AR5 vs AR6 Global Warming Potentials: The...

A refrigerant service docket lands in the sustainability inbox. Ten kilograms of R-410a topped up on a chiller at a distribution centre. That single line has to be recorded twice if the reporter is inside both the NGER regime and AASB S2. Not because anyone wants to double the work. Because the two regimes disagree on how much warming that R-410a actually causes.

NGER uses AR5 GWP values. AASB S2, tracking the ISSB baseline, expects AR6. Ten kilograms of R-410a under AR5 becomes 19.24 tonnes of CO2-e. The same ten kilograms under AR6 becomes 22.56 tonnes. Small on a single docket. Meaningful on a national portfolio of 200 sites and 40 refrigerant events per quarter.

This is not a rounding issue. It is a policy divergence baked into two active regulatory frameworks, and finance teams reporting under both need a workable way to reconcile them without maintaining two parallel emission ledgers.

Why Australia is running two GWP sets at once

The NGER Measurement Determination sets the emission factors used for NGER submissions, and regulation 2.02 of the NGER Regulations sets the GWPs. The GWP values are pinned to the IPCC Fifth Assessment Report (AR5), published in 2013. Safeguard Mechanism baselines and NGER-covered facility data all sit inside that AR5 envelope.

AASB S2, issued by the AASB in September 2024, points reporters at the ISSB IFRS S2 baseline. IFRS S2 references the most current IPCC assessment. That is now AR6, published in 2021. So an AASB S2 reporter disclosing Scope 1 fugitive emissions in a general purpose financial report is expected to use AR6 GWPs, even if the same underlying activity data feeds an NGER submission using AR5.

The AASB has provided some jurisdictional relief. AASB S2025-1, approved on 15 December 2025, allows NGER reporters to use AR5 GWPs in their AASB S2 disclosure for the NGER-covered portion of their emissions. According to the AASB, it applies to annual periods beginning on or after 1 January 2027, with earlier application permitted, so check with your auditor whether you are electing early application. The relief is narrow. It does not extend to the parts of a corporate footprint that fall outside NGER coverage, and it does not apply to entities that report under AASB S2 without being NGER reporters.

Read plainly, the practical outcome is this. An NGER reporter with a portfolio that maps cleanly to their NGER boundary can hold AR5 for both. Everyone else needs to run both GWP sets. See our companion post on AR5 vs AR6 methane reporting for NGER and AASB S2 for the underlying methane story.

The full comparison table

Below are the values that matter most for Australian reporters. AR5 100-year GWPs (no climate feedback, as adopted in regulation 2.02 of the NGER Regulations) alongside AR6 100-year GWPs as published by IPCC WG I. NGER applies one methane value, 28, to fossil and biogenic methane alike, so the AR5 figure of 30 sometimes quoted for fossil methane does not apply to NGER reports.

Gas	AR5 GWP (100-yr)	AR6 GWP (100-yr)	Change	Where it hits
CH4 (fossil)	28	29.8	+6.4%	Coal seam gas, natural gas leaks, ventilation air methane
CH4 (biogenic)	28	27	-3.6%	Landfill, wastewater, agriculture, biomass combustion
N2O	265	273	+3.0%	Diesel and petrol combustion, nitrogen fertiliser, wastewater
HFC-32 (R-32)	677	771	+13.9%	Split system aircon, VRV/VRF systems
HFC-134a (R-134a)	1,300	1,530	+17.7%	Automotive AC, refrigeration, some chillers
R-410a blend	1,924	2,256	+17.3%	Commercial chillers, larger split systems
R-404a blend	3,943	4,728	+19.9%	Supermarket refrigeration, cold storage, food logistics
SF6	23,500	24,300	+3.4%	Electrical switchgear

Two things stand out. Methane barely moves in absolute terms but the fossil vs biogenic distinction has become sharper and matters for landfill and wastewater reporters. High-GWP refrigerants shift materially, and the R-404a change in particular puts pressure on food, cold storage, and supermarket portfolios where R-404a is still in service.

Scope 1 fugitive emissions is where the money is

Fugitive emissions is the category most affected by the AR5 to AR6 shift. Refrigerant leakage from commercial HVAC, coal seam gas venting from resource operations, ventilation air methane from underground coal mines, and landfill CH4 all sit in Scope 1 and all move under AR6.

Take a distribution centre operator with 40 refrigerant service events a year across 12 sites. Roughly 400 kg of R-410a topped up annually (a common leakage profile at around 15% of installed charge). Under AR5 that is 770 tonnes CO2-e. Under AR6 it is 902 tonnes. A 133-tonne swing on a single line item, with no change to the underlying activity data.

Now shift the same operator to R-404a legacy equipment. Same 400 kg annual leakage. AR5 gives 1,577 tonnes. AR6 gives 1,891 tonnes. A 314-tonne shift in the AASB S2 figure. It does not touch a Safeguard baseline comparison, which stays in AR5. The refrigerant story is covered in more depth in our refrigerant emissions Scope 1 tracking post.

