IPCC AR6 Global Warming Potential Values

What Global Warming Potential measures

Global Warming Potential is the time-integrated radiative forcing of one mass unit of a greenhouse gas relative to one mass unit of carbon dioxide, evaluated over a specified time horizon. CO₂ is the reference: GWP(CO₂) = 1 by definition at every horizon. Every other greenhouse gas is expressed as a multiple. Methane at GWP-100 of 29.8 means one tonne of methane (fossil origin) traps 29.8 times more cumulative energy in the atmosphere than one tonne of CO₂ over a 100-year window.

The time horizon is not a precision setting — it is a policy choice with material consequences. GWP-20 weights short-term warming heavily; GWP-100 weights long-term cumulative forcing; GWP-500 captures multi-century persistence. For methane, with an atmospheric lifetime of approximately 11.8 years, the GWP-20 value (82.5) is roughly 2.8 times the GWP-100 value (29.8) because at 20 years most of the methane molecule’s warming capacity is still being expressed. By the 100-year mark, most has oxidised to CO₂ and water vapour, so the time-integrated impact per unit emission is proportionally smaller.

Feedback vs no-feedback — the AR6 distinction that matters

IPCC AR6 introduced a refinement that earlier assessments did not present consistently: the explicit distinction between GWP values calculated with and without climate-carbon cycle feedbacks. This distinction has practical consequences for every CO₂e calculation downstream.

Climate-carbon feedbacks are secondary effects triggered by the warming caused by a greenhouse gas. Warming weakens the ocean and terrestrial carbon sinks, accelerates permafrost thaw, and modifies the residence time of CO₂ itself in the atmosphere. These secondary effects amplify the radiative forcing attributable to a unit emission. Including them produces slightly higher GWP values; excluding them produces the conventional values.

For corporate GHG reporting, the convention — established under AR5 and continued under AR6 — is to use GWP values without climate-carbon feedbacks for non-CO₂ gases. This maintains methodological consistency with how CO₂ itself is treated in the inventory. The values with feedbacks are published for scientific completeness and are appropriate for some climate-policy analysis contexts, but they are not the values you use in a Scope 1, Scope 2, or Scope 3 inventory.

For long-lived halogenated species (HFCs, PFCs, SF₆, NF₃), the feedback distinction is negligible because their direct warming effect dwarfs any indirect carbon-cycle response. For CH₄ and N₂O, the distinction is material — selecting the wrong column produces an 8–10% systematic bias in the inventory total for those gases.

Complete AR6 dataset — all gases, all time horizons

Source: IPCC AR6 Working Group I, Chapter 7 Supplementary Material, Table 7.SM.7. All values relative to CO₂ = 1. GWP-20, GWP-100, and GWP-500 are time-integrated horizons. The “GC Implementation” column indicates which gases are exposed via the MasterBrain runtime data layer for use in live calculators.

Bold green column (GWP-100, no feedbacks) = the values to use for corporate GHG reporting under the GHG Protocol, ESRS E1, CDP, SBTi, ISO 14064-1, and UNFCCC Paris Agreement reporting. Live = exposed in window.gcMasterBrain at runtime; Reference = published here for completeness, not yet wired into a calculator pathway. SF₆ GWP-500 reflects the IPCC AR6 published value (34,100); see methodology notes.

Every gas, every basis — the full 44-gas matrix

The table above is the curated 12-gas reference set. This is the complete canonical matrix: all 44 gases the corpus carries — including every ANSI/ASHRAE refrigerant blend — across five bases: AR6 at 20, 100 and 500 years, and the AR5 and AR4 100-year values that older reporting regimes still require. Each figure is generated from the same canonical rows the open API serves; an em-dash means the assessment report does not publish that gas (a blank is a fact here, not a gap — HFOs, for instance, postdate AR4).

Filter by gas name 44 gases, alphabetical — click a column header to sort.

Every row is addressable — link to a gas with #gwp-<key>, e.g. #gwp-hfc-410a. Blends are mass-weighted from their constituents per ANSI/ASHRAE Std 34, with the arithmetic recorded in each canonical row’s source reference; the seven blends with an AR4 identity reproduce the EU F-Gas nameplate GWPs exactly. A single value can be pinned to a past edition through the API’s as_of parameter, so a converted figure cited today stays checkable after AR7.

