Blue Hydrogen vs Green Hydrogen vs Grey Hydrogen: What's the Difference in Carbon Intensity

Why Hydrogen Colours Don't Tell You What You Need to Know

The hydrogen rainbow exists for a reason. The energy industry needed a way to distinguish production methods, like fossil-based, fossil-with-capture, and renewables-based. Colour labels gave the market a common language. Thatlanguage never went away. It’s unhelpful, and has never been precise enough to support the commercial decisions the market now needs to make.

The green hydrogen vs blue hydrogen difference, for example, implies a clear hierarchy. But that's not true. A green hydrogen project powered by a carbon-heavy grid can carry a higher CI than a well-run blue hydrogen facility with strong methane controls. Meanwhile, a blue hydrogen plant with a low capture rate and leaky upstream gas supply can perform worse than its low-carbon label suggests.

Put simply, colour tells you the general production method. It does not tell you how many kilograms of CO₂e were actually emitted per kilogram of hydrogen produced.

For procurement teams, investors, and ESG leads making real financial and compliance decisions, that number is what matters. CI, measured in kgCO₂e/kgH₂ for hydrogen, or tCO₂e/tNH₃ for ammonia, is the metric that makes comparison possible and holds up under scrutiny.

Carbon Intensity 101

Carbon intensity measures greenhouse gas emissions per unit of output. For hydrogen, it's expressed as kgCO₂e per kg of H₂ produced. For ammonia, it's tCO₂e per tonne of NH₃ (or kgCO₂e/kgNH₃).

Unlike total emissions reporting, CI is output-normalised, which makes it far more actionable when comparing suppliers, projects, or pathways.

CI has moved well beyond ESG reporting. It now shapes commercial contracts, informs price premiums, determines compliance eligibility under frameworks like the EU's Renewable Fuel of Non-Biological Origin (RFNBO) standards and CBAM, and influences capital allocation decisions.

If you're structuring a hydrogen offtake agreement or building an investment thesis around ammonia, CI thresholds are likely written into the terms. (If they're not, they should be.)

Grey vs Blue vs Green Hydrogen—What Each Pathway Actually Means

Before you can assess CI, you need to know the various production pathways and where emissions come from. Not all hydrogen is created equal, even within the same colour category.

Grey Hydrogen (Baseline)

Grey hydrogen is produced via steam methane reforming (SMR) or autothermal reforming (ATR) of natural gas, with no carbon capture. The process splits methane into hydrogen and carbon monoxide (and ultimately carbon dioxide), releasing the emissions directly into the atmosphere.

Two factors dominate grey hydrogen's carbon footprint: Process CO₂ from SMR/ATR, and upstream methane leakage from the natural gas supply chain. Methane is a potent greenhouse gas, and even small leak rates compound significantly over a 20-year warming horizon.

Blue Hydrogen (With Carbon Capture and Storage)

Blue hydrogen production adds carbon capture and storage (CCS) to the SMR or ATR process, preventing most CO₂ emissions from reaching the atmosphere—at least in theory.

In practice, CI ranges vary, and the gap between the best and worst performers is substantial. What drives that variance? What's captured (process vs. combustion), capture rate, methane leakage, electricity source, boundaries, and the long-term integrity of storage.

Blue hydrogen production can range from genuinely low-carbon to barely better than grey, depending on these inputs. A buyer who selects on colour alone has no way of knowing which end of that range they're actually buying from. As such, it's important to understand the details.

Green Hydrogen (Electrolysis)

Green hydrogen is produced through a process called electrolysis, i.e., using renewable electricity to split water into hydrogen and oxygen. In green hydrogen production, carbon emissions come from the power used to run the electrolyser.

Green hydrogen produced using dedicated, additional renewable capacity, like verified solar or wind power with strong temporal matching, can achieve very low CI. But green hydrogen produced using grid electricity with a high fossil fuel mix can carry a surprisingly high CI.

In other words, the label "green" describes the intended method, not the verified outcome. Green carbon doesn't automatically mean zero — or even low — carbon emissions.

