Hydrogen is increasingly being touted as the linchpin of the clean transition. In fact, they have created a hydrogen spectrum. This is a list of the types and implications of the different types of Hydrogen, classified by an assigned color. Hydrogen can be employed to generate electricity and power transportation and industrial processes with only water released in the exhausts.
However, not all hydrogen is the same. The climate footprint of hydrogen is solely reliant on its production. To simplify this point, researchers describe hydrogen with a hydrogen spectrum that reflects the production system and related emissions. Here, we describe what each hydrogen “color” represents – and why distinguishing among these colors is important to make climate-friendly choices on energy solutions.
Comprehension of the Hydrogen Spectrum
Hydrogen (H₂) is not an energy source but an energy carrier – an intermediary to contain and transport energy generated elsewhere. Pure hydrogen gas does not exist naturally on Earth; it is released from compounds such as water or fossils and requires energy input to extract these compounds. How clean the hydrogen is as a fuel, thus, depends on the power used to extract it – if fossil fuel power is used to extract it, the hydrogen takes with it a significant carbon footprint; if renewable or nuclear power is used, the hydrogen can be effectively zero-emissions. This reliance created the “colors” of the hydrogen spectrum, a category that indicates the production route and environmental footprint.
Briefly put, the place of hydrogen in an environmentally sustainable future is that of an all-purpose carrier of energy that can power hard-to-electrify sectors – if and only if the hydrogen itself is produced in a clean way. The color palette of the hydrogen spectrum offers a short-hand for this one, from high-carbon “gray” and “black” hydrogen through to low-carbon “green” and “pink”
Hydrogen Spectrum – Methods of Production and Environmental Impact
The hydrogen spectrum color coding is used to quickly communicate how hydrogen is produced and how clean—or polluting—it is. This coding system is very important so that we can truly understand the implications of how hydrogen is produced and the impact on the environment in terms of it’s carbon footprint. Below, we break down the main categories—Gray, Blue, Green, Pink/Purple, White, and Black/Brown— into the hydrogen spectrum classified by their production methods, emissions profiles, environmental implications, and where they currently stand in the marketplace.
Gray Hydrogen
Production Process:
Gray hydrogen is created by extracting hydrogen from fossil fuels, primarily natural gas, through a process called steam methane reforming (SMR). In this process, methane (CH₄) reacts with high-temperature steam to produce hydrogen gas. However, it also generates carbon dioxide (CO₂) and carbon monoxide (CO) as byproducts—none of which are captured.
Byproducts and Emissions:
All CO₂ from this process is emitted directly into the atmosphere, making gray hydrogen highly carbon-intensive. Around 9 to 13 kilograms of CO₂ are released for every kilogram of hydrogen produced. In energy terms, that’s roughly 270 to 390 grams of CO₂ per kilowatt-hour (kWh) of hydrogen energy. While it’s slightly cleaner than hydrogen made from coal, gray hydrogen still has a significant climate footprint.
Environmental Impact:
Gray hydrogen is currently the dominant form of hydrogen production, accounting for about 95{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of all hydrogen made globally and in the U.S. Because it’s cheap and backed by existing infrastructure, it remains the default choice for industries—despite being a significant source of emissions. Gray Hydrogen’s place in the hydrogen spectrum is often labeled “dirty hydrogen” due to its fossil fuel origins.
Market Status:
This method of hydrogen production is well-established, commercially viable, and currently the most cost-effective, with bulk production typically ranging from $1–2 per kilogram. Industries such as oil refining and fertilizer production rely heavily on gray hydrogen because of the high volumes they require. But as the global push for decarbonization grows stronger, gray hydrogen’s dominance is expected to decline. The size of the Gray hydrogen spectrum is shrinking. Continuing to use it clashes with international climate targets because of its heavy CO₂ output.
Blue Hydrogen
Production:
Blue hydrogen is produced using the same process as gray hydrogen—usually steam methane reforming (SMR) of natural gas—but with one significant addition: carbon capture and storage (CCS). This technology is designed to trap the CO₂ usually released during production. In theory, it prevents most of those emissions from reaching the atmosphere. The hydrogen-making process is identical to gray hydrogen, but with the key difference that a large portion of the CO₂ is either buried underground or reused in other ways. There is room for improvement in the blue hydrogen spectrum.
