Why We Need Carbon Intensity vs Colors to Measure Hydrogen Emissions

Carbon Intensity Vs Colors

Pink, yellow, green, blue, turquoise, gold: so numerous are the “hydrogen colors” that energy newcomers would be excused for thinking hydrogen a crystal prism, not a colorless gas. And frankly even some old hands seem to have talked themselves into the colors being real. 

Anyone who has come quickly up to speed on the first element knows that the “rainbow” can be a useful tool for keeping production methods straight: pink is nuclear, green is renewably-powered electrolysis, etc. But energy transition advocates who insist on arbitration by rainbow—maintaining that only “green” hydrogen deserves a place in our energy futures—risk missing maximum emissions reductions by focusing too narrowly on particular technologies. Instead, the energy industry should evaluate hydrogen projects by carbon intensity alone.

The Energy Transition Requires Hydrogen Decarbonization…

To combat climate change, we must decarbonize as quickly as possible, and hydrogen-enabled decarbonization is essential to any realistic energy transition plan. First, we must transform hydrogen from an emitter to a decarbonizer. Currently, hydrogen production contributes around 2% of global emissions; ammonia, which can be made from hydrogen, contributes the same. That’s because 95% of hydrogen is made through steam methane reforming without carbon capture, a process which releases some 830 million tonnes of carbon dioxide per year—equivalent to the CO₂ emissions of the UK and Indonesia combined. 

Thankfully, the percentage of hydrogen produced in this way is rapidly shrinking, with current clean hydrogen production and future clean hydrogen projections both rapidly rising. As this supply expands, we fully decarbonize hydrogen supply. Then, we can use hydrogen (and ammonia) to decarbonize hard-to-abate industries.

Using hydrogen to decarbonize aviation, shipping, heavy-duty transport, and cement and steel production, and other industries that cannot be feasibly electrified expands the substance’s emission reduction potential from its current ~4% share of global emissions to something an order of magnitude more impactful. Moreover, these applications can expand energy access globally, driving human development. To achieve this maximum impact, however, we must first minimize the emissions associated with the hydrogen itself.

…Which Requires Scale, Speed, and Affordability

For clean hydrogen to become decarbonization’s industrial workhorse, it must scale at the volume industry demands and at a cost the industry can afford. If we don’t scale volume quickly enough, hydrogen’s potential is compromised for lack of supply. If we don’t scale affordably enough, we struggle to decarbonize because would-be off-takers cannot make the numbers work. 

Renewable-powered electrolyzed hydrogen can, and probably will, play a large role. But to achieve the volume and price point necessary to scale at sufficient speed, then low-carbon-intensity hydrogen must be fair game regardless of energy source.

To Maximize Emissions Reductions, Judge Carbon Intensity, Not Color

Focusing on ‘color’ over deliverability, economics or scalability imposes a deadweight loss on society. Furthermore, pouring money into ‘colors’ that may end up a black hole undermines the overall decarbonization effort. Consequently, hydrogen producers, off-takers, and policymakers should base their production, procurement, and rulemaking decisions on lifetime carbon intensity. By analyzing embodied carbon and emissions from sourcing, production, transportation, and storage, carbon intensity enables a focus on what really matters: emissions reductions.

The Rocky Mountain Institute (RMI), a clean energy think tank, agrees. “A simple color coding is insufficient to clarify the emissions of each production path,” it reports. “Depending on differences in the supply chain and technology performance, two supplies of hydrogen with the same ‘color’ can have widely different carbon footprints.” Importantly, that divergence goes for green hydrogen, too. That’s why we should select hydrogen production methods solely via a quantitative carbon intensity assessment based on Scope 1, 2, and 3 emissions alone.

For Big-Picture Success, Center Big-Picture Realism

Targeting outcomes is essential to optimize the “scale, speed, affordability” triad. And in targeting outcomes, we need to be realists, too. 