What Actually Drives Carbon Intensity Differences

CI differences within and across pathways come down to a few controllable factors. Understanding them separates informed procurement from colour-coded guesswork.

1. Methane Leakage—The Hidden Lever for Grey and Blue Hydrogen

Methane leakage from natural gas supply chains is a significant driver of hydrogen CI. Small changes in the assumed leak rate produce large swings in final CI figures.

For example, a blue hydrogen facility that draws from a high-leakage upstream basin may have a worse carbon footprint than advertised, particularly when assessed over a 20-year time frame.

Look for measured data from actual supply chains, not generic defaults from lifecycle databases. If a supplier can't tell you where the gas comes from, and its independently verified leak rate, use caution.

2. Electricity Sourcing—The Hidden Lever for Green and Blue Hydrogen

Renewable electricity is the story for green hydrogen. But the term "renewable" needs to be unpacked.

Grid-average accounting, vague certificates that claim renewable energy sources without time or location alignment, and temporal mismatches between electricity consumption and renewable generation can inflate the apparent greenness of a project.

Electricity matters for blue hydrogen too, as it powers capture systems, compressors, and auxiliary equipment that adds to a facility's Scope 2 footprint. A blue hydrogen plant running its CCS system on coal-heavy grid power will have a higher CI than one using clean power generation.

3. CCS Boundaries and Capture Rate

Capture rate is not the same as system-wide capture. A facility might claim a 90% capture rate on process CO₂ while never accounting for combustion emissions. Transport and storage of captured carbon also carry their own emissions and permanence risks.

Procurement teams evaluating blue hydrogen should require the capture rate and configuration, a clear statement of which emission sources are within the CCS boundary, and evidence of storage integrity.

4. System Boundaries and Accounting Rules

Suppliers can report very different CI figures for similar facilities. They simply have to use different system boundaries. Well-to-gate, cradle-to-gate, and full lifecycle assessments yield different numbers. What really matters is boundary consistency across suppliers.

When procuring hydrogen, require boundary documentation as a minimum standard in any CI comparison. Without it, headline numbers are unreliable.

Hydrogen Deep Dive—Where Carbon Intensity Can Be Misleading

Significant CI variation exists, even within colour categories.

Blue Hydrogen: When "Clean" Can Still Be High-CI

Blue hydrogen is a low-carbon transition fuel, but only under the right conditions.

High CI in blue hydrogen fuel typically follows a low capture rate, a high-methane-leakage supply basin, or grid-powered capture systems with high carbon intensity.

When assessing blue hydrogen, require a minimum data set that includes methane basis, capture configuration, energy mix, boundary standard, and storage evidence details.

Green Hydrogen: Why Renewable Claims Don't Automatically Equal Low CI

Not all green hydrogen has the same carbon intensity.

If a project uses grid electricity without dedicated renewable capacity or verified additionality, its CI depends on the grid mix, which could be far from zero.

A procurement red flag is vague renewable energy certificates without time or location alignment. Efficient electrolysis technology matters too, but it's secondary to power sourcing.

Ammonia Deep Dive—Why CI Comparisons Get Even Harder

Ammonia is an energy carrier and a fertiliser feedstock. It's increasingly central to long-distance hydrogen transport and the energy transition. But ammonia CI comparisons are complex.

Most of ammonia's carbon footprint comes from the hydrogen used to produce it. So, hydrogen CI drives the overall number. But plant energy integration, nitrogen separation energy, and how CI is allocated across co-products add further layers. "Blue ammonia" and "green ammonia" face the same boundary and verification challenges as their hydrogen equivalents.

The scale of the problem is visible in the data. Two ammonia facilities both labelled "blue" can have carbon intensities ranging from 0.61 to 1.95 tCO₂e per tonne of ammonia — a difference of more than three times. And this isn't an edge case. It reflects the real distribution of performance across active commodity markets today, where colour labels are being used to trade at premiums with no consistent definition underpinning them.

"Good" ammonia discloses hydrogen CI with clear methodology, plant-level CI and allocation rules, and verifiable electricity and gas sourcing for the full production process.