Byproducts and Emissions:
In a best-case scenario, blue hydrogen could capture about 90{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} or more of the CO₂ that gray hydrogen would emit. That would lower emissions to roughly 1–4 kg of CO₂ per kilogram of hydrogen produced—or around 30–120 grams of CO₂ per kilowatt-hour. That’s a big improvement over the 10+ kg associated with gray hydrogen. However, the reality often falls short. For example, Shell’s Quest facility in Canada—a major blue hydrogen plant—has only managed to capture 43{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of its CO₂ output.
That means most of the emissions still escape. At an average 50{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} capture rate, blue hydrogen still releases about 5–9 kg of CO₂ per kg of hydrogen, which isn’t drastically better than gray. Add to that the issue of methane leaks during natural gas extraction and transportation—a potent greenhouse gas—and the climate benefits of blue hydrogen start to shrink. There are still many issues in the blue hydrogen spectrum.
Environmental Impact:
While blue hydrogen is often promoted as a “low-carbon” option, its actual environmental impact depends heavily on how well carbon is captured and how methane leaks are managed. Done right, it can cut emissions by 75{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} or more compared to gray hydrogen. But critics point out that, so far, large-scale projects haven’t proven they can consistently capture high percentages of CO₂. As of the early 2020s, only a handful of blue hydrogen plants are running globally—and even the best performers haven’t reached optimal capture rates. That makes the label “blue” somewhat questionable unless near-total carbon capture is truly achieved. Another reason for improvements in the blue hydrogen spectrum.
Market Status:
Blue hydrogen is gaining traction but isn’t widespread yet. It’s often viewed as a stepping-stone—letting industries keep using fossil fuels while reducing emissions compared to gray hydrogen. Several blue hydrogen projects are in the pipeline, many supported by oil and gas companies or national governments. For example, under certain conditions, the International Renewable Energy Agency (IRENA) suggests that blue hydrogen could make up a sizable portion of the global hydrogen supply by 2050.
Still, for now, it’s in the demonstration phase. The SMR and CCS technologies are known quantities, but capturing carbon affordably and reliably at scale remains a significant challenge. Whether blue hydrogen gains a firm footing will depend on how carbon pricing, climate regulations, and CCS technology evolve. If all those stars align, blue hydrogen might find a place. If not, the world may opt to leapfrog directly to green hydrogen. That would be the best improvement in the blue hydrogen spectrum.
Green Hydrogen
Production Process:
Green hydrogen is produced through water electrolysis powered entirely by renewable energy. During this process, an electric current—sourced from solar, wind, hydro, or similar renewable sources—is used to split water (H₂O) into hydrogen and oxygen in a device called an electrolyzer. Since there’s no fossil fuel involved, the process generates zero direct carbon emissions. Because of this, green hydrogen is often referred to as “clean hydrogen”—especially when renewables are the sole power source. Let’s all promote and raise awareness for the Green hydrogen spectrum.
Byproducts and Emissions:
The only byproduct of green hydrogen production is oxygen (O₂). No greenhouse gases are released at the production site, and the hydrogen is essentially carbon-free as long as the electricity comes entirely from renewable sources. (There are minor emissions involved in manufacturing the electrolyzers and renewable infrastructure, but they’re very small on a per-unit basis.)
It’s important to note that if hydrogen is produced using grid electricity—which often includes fossil fuels—the result isn’t truly “green.” (That’s not a good thing for the green hydrogen spectrum). For instance, using the average U.S. grid mix could yield more than 20 kg of CO₂ per kilogram of hydrogen. That’s what is sometimes called “gray hydrogen via electrolysis.” Authentic green hydrogen, by contrast, is powered solely by dedicated renewable energy and carries near-zero carbon intensity.
Environmental Impact:
Green hydrogen has the lowest environmental impact of all hydrogen types—essentially zero emissions during operation. That makes it the gold standard for meeting climate targets. If hydrogen is to play a meaningful role in helping the world reach net-zero emissions, most of it will need to be green (or from other zero-carbon pathways like pink or white hydrogen). One downside is the high energy demand: it takes about 50–55 kWh of electricity to produce 1 kg of hydrogen.
This means that a substantial increase in renewable power capacity is needed to scale up production. Today, the green hydrogen spectrum makes up only about 1{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of global hydrogen output, mainly from pilot projects. This low share is largely due to historical costs, which have been significantly higher than gray hydrogen. But that’s changing fast. (Looking better for the green hydrogen spectrum all the time.) As renewables get cheaper and electrolyzer tech improves, green hydrogen becomes more affordable and accessible.