Coal seam gas and ventilation air methane operators face a more constrained problem. The methane GWP itself barely moves, but the biogenic vs fossil split matters for reporters with mixed sources. Under AR6 the fossil and biogenic origin changes the GWP applied, while NGER applies 28 to both, so expect assurance providers to ask how that split was made.

Scope 1 combustion CH4 and N2O

The impact on combustion emissions is smaller but not zero. Diesel combustion produces trace CH4 and N2O alongside the dominant CO2. The CH4 movement is negligible. The N2O movement is 3% higher under AR6.

For a construction fleet burning 800,000 litres of diesel a year, CO2 dominates at around 2,160 tonnes CO2-e. The CH4 and N2O contribution is a small fraction of that, and moving it from AR5 to AR6 changes the total by less than a tonne. Not material at that scale.

Where it does matter is nitrogen fertiliser application in agriculture, where N2O is the dominant emission rather than a trace contribution. A grain grower applying urea across 5,000 hectares can see the N2O portion move 3% under AR6, and on a footprint dominated by N2O that flows through directly.

Scope 3 Category 3 fuel and energy related activities

Upstream fuel supply chains carry a methane exposure through natural gas extraction and pipeline leakage. If a reporter uses well-to-tank (WTT) factors on natural gas, or other factors that include upstream methane leakage, the AR5 to AR6 shift on fossil CH4 comes through in Category 3.

The absolute movement is modest (fossil CH4 rises from NGER's single value of 28 to 29.8 under AR6). The direction is worth noting.

For most reporters this line item is dwarfed by Scope 3 Category 1 purchased goods and services. But food, logistics, and industrial reporters with significant upstream gas exposure need to record which factor version they used and disclose it.

Safeguard Mechanism baselines under the two regimes

Safeguard baselines sit inside NGER and are calculated under AR5. A Safeguard reporter comparing this year's covered emissions against baseline is doing that arithmetic entirely in AR5 space, and will continue to do so.

Where the friction shows up is in the same Safeguard reporter's AASB S2 climate disclosure. The financial report picks up AR6 for the same facility, unless the AASB S2025-1 relief covers it. Without the relief, facilities dominated by high-GWP refrigerants or fossil methane show a larger Scope 1 number than the NGER submission, and those dominated by biogenic methane show a smaller one. Two numbers, both correct under their respective regimes, and both needing to appear in the same annual report cycle.

Expect assurance providers to ask for that reconciliation. See our methane management plans for Safeguard Mechanism post for the sector-specific detail on the underground coal and gas side.

The reconciliation approach: one activity ledger, two GWP layers

A common mistake in the industry is teams building two separate spreadsheets. One for NGER using AR5, one for AASB S2 using AR6. Same activity data entered twice. Different totals. Different rounding. Different lock dates. Different assurance evidence. By month three of the reporting cycle nobody can remember which sheet is the source of truth.

The correct architecture is to store activity data once, at the source-document level, and apply the GWP set at report render time. A 10 kg R-410a top-up is stored as one record with the gas identity, mass, service date, site, and the source docket. The record does not carry a CO2-e value at all. The CO2-e is computed by the report generator using whichever GWP set the report demands.

Carbonly differs from that pattern in one way worth stating plainly. Every emission record keeps the activity data (litres, kilograms, kilowatt-hours) with the source document attached, but the ledger also calculates and stores a CO2-e value, and it does so under AR5 only, the set regulation 2.02 of the NGER Regulations applies. Expressing those same quantities under AR6, for the portion of an inventory that sits outside the AASB S2025-1 relief, has to be done as a separate reporting step, and you should treat it that way when you evaluate us. The part that is already true is the part that matters most: the activity data never moves, so the AR6 view is a reporting question rather than a data migration.

An activity-first record also helps if NGER moves to a later assessment report. When the Regulations change (whenever that lands), the historical activity data is untouched, past NGER submissions stay on the AR5 basis they were made under, and new figures can be calculated from the stored quantities rather than by re-keying source documents.

Worked examples

Example 1: Refrigerant service docket. A shopping centre operator services a chiller and tops up 15 kg of R-410a on 3 April 2026.

Activity record: 15 kg R-410a, chiller SN-2341, site "Site A", docket "SVC-88213".
NGER report (AR5): 15 x 1,924 = 28,860 kg CO2-e = 28.86 t CO2-e
AASB S2 report (AR6): 15 x 2,256 = 33,840 kg CO2-e = 33.84 t CO2-e
Delta: 4.98 t CO2-e (17.3%)

Example 2: Underground coal mine ventilation air methane. A mine reports 12,000 t CH4 vented through the ventilation shaft over the year (fossil origin).