Methane has four GWP-100 values in AR6 — choosing correctly

One of the more confusing aspects of AR6 for practitioners is that methane is associated with four distinct GWP-100 values, used in different contexts — and two of them, 27.0 and 27.9, are close enough that documents citing either look interchangeable when they are not. Choosing the wrong one is one of the most common methodology errors flagged in third-party verification.

Cross-assessment comparison — AR4, AR5, AR6

If your inventory was compiled before 2023, it almost certainly used AR5 GWP values. The shift to AR6 has a quantifiable, gas-specific impact on reported emissions totals. This is not a methodological abstraction — it changes the numbers your assurance provider will check, and in some cases it triggers a base year restatement under the GHG Protocol Corporate Standard.

* AR4 and AR5 did not separately publish fossil and biogenic methane GWP values; both used a single value (25 in AR4, 28 in AR5). AR6 introduced the fossil/biogenic distinction. † 1,430 is the AR4 figure for HFC-134a, not an AR5 one — several HFCs fell from AR4 to AR5 as radiative efficiencies were refined. The AR5 GWP-100 is 1,300, which is the value the GHG Protocol carries in Global Warming Potential Values v2.0 (August 2024) and the one to use; an “AR5” table showing 1,430 is almost certainly an unconverted AR4 table. Per UNFCCC Paris Agreement decisions, parties were required to use AR5 GWP values (without feedbacks) by no later than December 2024.

Field note: when the label is wrong — the EPA supply-chain factors

Which assessment report a dataset uses is usually taken from its documentation. Sometimes the documentation is wrong, and the only way to know is to solve for it. A worked example from our own corpus:

The EPA-lineage US supply-chain emission factors ship as pre-aggregated CO₂e. The PDF bundled with the v1.3.0 release documents AR4 — but it describes v1.2, two data vintages earlier. Trusting it, our own database carried those 1,106 rows labelled AR6 for ten weeks before the discrepancy was caught and corrected. The basis has moved with every release of that series: v1.2 was AR4, v1.3 AR5, and v1.4.0’s published sheet is AR6 with methane at 27.9 — the origin-agnostic value from the table above.

The practical lesson for anyone consuming CO₂e data: a stated GWP basis is a claim, not a property. If the per-gas decomposition is published, verify the claim; if it is not, treat the basis as unverified and say so. Every CO₂e row in the GreenCalculus corpus records its GWP set per row — and where we solved for it rather than read it, the row’s note says that too.

Application — formulas, time horizons, mixing rules

The base conversion formula

Time horizon selection

GWP-100 is the corporate reporting default. Use it for every Scope 1, Scope 2, and Scope 3 inventory unless the reporting framework specifies otherwise.

GWP-20 has two legitimate corporate-reporting use cases. First, where a national policy framework explicitly mandates GWP-20 — New York State’s Climate Leadership and Community Protection Act is the most-cited example, requiring GWP-20 for all GHG accounting under the Act. Second, when communicating short-term mitigation potential of methane-reduction projects (oil and gas leakage abatement, landfill gas capture), GWP-20 better represents the near-term climate benefit and is increasingly seen in voluntary disclosures alongside the GWP-100 figure. GWP-20 is never substituted for GWP-100 in a standard corporate inventory; the two are reported in parallel where both are relevant.

GWP-500 is rare in corporate reporting and primarily appears in long-horizon climate risk modelling.

Live implementation in GreenCalculus calculators

The Scope 1 Stationary Combustion Calculator applies AR6 GWP-100 of 29.8 for fossil CH₄ and 273 for N₂O whenever the calculator is run in Engineering mode. The Regulatory mode reads pre-aggregated DEFRA 2025 CO₂e factors which embed AR5 GWP values (DEFRA’s stated basis, per the DEFRA 2025 Introduction tab, Row 35). The audit trail panel below every result discloses which mode was used and which GWP basis was applied. Both modes are correct disclosures of distinct methodologies — the difference between them is the AR5→AR6 shift in the GWP basis itself.

Framework requirements — which AR version each standard mandates

The transition from AR5 to AR6 is not uniformly mandated across all reporting frameworks. The picture is nuanced: some frameworks have moved to AR6, some preserve AR5 as the legacy default, and some allow either. The table below documents the position as of May 2026, verified against each framework’s current published guidance.

