production and cement production.


The world produces 90 million metric tons of hydrogen each year.  Right now, the large majority of this is “grey” hydrogen, produced from methane gas through steam methane reformation. (The “colors” of hydrogen refer to the way that it is made, not to the product itself.  All hydrogen gas is the same.)  In this process, high temperature steam splits the carbon atoms from the hydrogen in methane gas (CH4). The carbon atoms combine with oxygen to create carbon dioxide (CO2), which is released into the atmosphere. Most hydrogen used today is grey because, until the war in Ukraine, methane gas was cheap, and so this has been the cheapest way to produce hydrogen in most parts of the world.  (In some places, it is cheaper to produce it from coal or from petroleum, through even more polluting processes.)

The most straightforward way to produce hydrogen without CO2 emissions is to use an electrolyzer to run an electric current through water (H2O), splitting the hydrogen from the oxygen, producing pure hydrogen gas and pure oxygen.  If zero-carbon electricity is used, then the entire process emits no GHGs.  Until recently, this “green” hydrogen was five to six times more expensive than grey.  However, that is changing quickly, for three reasons:

  1. The main upfront (capital expenditure or “capex”) cost of producing green hydrogen is the cost of electrolyzers.  This is a technology on a learning curve, which means that the cost per unit declines at a fixed rate with every doubling of capacity.  Until recently, the market for hydrogen electrolyzers was small and growing slowly, so prices were decreasing slowly.  But in the last two years, governments and companies around the world have announced massive investments in green hydrogen production – so that the market is now set to grow 6000% by 2031.  This will drive the cost of electrolyzers down the learning curve at unprecedented speeds.
  2. The main operating expenses (“opex”) for green hydrogen production is the cost of renewable electricity.  This, too, is on a learning curve, and so its cost has been plummeting and will continue to do so.  Moreover, because hydrogen can be stored, it can be generated with intermittent renewable energy, like wind and solar, at times when the supply of electricity is greater than demand, so that the electricity is close to free.  This is plan behind the ACES Delta project being built in Utah: green hydrogen will be produced with cheap, excess renewable electricity when it is available, and stored in giant underground salt caverns until it is needed.

⇒ Listen to this great discussion of the ACES Delta project with Jigar Shah, director of the Department of Energy Loan Programs Office

  1. The Russian invasion of Ukraine has increased the price of methane dramatically in many parts of the world – and by a full 700% in Europe.  This means that “grey hydrogen” produced from methane is no longer a bargain.  Even if methane prices come down, it will also a reminder that fossil fuel prices are volatile and unpredictable in a way that electricity from renewable sources is not.

Electrolysis is not the only possible path to decarbonizing hydrogen.  One alternative is to produce hydrogen from methane with steam methane reformation, but then to capture most of the resulting CO2 and pump it into geological formations where it can be permanently stored.  (See our discussion of Carbon Capture, Utilization and Storage, or CCUS, in the page on Energy Use in Industry.) Such so-called “blue” hydrogen has been heavily promoted by the oil and gas industry as a low-carbon bridge, until green hydrogen becomes affordable.  However, as the war in Ukraine has driven up the price of methane, the window of time in which it might be significantly cheaper than green hydrogen has begun to close

One more promising pathway, currently being developed by a startup called Monolith Materials, is methane pyrolysis. Renewable electricity is used to heat methane gas to a very high temperature in the absence of oxygen. The high temperature splits the hydrogen in the methane from the carbon.  Because there is no oxygen present for the carbon to bond with, no CO2 is formed; instead, the carbon becomes an inert solid called “carbon black,” which is a crucial component in tires, ink, and other products, and which is currently produced through a dirty, heavily polluting process.  This way of making hydrogen is close to zero-carbon.  In principle, the process could be carbon negative if enough biomethane (methane made by decaying organic matter) could be sourced to use as a feedstock, in place of fossil methane gas.  In that case, the carbon atoms in the carbon black would come from biomethane that would otherwise have warmed the atmosphere.

Listen to this My Climate Journey podcast interview with Rob Hanson, co-founder of Monolith Materials


Cement is the “glue” that holds concrete together.  It is made by heating limestone to very high temperatures, which causes the Calcium Carbonate (CaCO3) in limestone to split into solid Calcium Oxide (CaO), which is the main ingredient of cement, and carbon dioxide (CO2).   Carbon dioxide produced in this way makes up about 60% of the emissions from cement manufacture. (The other 40% come from burning fuels to produce heat, which we discuss in the page on Energy Use in Industry.)

The most straightforward path to decarbonizing cement is to capture carbon dioxide emissions from the exhaust stream. One start-up, Carbon Cure, aims to recycle these captured emissions and use them to harden or “cure” the concrete that is made from the cement. Alternatively, the captured carbon dioxide might be pumped into geological formations, where it can be permanently sequestered underground. As we discuss in the page on Energy Use in Industry, because carbon dioxide in heavily concentrated in the exhaust stream from cement manufacture, it lends itself more than many other industrial processes to such Carbon Capture, Utilization and Storage (CCUS).

For a really clear, really illuminating overview of approaches to decarbonizing cement and other heavy industries, listen to this Interchange Podcast interview with Dr. Rebecca Dell

Here’s an important point that Dr. Dell makes in the podcast. Depending on how it is made, low-carbon or zero-carbon concrete concrete might be twice as expensive as standard concrete. That sounds like a lot — and for individual cement makers, who have to compete with other cement makes, it is. But cement is cheap: the cost of cement is less than 0.5% of the cost of a construction project. So, regulations that require low-carbon concrete would add almost nothing to cost of projects, even if they doubled the price of cement. And because they would apply to all cement makers equally, they would not hurt cement makers. (An alternative is for governments, which use more cement than anyone, to institute Buy Clean policies for their own purchases – as the Biden-Harris administration, and some US states, are already doing.)

Here’s a great, general explainer on decarbonizing cement from CarbonBrief. It’s from 2018, so it doesn’t discuss the approaches that most recent start-ups are taking

A number of start-ups are working on various strategies for decarbonizing cement. Here are a couple we found interesting.

Listen to this podcast interview with Cody Finke, co-founder of Brimstone Energy.

Listen to this podcast interview with Leah Ellis, CEO of Sublime systems.

This is interesting and all… but I’m not going to work in the cement industry.
What other work needs to be done?

We need people to push for governments at all levels, and also corporations, to adopt Buy Clean policies – or for regulations simply requiring that all cement be low-carbon. These girls show how it’s done: