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Hydrogen Colors and Carbon Intensity Explained

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TECHNOLOGY EXPLAINER

Hydrogen Colors and Carbon Intensity
— whose definition is "green", and over what boundary?

Terms such as "grey", "blue" and "green" hydrogen are widely used, but they are not terms defined in law or by an international standard. What national schemes actually use is the greenhouse gas emissions per kilogram of hydrogen (carbon intensity) and how those emissions are counted: from where to where, and which electricity is treated as renewable. Using official documents of the EU, Japan, the United States and international bodies as primary sources, this article sets out how the color names differ from the definitions in the schemes, and how carbon intensity is reasoned. Rules change, so the dates of checking are given. It is not legal, tax or investment advice.

Built from the Official Journal of the EU (directives and delegated regulations), Japan's e-Gov law database, the Basic Hydrogen Strategy, U.S. federal law and Treasury final rule, the IEA and ISO / Last updated 8 October 2026 (rules also checked on that date)

Conceptual hero image for Hydrogen Colors and Carbon Intensity
Conceptual image (AI-generated). An impression of two facilities that make hydrogen in different ways, one from electricity and one from natural gas, shown side by side. It does not show any real facility, product or layout, and does not indicate which color or scheme either would fall under.
Contents of this article
  1. What color-coding is (the short version)
  2. What the color names refer to — as informal usage
  3. A materials engineer's view (1): what a color hides
  4. Official definitions (1): the EU — RFNBO and low-carbon hydrogen
  5. Official definitions (2): Japan — the Basic Hydrogen Strategy and the Hydrogen Society Promotion Act
  6. Official definitions (3): the United States — 45V
  7. Official definitions (4): international bodies and standards — IEA and ISO
  8. Reading the schemes side by side — thresholds, and differences in boundary
  9. How carbon intensity is calculated — our calculation
  10. A materials engineer's view (2): do equipment materials count?
  11. Challenges, and what we could not confirm
  12. Glossary / References / Claim-to-source audit
How claims are labelled in this article

Sourced = stated in published material (link given)
Our calculation = a figure this article derived, with the assumptions spelled out
Not yet confirmed = a plan, target or item under review with no confirmed outcome
Structural readings are marked separately as Commentary, and weakly supported ideas are labelled Inference.
Rules are described by stage: proposal, adoption (enactment) and entry into force (application). The date of checking is 8 October 2026.

Scope of this article

This article is an explanation of schemes. It is not legal, tax or other advice on which scheme a particular project or transaction satisfies. The thresholds are transcribed from the text of each scheme's provisions or official documents. Schemes may be amended afterward, so check the original text and the latest position before any actual decision. Nor is it advice on handling or operating hydrogen.

1. What color-coding is (the short version)

Burning hydrogen produces no carbon dioxide, but the greenhouse gases emitted in making it vary greatly with the feedstock and the energy used. Color names have been used as shorthand for that difference.

  • Colors are informal: the IEA says there is no international agreement on the use of these terms (grey for production from unabated fossil fuels, blue for fossil fuels with carbon capture and storage, green for electrolysis using renewable electricity), and that existing definitions are generally considered insufficient to be used as a reference in regulations or supply contractsSourced [Reference 11].
  • What color does not say: the same report says "grey" and "blue" give no information about important factors such as upstream and midstream methane emissions and the carbon capture rate [Reference 11].
  • What schemes use: the EU, Japanese and U.S. schemes all distinguish hydrogen by an emissions threshold (kg-CO2e/kg-H2 and so on) and the way it is countedSourced [References 1–10].
The single most important line in this article

When asking "is it green hydrogen?", one also has to ask "by whose definition, counting emissions up to where, and which electricity is treated as renewable?" The same hydrogen can fall inside one scheme and outside another (Commentary).

2. What the color names refer to — as informal usage

NameWhat it generally refers toWhat it hides
GreyHydrogen made from fossil fuels such as natural gas without capturing CO2 (IEA wording: unabated fossil fuels)Upstream methane emissions; the type of fuel (natural gas or coal)
BlueHydrogen made from fossil fuels with CO2 captured and stored (IEA wording)Capture rate; upstream methane emissions; where the captured CO2 goes
GreenHydrogen made by electrolysis of water with renewable electricity (IEA wording)Which electricity counts as renewable (direct line or grid; annual or hourly)
Others (pink, turquoise and so on)Names that are sometimes used for electrolysis with nuclear power, methane pyrolysis and the likeWe could not confirm official definitions of these colors in the public sources we reviewed

The descriptions of grey, blue and green are the IEA's [Reference 11]. "Others" gives only examples of names, because we could not confirm official definitions. Japan's Basic Hydrogen Strategy does note that France's national strategy targets "decarbonised hydrogen", covering not only renewable-based hydrogen but also nuclear-based hydrogen [Reference 8].

The IEA also notes that colored terms do not handle actual operation where no color has been assigned, as when the electrolyzer runs on grid electricity (for example, much of today's electrolysis runs on grid power, for which no color has been proposed) [Reference 11].

3. A materials engineer's view (1): what a color hides

Color names and the variables behind them (our summary) Note: a color is a rough classification of how hydrogen is made; it does not fix the emissions. Grey Blue Green Variables that set emissions Feedstock type, upstream methane, reformer heat source, efficiency Variables that set emissions The above, plus CO₂ capture rate and emissions of capture, transport, storage Variables that set emissions Source of power (direct, grid), time matching, new or existing, efficiency Every scheme decides by an emissions threshold and a way of counting, not by color The same color can be judged differently if the boundary or the electricity conditions differ Note: the variables are our summary based on the IEA [11], the EU delegated regulations [2, 5] and the U.S. final rule [10].
Fig. 1 Conceptual diagram (vector drawing). A color name is a rough classification of how hydrogen is made; the variables that set emissions lie behind it. This is our own summary and not an official classification table.
A materials engineer's view: a color is a "label for how it is made", not a result

Materials offer similar cases: a name such as "high-strength steel" does not tell you the composition or heat treatment. A color name sits in the same position. The "performance value", emissions, is only fixed by the conditions of manufacture (feedstock, electricity, capture rate, boundary).

That is why, for a materials engineer, it matters that items governed by the performance of materials, catalysts and membranes, such as the electricity consumption of electrolysis (kWh/kg-H2), act on carbon intensity in proportion. Chapter 9 puts numbers on this (Commentary).

4. Official definitions (1): the EU — RFNBO and low-carbon hydrogen

The EU has two frameworks for distinguishing hydrogen: RFNBO (renewable fuels of non-biological origin) and low-carbon hydrogen.

(1) RFNBO — when electricity counts as "fully renewable"

  • The basic directive: Directive (EU) 2023/2413 (RED III, adopted 18 October 2023, published 31 October 2023) says energy from RFNBO counts toward Member States' renewable shares and targets only if the greenhouse gas emissions savings are at least 70% (Article 29a)Sourced [Reference 1]. It also contains provisions requiring RFNBO to be 42% of the hydrogen used in industry by 2030 and 60% by 2035 (Article 22a) [Reference 1].
  • Conditions for electricity: Delegated Regulation (EU) 2023/1184 (adopted 10 February 2023, published 20 June 2023) sets when electricity used in electrolysis counts as fully renewable. For electricity taken from the grid the principle is to meet: (1) additionality (the renewable installation came into operation no more than 36 months before the fuel installation and has received no operating or investment aid; Article 5); (2) temporal correlation (until 31 December 2029, the same calendar month; from 1 January 2030, the same one-hour period; Member States may apply this from 1 July 2027 after notification; Article 6); (3) geographical correlation (the same bidding zone and so on; Article 7) [Reference 2].
  • Exceptions and transition: there are separate provisions for bidding zones where the renewable share exceeded 90% in the previous year, zones with grid emission intensity below 18 gCO2eq/MJ, and electricity that avoids redispatching (Article 4). For installations that come into operation before 1 January 2028, the additionality requirements (Article 5(a) and (b)) do not apply until 1 January 2038 (Article 11). The Commission is to submit a report on impacts by 1 July 2028 (Article 10) [Reference 2].
  • Amendment: the regulation has been amended by Delegated Regulation (EU) 2024/1408 (dated 14 March 2024, published 21 May 2024). The consolidated EUR-Lex version (10 June 2024) titles the act as covering "renewable fuels of non-biological origin" [Reference 2]. We have not confirmed the content of that amendment.

(2) Calculating the emission savings — the fossil comparator of 94 g/MJ

Delegated Regulation (EU) 2023/1185 (same dates) sets the method of calculation of greenhouse gas savings for RFNBO and recycled carbon fuels and fixes the fossil fuel comparator at 94 gCO2eq/MJSourced [Reference 3]. The 70% savings threshold is therefore 94 × (1 − 0.70) = 28.2 gCO2eq/MJ; with a lower heating value for hydrogen of 120 MJ/kg (the value in Annex III of RED III [Reference 1]) this is about 3.38 kgCO2eq/kg-H2Our calculation. The method states that emissions from the manufacture of machinery and equipment are not taken into account [References 3, 5].

(3) Low-carbon hydrogen — fossil-based hydrogen can qualify if it meets the standard

  • Definition: Article 2(11) of Directive (EU) 2024/1788 (adopted 13 June 2024, published 15 July 2024) defines low-carbon hydrogen as hydrogen whose energy content is derived from non-renewable sources and which meets the 70% emissions reduction threshold against the fossil fuel comparator for RFNBOSourced [Reference 4]. The transposition deadline for Member States is 5 August 2026 according to the text [Reference 4].
  • Calculation method: Delegated Regulation (EU) 2025/2359 (adopted 8 July 2025, published 21 November 2025) sets the method for savings from low-carbon fuels other than recycled carbon fuels. The formula is E = ei + ep + etd + eu − eccs − eccu (supplied inputs, processing, transport and distribution, end-use combustion, and savings from CO2 capture and storage or use), and the savings are the ratio against the comparator [Reference 5]. It takes into account the actual CO2 capture rates and upstream methane emissions, and credits storage only in permitted geological storage (not used for enhanced oil and gas recovery) [Reference 5]. The global warming potential of hydrogen is not yet in the formula, because it has not been determined with the required precision [Reference 5].
  • Entry into force: the regulation enters into force on the twentieth day after publication; from the text we calculate that it entered into force on 11 December 2025Our calculation [Reference 5]. The Commission is to assess, by 1 July 2028, alternative pathways such as low-carbon electricity from nuclear power (Article 3)Not yet confirmed [Reference 5].
The EU stages (proposal, adoption, entry into force)

All of these documents are adopted and in force (RED III: Official Journal 31 October 2023; Delegated Regulations 2023/1184 and 2023/1185: 20 June 2023; Directive 2024/1788: 15 July 2024; Delegated Regulation 2025/2359: 21 November 2025). Each states that it enters into force on the twentieth day after publication, and the dates of entry into force are values we calculatedOur calculation. The future reviews (reports and assessments by 1 July 2028) are Not yet confirmed. As of the date of checking (8 October 2026), we could not confirm whether any amending proposals to these have been adopted.

5. Official definitions (2): Japan — the Basic Hydrogen Strategy and the Hydrogen Society Promotion Act

  • Basic Hydrogen Strategy (6 June 2023, Cabinet-level ministerial council on renewable energy and hydrogen): it sets as low-carbon hydrogen hydrogen for which CO2 emissions at "Well to Production Gate" are at most 3.4 kg-CO2e per kg. A footnote explains Well to Production Gate as "from feedstock production to the outlet of the hydrogen production equipment". Low-carbon ammonia is set at 0.84 kg-CO2e/kg-NH3 or less on a Gate to Gate basis (including hydrogen production)Sourced [Reference 8].
  • Future scope of calculation: the strategy says that, while aligning the scope with international standards, it will be necessary to evaluate also CO2 emitted by long-distance transport of hydrogen made abroad, conversion to carriers, and separation and recovery of hydrogen. It also says the definition is to be reviewed as technology progresses [Reference 8]. It states that carbon intensity will follow a methodology of the IPHE and that Japan will set a low-carbon target on a par with international levels [Reference 8].
  • Hydrogen Society Promotion Act: the "Act on Promotion of Supply and Use of Low-Carbon Hydrogen etc. for Smooth Transition to a Decarbonized Growth-Oriented Economic Structure" (Act No. 37 of Reiwa 6) was promulgated on 24 May 2024 and entered into force on 23 October 2024Sourced [Reference 6]. Article 2 defines low-carbon hydrogen etc. as those meeting requirements set by ministerial ordinance of the Ministry of Economy, Trade and Industry (METI), including that CO2 emitted in production is at or below a certain value [Reference 6].
  • Enforcement Regulation (METI Ordinance No. 69 of Reiwa 6, promulgated and in force 23 October 2024): Article 3 sets, for hydrogen, CO2 (other greenhouse gases converted by global warming potential) of at most 3.4 kg per kg of hydrogen produced; for ammonia, at most 0.87 kg per kg; for synthetic fuels, at most 39.9 g per MJ (emissions of production, transport, storage and use, less CO2 captured for use as feedstock); and for synthetic methane, at most 49.3 g/MJ. The calculation method is set by the Minister of Economy, Trade and Industry (Article 3, paragraph 5)Sourced [Reference 7].
  • Support focused on the price gap: under the Act, the competent minister certifies a plan prepared jointly by a supplier and a user (Article 7), and the Japan Organization for Metals and Energy Security (JOGMEC) pays subsidies for the funds a certified supplier needs to keep supplying low-carbon hydrogen etc. (Article 10). The certification criteria include that the plan is economic and reasonable, and that supply starts by a set fiscal year and continues for at least the period set by ministerial ordinance [Reference 6].
Note: the strategy and the ordinance give different ammonia values

Low-carbon ammonia is given as 0.84 in the Basic Hydrogen Strategy (June 2023) and 0.87 kg-CO2/kg-NH3 in the Enforcement Regulation (October 2024) [References 7, 8]. The nature of the documents (strategy or law) and their dates differ. The legal requirement is the ordinance's value, but we could not confirm the reason for the difference. Also, we could not confirm the text of the calculation method set by the Minister or the number and content of certified plans (as of 8 October 2026).

6. Official definitions (3): the United States — 45V

  • Basis: the Inflation Reduction Act of 2022 (Pub. L. 117-169, 16 August 2022) added §45V to the Internal Revenue CodeSourced [Reference 9].
  • Emissions tiers and credit: hydrogen with a lifecycle greenhouse gas emissions rate of at most 4 kg-CO2e per kg is "qualified clean hydrogen", and the base amount of $0.60 is multiplied by an applicable percentage: 20% for 2.5–4 kg, 25% for 1.5 to under 2.5 kg, 33.4% for 0.45 to under 1.5 kg, and 100% for under 0.45 kg (facilities meeting wage and apprenticeship requirements get 5 times that). The base amount is adjusted for inflationSourced [Reference 9].
  • Scope of calculation: lifecycle emissions are counted through the point of production (well-to-gate) using the GREET model of Argonne National Laboratory (or a successor). The hydrogen must be produced in the United States and production and sale or use verified by an unrelated party [Reference 9].
  • Time limit: the credit runs for 10 years from the facility's placed-in-service date, and construction must begin before 1 January 2028. That date was brought forward from 1 January 2033 by the law of 4 July 2025 (Pub. L. 119-21 §70511)Sourced [Reference 9].
  • Relation to 45Q: no 45V credit is allowed for hydrogen produced at a facility that includes carbon capture equipment for which a 45Q (carbon oxide sequestration) credit is allowed (§45V(d)(2)) [Reference 9].
  • Treasury final rule (90 FR 2224, published and effective 10 January 2025): for electricity, it sets conditions on energy attribute certificates (EACs) matched to the electricity used by the hydrogen facility: incrementality (the generator's commercial operation date is within 36 months of the hydrogen facility's placed-in-service date; for an existing fossil plant with CCS, the CCS equipment's date is used), temporal matching (the same hour from 1 January 2030; the same calendar year before then) and deliverability (the same region, judged by the balancing authority to which each is interconnected)Sourced [Reference 10].
Our calculation: converting the credit amounts

From the figures in the statute, the credit per kg when the wage and apprenticeship requirements are met (before inflation adjustment)Our calculation.

  • Under 0.45 kg: 0.60 × 100% × 5 = US$3.00/kg
  • 0.45 to under 1.5 kg: 0.60 × 33.4% = 0.2004, rounded to the nearest 0.1 cent = 0.200, × 5 = US$1.00/kg
  • 1.5 to under 2.5 kg: 0.60 × 25% × 5 = US$0.75/kg; 2.5–4 kg: 0.60 × 20% × 5 = US$0.60/kg

Assumptions and limits: the base amount is adjusted for inflation, so actual amounts change by year. Without meeting the wage and apprenticeship requirements the 5-times factor does not apply. We could not confirm whether the January 2025 final rule was amended after the July 2025 change in the law (as of 8 October 2026).

7. Official definitions (4): international bodies and standards — IEA and ISO

  • IEA (2023 report for the G7): it says colors and terms such as "sustainable", "low-carbon" or "clean" are hard to use as a basis for contracts, and that governments adopting definitions based on the emissions intensity of hydrogen production in their regulations would improve interoperability of markets and regulation. The report gives no generic acceptable upper limit, leaving each country to set its level according to its circumstancesSourced [Reference 11].
  • IPHE methodology: the IEA report treats electrolysis on renewable electricity as 0 kg-CO2e/kg-H2 under the IPHE methodology, which assigns no emissions to renewable power generation [Reference 11].
  • ISO: the ISO page states that ISO/TS 19870:2023 will be replaced by ISO 19870-1:2026, "Hydrogen technologies — Methodology for determining the greenhouse gas emissions associated with the hydrogen supply chain — Part 1: Emissions associated with the production of hydrogen up to the production gate" (published April 2026). It deals with a partial carbon footprint up to the production gateSourced [Reference 13]. The full text is paid, so this article stays with the title and the stated scope.
  • The situation in 2025 (IEA): world hydrogen demand was almost 100 million tonnes in 2024, and the use of low-emissions hydrogen was under 1% of the total [Reference 12].

8. Reading the schemes side by side — thresholds, and differences in boundary

SchemeNameThreshold (hydrogen)BoundaryElectricity conditions (electrolysis)Stage
EU RFNBORenewable fuels of non-biological origin70% off 94 g/MJ = 28.2 g/MJ (≈3.38 kg/kg, our calculation)Formula ei+ep+etd+eu−… (includes transport and distribution). Equipment manufacture excludedAdditionality, time and geographic correlation (calendar month, then one hour from 2030) etc.In force (Delegated Regulations 2023/1184, 1185)
EU low-carbon hydrogenLow-carbon hydrogenSame 70% reduction (RFNBO comparator)Same (credits CCS, upstream methane, actual capture rate)Consistency rules with RFNBO hydrogen on time period, etc.Directive: transposition deadline 5 August 2026; Delegated Regulation 2025/2359 in force
JapanLow-carbon hydrogen etc.At most 3.4 kg-CO2e/kg-H2 (ordinance)Feedstock production to outlet of production equipment (strategy). Calculation method set by the Minister (ordinance)Could not be confirmedAct and ordinance in force from 23 October 2024
U.S. 45VQualified clean hydrogenTiered, up to 4 kg (0.45 / 1.5 / 2.5 / 4 kg)Through the point of production (well-to-gate), GREET modelEAC: new within 36 months, same region, hourly from 2030In force. Construction must begin before 1 January 2028 (shortened July 2025)
InternationalIEA / ISOThe IEA gives no generic ceilingISO 19870-1: up to the production gate—ISO 19870-1 published April 2026

The sources are the references of chapters 4 to 7. Because the boundaries are not the same, the threshold numbers cannot be ranked directly. The EU "3.38" is our calculation (94 g/MJ × 30% × 120 MJ/kg), not a number in the text of the regulation.

How far each scheme counts emissions (our summary) Note: a concept diagram based on each scheme's documents. Check the original text for details. Feedstock, upstream Hydrogen production Transport, distribution Use U.S. 45V Up to the point of production Japan Up to the outlet of the equipment ISO 19870-1 Up to the production gate EU Formula includes transport and distribution (e_td) and use (e_u). Hydrogen combustion is 0 With a different boundary, the same hydrogen gets a different number. Read a threshold with its boundary Japan says it must also evaluate transport, carrier conversion and separation emissions in future [8] Note: based on 45V [9], the Japanese strategy [8], ISO page [13], EU formula [3, 5]. Length shows breadth, not emissions.
Fig. 2 Conceptual diagram (vector drawing). The boundary of emissions counted differs by scheme. Details of each scheme (upstream methane, how electricity is counted and so on) are omitted; the figure is a guide to breadth of boundary.
Emission intensity of production routes (IEA) and scheme thresholds (our summary) Unit: kg-CO₂e/kg-H₂. Bars are IEA (2023) ranges; the dashed line is a scheme threshold 100% 33.4% 25% 20% ← Japan 3.4 / EU about 3.38 (our conversion) ← Shaded bands are the U.S. 45V tiers: 0.45 / 1.5 / 2.5 / 4 Renewable electrolysis (IPHE) Natural gas + capture over 90% Natural gas + capture about 60% Natural gas (no capture) 0 0.8 to 6 5 to 8 10 to 14 Note: the axis is proportional, 0 to 14 kg-CO₂e/kg-H₂. The IEA notes no plant above 90% capture was operating then. Note: ranges from the IEA [11]; thresholds from the EU [3, 5], Japan [7] and the U.S. [9]. The IEA gives no generic acceptable ceiling. Note: the spread is mainly upstream and midstream methane (1 to 5 kg). Boundaries differ, so comparison is a guide.
Fig. 3 Conceptual diagram (vector drawing). Bars are the ranges in the IEA report [Reference 11]; the dashed line is a threshold of the schemes. The EU figure of about 3.38 is our conversion, and because boundaries differ by scheme, the relative size of thresholds is a guide.

9. How carbon intensity is calculated — our calculation

Carbon intensity is total emissions ÷ the amount of hydrogen produced. The unit is kg-CO2e/kg-H2 in Japan and the United States and g-CO2eq/MJ in the EU. Conversion uses the lower heating value of hydrogen, 120 MJ/kg (the RED III Annex III value [Reference 1]). The calculations below aim at grasping orders of magnitude, with every assumption written down; they do not assess the emissions of any particular project.

(1) Converting thresholds

Our calculation

Our calculation

  • EU (RFNBO and low-carbon hydrogen): 94 g/MJ × (1 − 0.70) = 28.2 g/MJ. × 120 MJ/kg = 3,384 g = about 3.38 kg-CO2e/kg-H2
  • Japan: 3.4 kg ÷ 120 MJ/kg = 0.02833 kg/MJ = about 28.3 g/MJ
  • U.S. 45V, upper limit of the lowest tier: 4.0 kg ÷ 120 MJ/kg = about 33.3 g/MJ

Assumptions and limits: that the numbers are close (EU 28.2, Japan 28.3 g/MJ) can be read as reflecting Japan's aim at a level on a par with international ones (the strategy's wording [Reference 8]), but we have not found a document saying Japan adopted the EU value (Inference). Because the boundaries differ (Fig. 2), one cannot say which threshold is stricter by comparing the numbers directly.

(2) Electrolysis carbon intensity is electricity consumption × the emission factor of the electricity

Our calculation

The carbon intensity of electrolytic hydrogen is approximately as followsOur calculation.

  • Formula: CI = electricity consumption (kWh/kg-H2) × emission factor of electricity (g/kWh) ÷ 1,000
  • Assumed consumption: the DOE PEM system status (2022) of 55 kWh/kg (61% LHV), 51 as the 2026 target and 46 as the ultimate target [Reference 14]
  • Electricity emission factor that stays within each threshold (break-even): threshold ÷ 55 kWh/kg
    • EU 3.38 kg → about 61.5 g/kWh; Japan 3.4 kg → about 61.8 g/kWh
    • U.S. 4.0 kg → about 72.7 g/kWh; 2.5 kg → about 45.5; 1.5 kg → about 27.3; 0.45 kg → about 8.2 g/kWh
  • Effect of improving consumption: 55 → 51 kWh/kg is 1 − 51/55 = about 7.3% lower; 55 → 46 is 1 − 46/55 = about 16.4% lower (carbon intensity falls by the same proportion for the same electricity emission factor)

Assumptions and limits: emissions other than electricity (water, equipment manufacture, auxiliaries) are not counted, and all electricity is assumed to have one emission factor. The actual EU and U.S. schemes judge not by the grid average emission factor but by conditions for procuring renewable electricity (additionality, time, region), so this is not as simple as "use electricity below the threshold". The DOE values are targets and status values, not the performance of any particular unit.

Electricity emission factor that stays within each threshold (our calculation) Assumes 55 kWh/kg-H₂ for electrolysis (DOE PEM system status, 2022). Unit: g-CO₂/kWh U.S. 45V: up to 4.0 kg (20%) Japan: up to 3.4 kg EU: about 3.38 kg (70% savings) U.S. 45V: under 2.5 kg (25%) U.S. 45V: under 1.5 kg (33.4%) U.S. 45V: under 0.45 kg (100%) 72.7 61.8 61.5 45.5 27.3 8.2 Note: threshold ÷ 55 kWh/kg; bar length is proportional. Non-electricity emissions are not counted. Real schemes differ.
Fig. 4 Chart containing our calculation (vector drawing). Thresholds are from the EU [References 3, 5], Japan [Reference 7] and the U.S. [Reference 9], and consumption is from DOE [Reference 14]. The values in the chart (g/kWh) were derived in this article and are not published values.

(3) Natural gas reforming with CO2 capture — how the capture rate acts

Our calculation

The IEA (2023) puts the emissions intensity of natural-gas-based hydrogen without CO2 capture at 10 to 14 kg-CO2e/kg-H2, of which upstream and midstream methane and CO2 emissions are 1 to 5 kgSourced [Reference 11]. From this difference we can set direct emissions D = 10 − 1 = 14 − 5 = 9 kg (both ends give the same value)Our calculation. With an assumed capture rate η (the share of direct emissions captured), CI = (1 − η) × 9 + U, where U is the upstream and midstream emissions.

For reference, the reaction CH4 + 2H2O → CO2 + 4H2 gives, per 1 kg of hydrogen (≈496 mol), CO2 of ≈124 mol = about 5.46 kg from the feedstock alone (the emissions of the reformer heat source are separate)Our calculation.

Threshold (kg-CO2e/kg-H2)Required η at U = 1 kgU = 2 kgU = 3 kgU = 4 kg
3.4 (Japan) / about 3.38 (EU)about 73%about 84%about 96%exceeded even at 100%
4.0 (upper limit for U.S. 45V eligibility)about 67%about 78%about 89%100% (exactly)
2.5 (upper limit of the 25% tier of U.S. 45V)about 83%about 94%not reachablenot reachable

Assumptions and limits: D = 9 kg is back-calculated from the IEA's range and is not a value for any individual plant. The emissions of capture operations, transport and storage (eCO2-c, eCO2-t and eCO2-i in the EU formula) are not part of η and must be deducted separately [Reference 5]. The IEA gives 5 to 8 kg at a capture rate of about 60% and 0.8 to 6 kg above 90%, and records that plants achieving over 90% were not operating at the time (2023) [Reference 11]. "Not reachable" and "exceeded" in the table show that when upstream emissions are large, the capture rate alone cannot reach the threshold (Commentary). Capture itself is covered in our CCS explainer.

10. A materials engineer's view (2): do equipment materials count?

Conceptual supporting image for Hydrogen Colors and Carbon Intensity
Fig. 5 Conceptual image (AI-generated). An impression of confirming and recording, by meter, the electricity used and the hydrogen produced. It does not show any real facility, meter or procedure, and does not depict the procedure of any specific certification scheme.
A materials engineer's view: the "performance" of materials counts, but the "manufacture" of materials does not

In the calculations of the schemes seen so far, items related to equipment materials are handled as follows.

  • Emissions from manufacturing equipment are not counted. Both EU delegated regulations state that "emissions from the manufacture of machinery and equipment shall not be taken into account"Sourced [References 3, 5]. The emissions from making the materials of an electrolyzer, such as iridium, platinum, titanium and PFSA membranes, therefore do not appear in this calculation. IRENA, in a different context, says platinum production dominates almost all environmental impact categories [Reference 15].
  • The "performance" of materials enters through electricity consumption. The carbon intensity of electrolysis is proportional to electricity consumption (chapter 9). Membrane thickness, catalyst activity and the contact resistance of bipolar plates affect cell voltage, that is kWh/kg, and so act on carbon intensity in proportion (Commentary).
  • Degradation worsens carbon intensity over time. DOE defines the end of life as a 10% rise from the initial voltage [Reference 14]. If the voltage rise passed straight through to electricity consumption, carbon intensity at end of life would be about 10% higher, and to stay under the 3.4 kg threshold the initial intensity would have to be at most 3.4 ÷ 1.10 = about 3.09 kg (about 56 g/kWh of electricity at the 55 kWh/kg above)Our calculation. In practice auxiliary power does not degrade, so the rise would be smaller (degradation of the stack is covered in our explainer on electrolyzer stacks and materials).
  • Hydrogen leakage is not yet counted. The EU's 2025 delegated regulation says the global warming potential of hydrogen has not yet been determined with the required precision, so it is left out of the formula [Reference 5]. The performance of sealing and barrier materials (our explainer on barrier properties and coatings) may come to bear on carbon intensity accounting in future, but it is not in the current formula (Commentary).

In short: in the debate on colors and carbon intensity, materials appear mainly as electricity consumption (efficiency) and lifetime (degradation) (Commentary).

11. Challenges, and what we could not confirm

Main challenges
  • Boundaries are not harmonized: the EU counts through transport and distribution; Japan, the United States and ISO count up to the production gate, so thresholds cannot be ranked [References 3, 5, 8, 9, 13]
  • How electricity is counted: the EU (additionality, time, geography) and the United States (new EACs, time, region) take similar approaches, but details and transitional provisions differ [References 2, 10]
  • Rules are changing: the U.S. construction deadline was shortened in July 2025, and the EU plans a reassessment in 2028 [References 5, 9]
  • Leakage and methane: the treatment of hydrogen's warming potential and of upstream methane is still developing [References 5, 11]

(1) We could not confirm the text of Japan's calculation method or the record of certifications

The Enforcement Regulation says the CO2 quantity is calculated by a method set by the Minister of Economy, Trade and Industry, but we could not confirm the text of that method. Nor could we confirm the number and content of certified plans for price-gap support (as of 8 October 2026).

(2) We could not confirm later amendments to the U.S. final rule

We could not confirm whether the Treasury final rule of January 2025 was amended or withdrawn after the July 2025 change in the law. Check the latest Federal Register to see whether the electricity conditions (additionality, time, region) are still the same.

(3) We could not confirm developments in EU amending proposals

For the RFNBO electricity conditions (Delegated Regulation 2023/1184), we could not confirm the content of the 2024 amendment (2024/1408), or whether any further amending proposals have been adopted up to 8 October 2026.

(4) Other countries and certification schemes are not covered

The schemes of the United Kingdom, Korea, China and others, private certification schemes and the full text of the IPHE methodology are not covered. We also could not confirm official definitions of color names such as pink and turquoise.

(5) Actual carbon intensity records are not covered

We could not confirm in primary sources measured or certified carbon intensity values for individual projects, so none are given. The calculations in chapter 9 are orders of magnitude based on assumptions.

Summary of this article
  • Colors are informal and have no internationally agreed definition. Schemes decide by an emissions threshold and a way of countingSourced
  • The EU takes 70% off the 94 g/MJ fossil comparator (28.2 g/MJ, ≈3.38 kg/kg). Japan sets at most 3.4 kg-CO2e/kg-H2. The United States gives four tiers up to 4 kgSourced / Our calculation
  • The boundaries differ. The United States, Japan and ISO count up to production, while the EU includes transport and distributionSourced
  • The carbon intensity of electrolysis is consumption × the electricity emission factor. At 55 kWh/kg, the emission factor that stays within 3.4 kg is about 62 g/kWhOur calculation
  • For natural gas with CCS, upstream methane matters as much as the capture rate. With upstream emissions of 3 kg, the capture rate needed for a 3.4 kg threshold is about 96%Our calculation
  • Materials act on carbon intensity through electricity consumption and degradation. The emissions of manufacturing equipment are not in the EU formulaSourced

12. Glossary

Carbon intensity (CI)
Greenhouse gas emissions per unit of product. For hydrogen, kg-CO₂e/kg-H₂ or g-CO₂eq/MJ.
CO₂e (CO₂ equivalent)
The amount of other greenhouse gases converted to CO₂ by global warming potential.
RFNBO
Renewable fuels of non-biological origin, such as hydrogen made from renewable electricity. An EU term.
Additionality
The condition that electricity comes from renewable installations newly built for the hydrogen.
Temporal correlation
The condition that the time hydrogen is made matches the time the renewable power was generated (calendar month, one hour and so on).
EAC
Energy attribute certificate. A certificate of the environmental attributes of electricity, used in U.S. 45V.
Well-to-gate
From extraction of the feedstock to the gate (outlet) of the production facility. Transport and use are not included.
45V
The section of the U.S. Internal Revenue Code giving a tax credit for clean hydrogen production.
GREET model
The lifecycle emissions model of Argonne National Laboratory in the United States.
Lower heating value (LHV)
Heating value of a fuel excluding the heat of condensation of water vapor. About 120 MJ/kg for hydrogen.
IPHE
The International Partnership for Hydrogen and Fuel Cells in the Economy. It has published an emissions calculation methodology.
Capture rate
The share of emitted CO₂ that is captured. Its meaning changes with which emissions form the denominator.