Commodity Colour Labels and Where the Market is Heading

Commodity markets have solved analogous problems before. Crude oil was once priced as a single commodity, but the sulphur component became measurable, then tradeable, and finally a core component of price. Today, sulphur differentials are standard in crude valuation — and while the market still uses "sweet" and "sour," those terms now have precise, standardised thresholds behind them.

Carbon intensity in hydrogen and ammonia needs to follow the same path. Rather than broad colour buckets that obscure the real range of performance, the market needs a continuum of standardised carbon intensity — where facilities and cargos are measured and compared like-for-like, and where every kilogram of CO₂e improvement carries commercial value.

The voluntary carbon market has already made this shift. A few years ago, credits were sold by project category, with little financial differentiation for quality. Today, there is a clear price premium for high-quality credits that reflect genuine emissions reductions. 

The signals from hydrogen and ammonia buyers and producers suggest commodity markets want to make the same transition. The infrastructure to support it — independent, standardised, facility-level CI data — is what's been missing.

A Practical Buyer/Offtaker Checklist: How to Compare CI Across the Energy Landscape

This checklist will help you move from colour labels to decision-grade data when evaluating hydrogen and/or ammonia suppliers in 2026 and beyond:

Methodology disclosure

• Require the accounting standard, version, and system boundary used
• Confirm boundaries are consistent across all suppliers in comparison

Measured inputs (not model defaults)

• For methane leakage, source-specific data, not generic regional averages
• For electricity sourcing, look for PPA details, additionality evidence, and temporal matching
• For capture rate and configuration of blue pathways, assess what's captured and what isn't

Uncertainty and auditability

• Require uncertainty ranges alongside headline CI figures
• Require documentation that supports third-party audit

Contract terms

• Set CI thresholds with adjustment mechanisms if inputs change
• Define reporting frequency and change control triggers (e.g., if grid mix or gas sourcing changes)

What "Good" Looks Like in 2026

Leading hydrogen and ammonia producers are moving toward standardised CI calculation methodologies, verifiable sourcing claims supported by measured data, full documentation trails that support compliance and assurance, and comparable benchmarking across suppliers and regions.

For buyers and investors, "good" in 2026 means being able to compare CI across facilities using consistent standards. 

A colour label is not a proxy for verified performance — and in a market where the CI gap between same-coloured facilities can exceed 3x, treating it as one is a material risk.

Where Sylvera Stands

Sylvera has expanded beyond carbon credit ratings into carbon-differentiated commodity markets, providing independent CI assessment and market intelligence for hydrogen, ammonia, and other commodities. Here's how our tools support decision-making across pathways.

Carbon Intensity Assessment

Sylvera's Carbon Intensity Assessment provides an independent, third-party evaluation of facility-level CI data. Buyers and investors use our assessments to benchmark and compare hydrogen and ammonia producers with confidence. Our assessments also provide a clear documentation trail to support procurement decisions, ESG reporting, and compliance requirements.

Commodity Insights

Sylvera's Commodity Insights gives market participants live data and intelligence on supply, offtake dynamics, and CI performance across hydrogen and ammonia markets. For buyers, it protects against policy exposure and supports portfolio-level procurement strategy. For developers, it provides competitive positioning data and market signals to improve project success rates.

Need decision-grade carbon intensity benchmarking across hydrogen and ammonia pathways. Request a free demo of Sylvera today!

The Verdict on Green vs Blue Hydrogen Production

Colours are vague shorthand. Carbon intensity is the measurable truth. And the gap between the two — between what a label implies and what facility data shows — can be substantial enough to undermine procurement decisions, compliance positions, and investment theses built on colour alone.

If you're making procurement, investment, or development decisions in hydrogen and ammonia, require comparable CI methodologies, transparent assumptions, and auditable evidence. Then benchmark across suppliers using consistent standards to ensure accuracy.

The market is now moving toward standardised carbon intensity — where every kilogram of CO₂e improvement carries commercial value, and where facility-level data drives pricing the way quality ratings now drive price in the voluntary carbon market.

This is where Sylvera excels. Carbon Intensity Assessment and Commodity Insights help teams measure, compare, and act on CI with confidence. Request a demo.