Common reporting errors

Methodology, boundaries, and uncertainty

Primary source and rounding policy

This dataset reproduces the GWP values exactly as published in IPCC AR6 WGI Chapter 7 Supplementary Material, Table 7.SM.7 (Forster et al., 2021). Where IPCC publishes integer values (CO₂ = 1, N₂O = 273), integers are stored. Where IPCC publishes decimal values (CH₄ fossil = 29.8), decimals are preserved. We do not round 29.8 to 30 — the 0.2 unit difference compounds across large inventories with significant methane exposure. Trailing zeroes shown in tables (for example “1,526.0” displayed as “1,526”) are the published values; no rounding has been applied.

Why GWP values vary across published sources

Practitioners encounter methane GWP-100 values ranging from approximately 25 to 32 across different sources. This variation is not noise — it reflects four distinct technical choices:

1. Assessment Report version. AR4 (2007) value was 25; AR5 (2013) was 28; AR6 (2021) is 29.8 for fossil and 27.0 for biogenic.
2. Climate-carbon feedback inclusion. AR6 fossil CH₄ is 29.8 without feedbacks, 32.8 with feedbacks. Earlier assessments did not consistently distinguish.
3. Fossil vs biogenic distinction. Introduced in AR6. Earlier assessments used a single value regardless of origin.
4. Indirect effect inclusion. CH₄ produces ozone and stratospheric water vapour as oxidation products; both are themselves greenhouse gases. AR6 incorporates these indirect effects.

The values on this page are AR6 GWP-100 without climate-carbon cycle feedbacks, fossil and biogenic distinguished, which is the correct combination for corporate GHG reporting under the GHG Protocol family of standards.

Scope applicability — which GWP applies to which inventory line

Uncertainty

IPCC AR6 reports GWP-100 uncertainty ranges of approximately ±20% for CO₂, ±30% for CH₄ and N₂O, and ±10% to ±20% for halogenated species at 90% confidence (per WGI Chapter 7 Supplementary Material). For corporate reporting, point values are used; uncertainty propagates into the inventory total but is not the dominant source of inventory uncertainty in most practical cases. Activity data uncertainty (the mass or volume of the gas emitted) is usually the larger contributor, particularly for fugitive emissions and leak-rate-driven sources.

Geographic applicability

GWP values are global by construction. The Earth’s atmosphere mixes greenhouse gases on timescales much shorter than their residence times, so a tonne of methane emitted in Singapore has the same global warming potential as a tonne emitted in Norway. The geographic adjustment in corporate GHG inventories applies to emission factors (grid intensity, fuel composition, cooking practices) — never to the GWP values themselves.

Implementation and provenance chain

Transparency in factor sourcing is a foundational design principle of GreenCalculus. Every GWP value on this page is directly traceable to a cell in a published IPCC table. This section documents how those values flow from the source document into the calculator outputs.

Data access — REST API and CSV

The IPCC AR6 GWP values on this page are available as a machine-readable REST API endpoint and as a flat CSV download. Both surface the same dataset shown in the table above, sourced from WGI Table 7.SM.7, versioned, and citable.

Citation guidance

If you use this dataset in a published tool, report, or academic work, please cite the IPCC primary source. The GreenCalculus implementation reference is optional but appreciated.

Forster, P., T. Storelvmo, K. Armour, W. Collins, J.-L. Dufresne, D. Frame, D. J. Lunt, T. Mauritsen, M. D. Palmer, M. Watanabe, M. Wild, and H. Zhang, 2021: The Earth’s Energy Budget, Climate Feedbacks and Climate Sensitivity Supplementary Material. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Table 7.SM.7.

IPCC AR6 WGI primary citation

Cite this dataset (GreenCalculus compilation). A versioned, machine-readable snapshot of this table is permanently archived on Zenodo with a citable DOI:

Say, Jeremiah (2026). GreenCalculus — IPCC AR6 Global Warming Potential (GWP) values (machine-readable). GreenCalculus. Zenodo. https://doi.org/10.5281/zenodo.20612456

GreenCalculus dataset DOI (concept — always the latest edition)

Frozen editions: v2026.186 (198 rows, five bases: AR6 20/100/500 + AR5/AR4 100, deposited 7 Sep 2026) · v2025.69 (original 12-gas reference table, deposited 9 Jun 2026).

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