13. References

  1. European Parliament and Council Directive (EU) 2023/2413 (RED III), 18 October 2023, Official Journal 31 October 2023 — eur-lex.europa.eu
  2. European Commission Delegated Regulation (EU) 2023/1184 (detailed rules for RFNBO electricity), 10 February 2023, Official Journal 20 June 2023 (amended by Delegated Regulation (EU) 2024/1408) — eur-lex.europa.eu
  3. European Commission Delegated Regulation (EU) 2023/1185 (methodology for savings of RFNBO and recycled carbon fuels), 10 February 2023, Official Journal 20 June 2023 — eur-lex.europa.eu
  4. European Parliament and Council Directive (EU) 2024/1788 (internal markets for renewable gas, natural gas and hydrogen), 13 June 2024, Official Journal 15 July 2024 — eur-lex.europa.eu
  5. European Commission Delegated Regulation (EU) 2025/2359 (methodology for savings of low-carbon fuels), 8 July 2025, Official Journal 21 November 2025 — eur-lex.europa.eu
  6. Japan Act on Promotion of Supply and Use of Low-Carbon Hydrogen etc. for Smooth Transition to a Decarbonized Growth-Oriented Economic Structure (Act No. 37 of Reiwa 6; in Japanese), promulgated 24 May 2024, in force 23 October 2024 (e-Gov Law Search) — laws.e-gov.go.jp
  7. Ministry of Economy, Trade and Industry Enforcement Regulation of the same Act (METI Ordinance No. 69 of Reiwa 6; in Japanese), promulgated and in force 23 October 2024 (e-Gov Law Search) — laws.e-gov.go.jp
  8. Cabinet-level Ministerial Council on Renewable Energy and Hydrogen "Basic Hydrogen Strategy" (in Japanese), 6 June 2023 (PDF) — meti.go.jp
  9. United States 26 U.S. Code § 45V (credit for production of clean hydrogen), amended by Pub. L. 117-169 §13204 (16 August 2022) and Pub. L. 119-21 §70511 (4 July 2025) — law.cornell.edu
  10. U.S. Department of the Treasury and Internal Revenue Service Final rule "Credit for Production of Clean Hydrogen and Energy Credit", 90 FR 2224, published and effective 10 January 2025 — federalregister.gov
  11. International Energy Agency (IEA) "Towards hydrogen definitions based on their emissions intensity" (2023, for the G7) — iea.org
  12. International Energy Agency (IEA) "Global Hydrogen Review 2025" (revised October 2025) — iea.org
  13. ISO "ISO 19870-1:2026 Hydrogen technologies — Methodology for determining the greenhouse gas emissions associated with the hydrogen supply chain — Part 1: Emissions associated with the production of hydrogen up to the production gate" (published April 2026; title and scope only, the full text is paid) — committee.iso.org
  14. U.S. Department of Energy (DOE) "Technical Targets for Proton Exchange Membrane Electrolysis" (accessed 5 October 2026) — energy.gov
  15. IRENA "Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5°C Climate Goal" (December 2020) — irena.org