Activity record: 12,000 t CH4 fossil, VAM source.
NGER report (AR5): 12,000 x 28 = 336,000 t CO2-e
AASB S2 report (AR6): 12,000 x 29.8 = 357,600 t CO2-e
Delta: +21,600 t CO2-e (+6.4%)

Note the direction. Fossil methane goes up under AR6, because NGER applies 28 to all methane while AR6 gives fossil methane 29.8. On the same activity data, the AASB S2 figure lands above the NGER figure.

Example 3: Landfill CH4 (biogenic). A council operates a legacy landfill and reports 8,500 t CH4 emissions after capture, all biogenic origin.

Activity record: 8,500 t CH4 biogenic, first order decay model output.
NGER report (AR5, using the single regulation 2.02 CH4 GWP of 28): 8,500 x 28 = 238,000 t CO2-e
AASB S2 report (AR6): 8,500 x 27 = 229,500 t CO2-e
Delta: -8,500 t CO2-e (-3.6%)

Biogenic methane goes down under AR6. Landfill and wastewater operators will see their AASB S2 numbers land slightly below their NGER numbers, all else equal.

The takeaway across the three examples is that direction is not uniform. Refrigerants go up. Fossil methane goes up. Biogenic methane goes down. N2O goes up. The narrative in the sustainability report needs to explain the movement rather than treat AR5 to AR6 as a single directional shift. The AASB S2 lines show the AR6 figure; where the AASB S2025-1 relief applies to the NGER-covered portion, the AR5 figure can be carried in both.

What you get from Carbonly for the two GWP sets

The verified capabilities in the platform that address this problem:

Activity data on every record. Every emission record keeps the activity data (mass, volume, energy) and the source document behind it.
AR5 is the set the ledger commits. Calculations are written against AR5, which is what regulation 2.02 requires for NGER and what AASB S2025-1 permits for the NGER-covered portion of an AASB S2 disclosure. The platform does not produce an AR6 version of the same records. If that matters to your FY27 plan, plan for it as a separate step rather than assuming it is live.
Factor version on every record. Each emission record carries the emission factor version it was calculated with, so a reported figure can be traced back to the factor behind it.
Evidence pack for assurance. The evidence pack export gives an auditor the trail from a reported figure back to its source documents.

What Carbonly does not do: we do not have a PCAF financed emissions module, a GRESB submission generator, or a CBAM export, and the ledger writes AR5 only. The ledger is an AR5 emission ledger, and an AR6 view is not a separate module or a second stored calculation. See our NGA vs GHG Protocol reconciliation post for the parallel factor-set problem on the electricity side.

Pricing is a per-project licence with an A$100 per month workspace minimum and no per-seat fees. Reporters running 40+ refrigerant events per quarter across a national portfolio can walk the workflow with us at hello@carbonly.ai before deciding.

FAQ

Does NGER use AR5 or AR6? AR5. Regulation 2.02 of the NGER Regulations is pinned to AR5 GWPs. Safeguard baselines and NGER submissions all sit inside the AR5 envelope. A future amendment to the Regulations may shift this; it has not landed as of the 2025-26 reporting year.

Does AASB S2 use AR5 or AR6? AR6. AASB S2 aligns with ISSB IFRS S2, which references the current IPCC assessment. AR6 is the current assessment. AASB S2025-1 provides jurisdictional relief allowing NGER reporters to use AR5 for the NGER-covered portion of their AASB S2 disclosure, but the default expectation is AR6.

Do I need to submit twice? Not the same numbers, but yes to two reports. NGER goes to the Clean Energy Regulator by 31 October under AR5 (for 2025-26, by midnight AEDT on Monday 2 November 2026, because 31 October falls on a Saturday; the CER has said there are no extensions). The NGER October 2026 deadline preparation guide covers the final checks. AASB S2 sits inside the general purpose financial report under AR6 (or AR5 if the AASB S2025-1 relief applies to your NGER-covered portion). The activity data underneath is the same. Only the GWP layer differs.

Which GWP applies to my Safeguard Mechanism baseline? AR5. Safeguard is calculated under NGER, which is AR5. Any comparison of covered emissions against baseline is done entirely in AR5 space. If your AASB S2 disclosure reports that facility under AR6 (outside the AASB S2025-1 relief), it produces a different absolute number, and you should expect to explain the difference in the disclosure.

How much does the GWP shift move the total number? It depends on your gas mix. A portfolio dominated by CO2 combustion sees almost no movement (well under 1%). A portfolio with heavy R-404a refrigerant exposure can move 15-20% on that line item alone. A portfolio dominated by biogenic methane (landfill, wastewater) will see the total drop 3-4% under AR6. There is no single number; the answer sits inside the gas breakdown.

AR5 vs AR6 Global Warming Potentials: The Calculation Impact for Australian NGER and AASB S2 Reporters