Market Status:
Green hydrogen is currently in its early growth phase. Governments and companies worldwide are pouring resources into scaling it up as part of their decarbonization strategies. Both the U.S. and the European Union have launched significant initiatives—including funding programs and regional “hydrogen hubs”—to support its development. While only ~1{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of hydrogen was green as of 2020, the International Energy Agency and other analysts predict massive growth in green hydrogen capacity by 2030.
The industry is moving from small-scale systems to large plants—hundreds of megawatts and more—being built in places like Europe, North America, the Middle East, and Australia. Green hydrogen is widely seen as the long-term solution: the clean, fully decarbonized version of hydrogen production. The main hurdles are bringing costs down (to around $1–2/kg by 2030, from today’s ~$4–6+) and ensuring there’s enough renewable electricity to power the electrolyzers at scale. Push hard for the green hydrogen spectrum.
White Hydrogen
Production Process:
White hydrogen refers to naturally occurring hydrogen that forms underground through geological processes. In some rare locations, chemical reactions—like water interacting with iron-rich rocks—can create hydrogen gas that collects in underground pockets, much like oil or natural gas. In other cases, small amounts of hydrogen may be released as a byproduct of certain industrial processes. The key distinction is that no intentional production process, like electrolysis or reforming, is used. White hydrogen is simply extracted from nature rather than made by human-engineered systems. Here’s hoping we can develop a solution for the white hydrogen spectrum.
Byproducts and Emissions:
If you could tap into underground stores of white hydrogen directly, there would be almost no emissions involved—just the energy needed for drilling and extraction. Since no combustion or chemical reaction produces the hydrogen, there’s no associated CO₂ from its creation. In that sense, white hydrogen could be considered truly “zero-carbon,” with the Earth itself having done the hard work of making it. That said, any emissions or pollution would depend on the methods used to extract and process it—especially if other gases are present in the reservoir. The white hydrogen spectrum is also dependant of the methods of the drilling process.
Environmental Impact:
In theory, white hydrogen is a dream fuel: no production emissions, no feedstock input, and no chemical waste. But the catch is availability. Unlike oil or natural gas, there are currently no major proven reserves of white hydrogen being commercially extracted. Only a few natural hydrogen seeps have been discovered—like one in Mali—which has sparked growing scientific and commercial interest. If white hydrogen proves abundant and accessible, it could revolutionize clean energy. Until then, it remains speculative. There’s also a concern that tapping into underground hydrogen could unintentionally release other greenhouse gases or disrupt ecosystems if not appropriately managed.
Market Status:
At present, white hydrogen has no commercial presence in the hydrogen market. No large-scale extraction operations exist, and the infrastructure to harvest it is virtually nonexistent. However, research into natural hydrogen is ramping up, with geologists exploring potential reservoirs and companies investigating whether it could become the next big clean fuel.
Some have even dubbed it “gold hydrogen,” comparing the potential to a modern-day energy gold rush. But for now, white hydrogen is more of a scientific curiosity than a real player in the energy transition. If future discoveries pan out, it could change the game. In my opinion, the white hydrogen spectrum should be a task for the world’s future “To do list.” Until then, the focus remains on produced forms like green, pink, or (less ideally) blue hydrogen.
Pink/Purple Hydrogen
Production method:
Pink (alternately referred to as purple or red) hydrogen is made by electrolysis with nuclear power. That is to say that a nuclear power station supplies the power (and potentially heat too) to break water into hydrogen using electrolysis. The “pink” name is usually applied when discussing conventional electrolysis with nuclear power. Meanwhile, “purple” can refer to versions such as employing both nuclear heat and power to maximize the efficiency (or just an alternative name.)
The use of these color descriptions is still developing. Either way, the same water electrolysis is used to produce the hydrogen, just with a non-fossil power source. All in all, I believe that the Pink hydrogen spectrum is highly contravercial in today’s global society. Overall, Nuclear Energy is statistically safe, but when there is a catastrophe it is very serious.
Byproducts and emissions:
As with green hydrogen, pink/purple hydrogen’s sole direct byproduct is oxygen. Emissions of CO₂ are effectively zero because nuclear reactors don’t emit any CO₂ when operating. The big difference with green hydrogen is that the source of nuclear power is not renewable (using mined uranium fuel), but it is an energy source with very little carbon. Nuclear power life-cycle emissions (coal mining to plant construction and so on) are extremely low – on the same level as wind power in grams of CO₂/kWh. The hydrogen itself is, therefore, similarly low-carbon. No air pollutants or greenhouse gases are released during H₂ production itself.