Realism involves meeting the world where it is. It also involves ambition, with economics at the forefront. Rather than supporting legacy technology already near the bottom of its cost curve, we must invest in expandable methods with a pathway to subsidy-free economic viability. Only then can we achieve solutions that the developed world can implement without disruption and that the developing world can implement without compromising the growth and energy access they deserve. And to meet those goals, we’ll need technologies that can leverage multiple primary energy sources and be carbon-zero using the prevailing fuels in the world today.

After all, solutions which have the best chance of scaling are the solutions that emitters will implement of their own volition in the long term, and that’s simply a question of dollars and cents. To reach that point with hydrogen, we need to shift focus from colors’ kaleidoscope distraction to focus wholly and simply on carbon intensity.

The Pivot Points of Carbon Intensity

Hydrogen’s emissions fall within five key categories: feedstock, production, transportation, storage, and usage. And there is as much or more variation within each hydrogen “color” as between them. 

Hydrogen produced by electrolysis directly powered by a new renewables array is the gold standard of “clean”. But connect that same electrolysis plant to Texas’s grid, and carbon intensity soars to over 20 kilograms of carbon dioxide per kilogram, nearly double that of natural gas-derived hydrogen without carbon capture and storage (CCS). Even worse is if new “green” electrolyzers cannibalize existing renewable sources, causing grid demand to return to uncaptured fossil generation that then increases net emissions.

Meanwhile, hydrogen produced by steam methane reforming combined with carbon capture (commonly known as “blue” hydrogen) also varies. At the feedstock level, U.S. pipelines lose an average of 1.2% of their natural gas to methane leakage. (Rates are higher – much, much higher – in many other countries.) At the production level, many carbon capture technologies capture less than 60% of steam methane reforming emissions at scale. 

Conversely, responsibly sourced “blue” hydrogen with less than 0.2% methane leakage and 95% or better carbon capture could be just as clean as that from best-in-class electrolysis. And we have good news: the technology exists to meet or exceed both those thresholds. We can achieve less than 0.2% methane leakage and up to 99.9% carbon emissions capture, with improved economics and at tremendous scale, just with technology available today.

Other pivot points of carbon intensity matter not only within colors but across them. We can address emissions from hydrogen leakage, a challenge during both transmission and storage, by converting it to more-transportable ammonia. We can also address leakage by concentrating hydrogen infrastructure in hubs where proximity of supply and demand requires only short-distance transportation and short-duration storage. And saving hydrogen deployment for use cases that cannot be electrified directly abates the opportunity cost of making hydrogen with renewable electricity that could do more good decarbonizing the grid itself.

High Standards, High Urgency

We shouldn’t compromise our standards, but we shouldn’t compromise our opportunities, either. To decarbonize at the scale and the pace needed to combat climate change, we need all the help that we can get, which is why hydrogen that meets strict low-emissions standards must be fair game, no matter its production method. And conversely, hydrogen whose life cycle assessment falls short of emissions standards should not be considered “clean” simply because it stemmed from a made-up color.

With the long average lifetime of a hydrogen plant, the infrastructure we build between now and 2030 will be with us for most of our lifetimes. To avoid stranded assets, we must prioritize carbon intensity in our design choices, investing in sites that pair fossil-based reforming with carbon capture only if the latter can capture more than 95% of carbon emissions from the reforming process. To minimize emissions further, we must also combat leakage: that means both sealing upstream methane leaks and ensuring virtually no leakage of hydrogen or ammonia throughout the value chain. Additionally, we can avert carbon emissions elsewhere on the grid by producing hydrogen by electrolysis only when the electricity source is clean, additional, deliverable, and hourly matched.  

Intense on Intensity

To minimize hydrogen’s emissions and maximize its decarbonization potential, carbon intensity must be top of mind. Quantitatively assessing decision branches at each step of the hydrogen lifecycle will provide producers, off-takers, and policymakers with the information they need to choose a production process without bias.

In short: down with the colors! That way we can be down with carbon intensity, too.


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