14. Claim-to-source audit

Claim in the textBasisLabel
RED III: RFNBO energy counts toward targets only with savings of at least 70% (Article 29a); RFNBO at 42% of industrial hydrogen by 2030 and 60% by 2035 (Article 22a); hydrogen heating value 120 MJ/kg (Annex III). Adopted 18 October 2023, Official Journal 31 October 2023Directive (EU) 2023/2413[Reference 1] https://eur-lex.europa.eu/eli/dir/2023/2413/ojSourced
Delegated Regulation 2023/1184: conditions for counting grid electricity as fully renewable (exceptions in Article 4; additionality of 36 months and no support in Article 5; temporal correlation in Article 6: calendar month until 31 December 2029, one hour from 1 January 2030, Member States may apply from 1 July 2027; geographical correlation in Article 7), the 1 July 2028 report in Article 10, the transitional rule in Article 11 (installations operating before 1 January 2028 exempt from Article 5(a)(b) until 1 January 2038). Adopted 10 February 2023, Official Journal 20 June 2023. Amended by Delegated Regulation 2024/1408 (consolidated version 10 June 2024)Delegated Regulation (EU) 2023/1184[Reference 2] https://eur-lex.europa.eu/eli/reg_del/2023/1184/ojSourced
Delegated Regulation 2023/1185: fossil fuel comparator 94 gCO2eq/MJ, 70% threshold for recycled carbon fuels, savings formula (EF − E)/EF, formula terms (e_i, e_p, e_td, e_u, e_ccs), emissions from manufacture of machinery and equipment not taken into accountDelegated Regulation (EU) 2023/1185[Reference 3] https://eur-lex.europa.eu/eli/reg_del/2023/1185/ojSourced
Directive 2024/1788 Article 2(11): definition of low-carbon hydrogen (from non-renewable sources, 70% reduction against the RFNBO comparator). Transposition by 5 August 2026 (Articles 2 to 6, 8 to 31 and others). Article 9 certification of low-carbon fuels (at least 70%, mass balance). Adopted 13 June 2024, Official Journal 15 July 2024Directive (EU) 2024/1788[Reference 4] https://eur-lex.europa.eu/eli/dir/2024/1788/ojSourced
Delegated Regulation 2025/2359: the formula E = e_i + e_p + e_td + e_u − e_ccs − e_ccu, the same comparator as 2023/1185, consideration of actual capture rate and upstream methane, crediting only permitted geological storage not used for enhanced recovery, equipment manufacture not counted, that the warming potential of hydrogen is not yet in the formula, Article 3 (assessment by 1 July 2028), the provision on installations operating before 11 December 2025. Adopted 8 July 2025, Official Journal 21 November 2025Delegated Regulation (EU) 2025/2359[Reference 5] https://eur-lex.europa.eu/eli/reg_del/2025/2359/ojSourced
Hydrogen Society Promotion Act: Act No. 37 of Reiwa 6, promulgated 24 May 2024, in force 23 October 2024. Article 2 (definition of low-carbon hydrogen etc. and delegation to ministerial ordinance), Article 7 (criteria for certifying plans), Article 10 (JOGMEC subsidies)e-Gov Law Search (Act)[Reference 6] https://laws.e-gov.go.jp/law/506AC0000000037Sourced
Enforcement Regulation Article 3: at most 3.4 kg per kg for hydrogen, at most 0.87 kg for ammonia, at most 39.9 g/MJ for synthetic fuels, at most 49.3 g/MJ for synthetic methane. The calculation method is set by the Minister of Economy, Trade and Industry. METI Ordinance No. 69 of Reiwa 6, promulgated and in force 23 October 2024e-Gov Law Search (ordinance)[Reference 7] https://laws.e-gov.go.jp/law/506M60000400069Sourced
Basic Hydrogen Strategy (6 June 2023): low-carbon hydrogen as at most 3.4 kg-CO2e at Well to Production Gate, with the footnote "from feedstock production to the outlet of the hydrogen production equipment"; low-carbon ammonia at most 0.84 kg-CO2e/kg-NH3 on a Gate to Gate basis; future evaluation of the calculation scope; review of the definition; IPHE methodology; reference to the IEA report; that France's national strategy also covers nuclear-based hydrogenBasic Hydrogen Strategy[Reference 8] https://www.meti.go.jp/shingikai/enecho/shoene_shinene/suiso_seisaku/pdf/20230606_2.pdfSourced
26 U.S.C. §45V: qualified clean hydrogen up to 4 kg, applicable percentages (20%, 25%, 33.4%, 100%), base amount $0.60, five times for wage and apprenticeship requirements, well-to-gate and GREET, U.S. production and third-party verification, construction deadline (before 1 January 2028, shortened from 2033 by Pub. L. 119-21 §70511), 10 years, no combination with 45Q, enacted 16 August 202226 U.S.C. §45V[Reference 9] https://www.law.cornell.edu/uscode/text/26/45VSourced
Treasury final rule 90 FR 2224: published and effective 10 January 2025. EAC incrementality (generator's commercial operation within 36 months of the hydrogen facility's placed-in-service date, with a special rule for CCS-equipped plants), temporal matching (same hour from 1 January 2030, same calendar year before), deliverability (same region). Calculation by the 45VH2-GREET model, annual and, from 2030, hourly accountingTreasury and IRS final rule[Reference 10] https://www.federalregister.gov/documents/2025/01/10/2024-31513/credit-for-production-of-clean-hydrogen-and-energy-creditSourced
IEA (2023): no international agreement on color terms, which are insufficient for regulation and contracts; examples of grey, blue and green; the proposal for emissions-intensity-based definitions and no generic ceiling; natural gas without capture 10 to 14, upstream and midstream 1 to 5, about 5 to 8 at about 60% capture, 0.8 to 6 above 90% (no plant operating then), 12 to 13 as the 2021 world average, renewable electrolysis 0 under the IPHE methodologyIEA report[Reference 11] https://www.iea.org/reports/towards-hydrogen-definitions-based-on-their-emissions-intensitySourced
World hydrogen demand of almost 100 million tonnes in 2024, with low-emissions hydrogen use under 1%IEA Global Hydrogen Review 2025[Reference 12] https://www.iea.org/reports/global-hydrogen-review-2025Sourced
Title of ISO 19870-1:2026, published April 2026, replacing ISO/TS 19870:2023, a partial carbon footprint up to the production gateISO standard page[Reference 13] https://committee.iso.org/standard/19870-1Sourced
DOE PEM electrolysis system energy efficiency: 55 kWh/kg (61% LHV) as 2022 status, 51 as the 2026 target, 46 as the ultimate target. End of life defined as a 10% rise from initial voltageDOE technical target table (PEM electrolysis)[Reference 14] https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysisSourced
The statement that platinum production dominates almost all environmental impact categories (citing Duclos et al.)IRENA (2020)[Reference 15] https://www.irena.org/Publications/2020/Dec/Green-hydrogen-cost-reductionSourced
Conversion of EU thresholds (94 × 0.30 = 28.2 g/MJ, × 120 = about 3.38 kg). Japan 3.4 kg ÷ 120 = about 28.3 g/MJ. U.S. 4.0 kg ÷ 120 = about 33.3 g/MJ. 45V credit amounts (US$3.00, 1.00, 0.75, 0.60 per kg, before inflation adjustment). Break-even electricity emission factors (3.38/55 = 61.5, 3.4/55 = 61.8, 4.0/55 = 72.7, 2.5/55 = 45.5, 1.5/55 = 27.3, 0.45/55 = 8.2 g/kWh). Consumption improvements (7.3%, 16.4%). Direct emissions D = 9 kg, CI = (1−η)×9 + U, and the table of required capture rates. About 5.46 kg CO2 from the reaction equation. The end-of-life allowance if a 10% voltage rise raises carbon intensity about 10% (3.4÷1.10 = about 3.09 kg, about 56 g/kWh). EU dates of entry into force (twentieth day after publication)Our calculation. Emissions other than electricity are not counted and all electricity is assumed to have one emission factor. D = 9 kg is back-calculated from the IEA range and is not a value for any individual plant. Boundaries differ by scheme, so this is not a ranking of thresholds. The 45V amounts are before inflation adjustment and assume the wage and apprenticeship requirements are metOur calculation
The Commission's assessment of alternative pathways in the EU Delegated Regulation 2025/2359 by 1 July 2028, the 2028 impact report for RFNBO, and future amendments in the United States, the EU and JapanPlans and reviews, with no confirmed adoption or implementation. An outlookNot yet confirmed
The text of the calculation method set by Japan's Minister, the number and content of certified plans, whether the U.S. final rule was amended after July 2025, whether further EU amending proposals exist, other countries' schemes and private certification, official definitions of colors such as pink and turquoise, and actual carbon intensity of individual projectsCould not be confirmed in primary sources within the scope of our survey, so not stated (as of 8 October 2026)Commentary
The framing that a color is a "label for how it is made" and does not fix emissions. The reading that thresholds cannot be compared directly because the boundaries differ. The framing that materials act on carbon intensity through electricity consumption and degradation. The reading that the Japanese and EU numbers are close (inference)Our organization and commentary based on published content. Not views stated by any institutionCommentary
That Figs. 1, 2, 3 and 4 are explanatory drawings, and that the hero image and Fig. 5 are AI-generated imagesOur noteCommentary

Last updated: 8 October 2026 (rules were checked on the same date). Sources are limited to primary material (the Official Journal of the EU, e-Gov Law Search, the Basic Hydrogen Strategy, U.S. federal law and the Federal Register, the IEA, and the ISO page). Because the article includes structural readings, those are marked as Commentary and kept separate from sourced fact. The text of Japan's calculation method, the record of certifications, any later amendment of the U.S. final rule, further EU amending proposals, and actual carbon intensity of individual projects could not be confirmed in primary sources and are therefore not stated. Rules are amended, so check the original text and the latest position before any actual decision; this article is not legal, tax or investment advice. All figures are explanatory concept graphics. Figs. 1 to 4 are vector drawings; the hero image and Fig. 5 are AI-generated images, and none of them shows a real facility or certification procedure.

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