Environmental footprint:
Pink hydrogen is considered a low-carbon hydrogen similar to green hydrogen. It does not add to climate change through production emissions. It takes advantage of the steady power generation from the around-the-clock operation of power plants that can be an asset: Nuclear-powered electrolysis can operate continuously and could use off-peak reactor capacity to produce hydrogen. Large amounts of hydrogen could be produced without carbon emissions in this way. Environmental trade-offs usually arrive with nuclear power – production of radioactive waste and issues with safety.
But on the front of greenhouse gases, pink/purple hydrogen is on the same level as green hydrogen. Some think that hydrogen sourced from nuclear is an alternative to hydrogen sourced from renewables, particularly in nations with sizable nuclear fleets or with little access to renewables. For example, France and the United Kingdom have considered “pink” hydrogen schemes based on utilizing those nations’ existing nuclear plants and we are experimenting with hydrogen production within existing U.S. reactors.
Market status:
Pink/purple hydrogen is still in its infancy. Small demonstration plants exist but with no large commercial hydrogen production based on nuclear power to date. It is still an attractive notion, particularly to utilize nuclear plant power when electricity demand is low. The electrolysis technology is off-the-shelf (no different from green hydrogen), so the biggest hurdle is economics and strategy.
Is it economically sound to utilize valuable nuclear power to make hydrogen rather than to input it into the grid? As the overall hydrogen spectrum economy takes off, we could see dedicated nuclear-to-hydrogen plants or dual-modular operation of reactors. The maturity level is high on the tech side (as both nuclear and electrolysis are mature technologies separately) and low on the deployment side. In short, the pink hydrogen spectrum has strong carbon credentials and could be significant in the energy mix in nations with nuclear power, albeit it is presently in an early adoption stage.
Black/Brown Hydrogen
Production Process:
Black and brown hydrogen are produced through coal gasification—a process where coal is subjected to high temperatures and limited oxygen to create a synthetic gas, or “syngas,” made up of hydrogen, carbon monoxide, and carbon dioxide. The difference between black and brown hydrogen comes down to the type of coal used: black hydrogen uses bituminous or anthracite coal (the “hard” black variety), while brown hydrogen uses lignite, a softer and lower-grade coal with higher moisture content.
Byproducts and Emissions:
The environmental downside of black and brown hydrogen is significant. When coal is gasified, it releases large amounts of CO₂—and without carbon capture, all of it is emitted into the atmosphere. These methods also produce other pollutants, such as sulfur compounds and heavy metals, depending on the type of coal and the gasification controls in place. Regarding emissions, black/brown hydrogen is the worst offender on the color spectrum—producing around 18 to 25+ kg of CO₂ for every kilogram of hydrogen. That’s roughly twice as polluting as gray hydrogen made from natural gas. The Black hydrogen spectrum is a monster.
Environmental Impact:
From a climate perspective, the black and brown hydrogen spectrum is an environmental non-starter. Not only do they have the highest carbon footprint, but coal mining and processing also cause major local environmental damage—air pollution, water contamination, and land degradation. Producing hydrogen this way essentially erases any of the clean benefits hydrogen is supposed to bring. In fact, you’d emit less CO₂ by just burning natural gas directly than going through coal gasification to make hydrogen. This method is incompatible with a climate-conscious future unless carbon capture is added (which is rare).
Market Status:
Black and brown hydrogen are relics of a previous era. In the early 20th century, coal-based hydrogen—often part of “town gas”—was commonly used for heating and lighting in cities. But as cleaner and more efficient methods emerged, coal-to-hydrogen largely disappeared. Today, only a few niche projects still explore this pathway, mostly in places with abundant coal and limited access to natural gas. One example is a pilot project in Australia to convert brown coal to hydrogen for export to Japan. Even that has been heavily criticized due to its emissions, though future phases aim to incorporate carbon capture.
Overall, this form of hydrogen is seen as outdated and environmentally unsustainable. It’s unlikely to play any meaningful role in the future hydrogen economy unless drastically improved with carbon capture—and even then, it may be outcompeted by cleaner options. In short, black and brown hydrogen serve as a cautionary tale: a reminder that not all hydrogen is created equal and that the path to a cleaner energy future must steer away from carbon-heavy fuels like coal.
Hydrogen Color Spectrum: A Visual Summary
To quickly compare the different types of hydrogen, here’s a simplified breakdown based on their production source, emissions, advantages and disadvantages, and current market status:
| Color | Production Source | Emissions Estimate | Pros/Cons | Market Status |
| Gray | Natural gas (SMR, no carbon capture) | ~9–13 kg CO₂ per kg H₂ (high) | ✅ Cheapest today, established tech ❌ High emissions, fossil fuel-based | Dominant (≈95{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of current hydrogen production) |
| Blue | Natural gas + carbon capture (SMR + CCS) | ~1–4 kg CO₂ per kg H₂ (if ~90{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} captured) | ✅ Lower emissions than gray ❌ Methane leaks + incomplete capture reduce climate benefit | Emerging, pilot to early commercial stage |
| Green | Renewable electricity + electrolysis | ~0 kg CO₂ (if 100{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} renewable) | ✅ Truly sustainable, zero-emissions ❌ Costly today, needs massive renewable expansion | Growing fast, ~1{0dba32929e04307161346db70f6576455890e3bd9f75d81cb63ac96a315b4d8c} of current production, large scale expected |
| Pink/Purple | Nuclear electricity + electrolysis | ~0 kg CO₂ (nuclear = low-carbon) | ✅ Reliable 24/7 power, zero emissions ❌ Nuclear waste/safety concerns | Nascent, pilot projects underway |
| White | Naturally occurring underground hydrogen | ~0 kg CO₂ (if directly extracted) | ✅ Zero production emissions ❌ Rare, speculative, no commercial extraction | Not commercially developed |
| Black/Brown | Coal gasification | ~18–25+ kg CO₂ per kg H₂ (very high) | ✅ Historically cheap feedstock ❌ Highest emissions, severe pollution | Largely phased out or limited to niche legacy projects |
Why Green Hydrogen Is the Future Hydrogen Spectrum
Green hydrogen is the only widely scalable option that aligns with global climate goals. Since it’s made with renewable energy and doesn’t emit CO₂, it’s the most effective way to decarbonize sectors that are hard to electrify—like steel, shipping, aviation, and long-haul trucking. Green hydrogen becomes essential as countries push toward net-zero targets under agreements like the Paris Accord.
- Extending the Reach of Renewables:
Electricity can’t power everything directly. Green hydrogen acts as a bridge—it allows clean energy to fuel processes that require heat, chemicals, or long-term energy storage. For example, hydrogen-based fuels can power planes, and green ammonia (made from green hydrogen) can be used in agricultural fertilizer without fossil fuels. It’s a way to store and distribute renewable energy more flexibly across the economy. - Technological Momentum:
Costs for both renewables and electrolyzers are dropping quickly. With innovations in solar, wind, and hydrogen production tech, green hydrogen is expected to reach cost parity with gray hydrogen within the next decade—possibly around $1–2 per kg by 2030. Governments and industries are already investing billions in scaling up capacity and infrastructure, from hydrogen hubs to fueling stations. - Local and Decentralized Production Potential:
Green hydrogen can be produced anywhere with sunshine or wind. That reduces dependence on fossil fuel imports and enhances energy security. It also opens up possibilities for microgrids—local, self-sufficient systems where surplus solar or wind power can be converted into hydrogen for backup power or zero-emission transportation. (Imagine living in urban areas without that nasty brown cloud.) - Verification and Trust through Innovation:
One concern is proving that hydrogen labeled “green” is genuinely produced with renewables. That’s where digital tools like blockchain come in. Platforms such as Farad Connect use blockchain to track each renewable energy unit used to make green hydrogen. These verified digital “tokens” help to build trust in green credentials, enabling carbon trading and potential financial incentives for clean producers.
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Conclusion: The Hydrogen Spectrum That Points to a Cleaner Future
The hydrogen spectrum isn’t just a clever naming scheme—it’s a critical tool for understanding the climate consequences of how hydrogen is made. While hydrogen burns cleanly, it only benefits the planet if it’s produced cleanly too. That’s where green, pink, and white hydrogen shine. Blue hydrogen may have a transitional role, but it’s not without environmental caveats. Black and brown hydrogen, with their massive emissions, represent the past—not the future.
By favoring green hydrogen and supporting verification platforms like Farad Connect, we can build a trustworthy, emissions-free hydrogen economy that truly contributes to climate solutions. The green hydrogen spectrum isn’t just the cleanest—it’s also the brightest path forward.