What Changed in 2025: Australia's NGA Factors, UK DEFRA, and US EPA Updates Explained

Every year, the three most widely used emission factor databases — Australia's NGA Factors, the UK's DEFRA Conversion Factors, and the US EPA Emission Factor Hub — publish updated factor sets. And every year, practitioners need to figure out what actually changed and whether it affects their reporting.

The 2025 cycle brought meaningful changes across all three databases. Australia introduced emission factors for an entirely new fuel. DEFRA applied some of the largest reductions in recent years. And the EPA added a new data category that changes how US reporters calculate transmission and distribution losses.

This article walks through each update — what changed, why, and what it means for your next GHG disclosure. If you need background on what these databases are and how they differ, see our complete guide to emission factor databases.

Why annual updates matter

Emission factors aren't static. They change because the real-world systems they represent change. An electricity grid that added 3 GW of solar since last year has a different emission intensity. A fuel supply chain that shifted from one feedstock to another has a different carbon content. Updated economic input-output data changes spend-based Scope 3 factors.

Using outdated factors introduces two problems:

• Accuracy. If your grid's emission intensity dropped 8% but you're still using last year's factor, you're overstating your Scope 2 emissions. That's not conservative — it's inaccurate. And it distorts year-on-year comparisons when you eventually do update.
• Assurance risk. Auditors and assurance providers expect you to use the most recently published factor set at the time of your calculation. Using an older version without documented justification is a common audit finding.

2025 changes at a glance

The overall trend in 2025 is downward. All three databases reflect cleaner electricity grids, improved supply chain data, and methodological refinements that generally reduce emission factors compared to their 2024 predecessors. That's a real signal — grids are genuinely decarbonising — but it also means your reported emissions may fall even if your operations haven't changed. Separating factor-driven changes from operational changes is critical for credible disclosure.

Australia's NGA Factors 2025

New: Scope 1 hydrogen combustion factors

For the first time, the NGA Factors include Scope 1 emission factors for the combustion of hydrogen. This is significant. As Australian industry begins piloting hydrogen in stationary energy, transport, and industrial process applications, reporters now have an official NGER-aligned factor for quantifying associated emissions.

While hydrogen combustion produces no CO2 at the point of use, it does generate nitrogen oxides (NOx) and small quantities of nitrous oxide (N2O) — a potent greenhouse gas. The inclusion of hydrogen combustion factors means organisations using hydrogen as a fuel can now report under NGER using an authoritative Australian factor rather than relying on IPCC defaults or international estimates.

The hydrogen factors are Scope 1 only. Upstream emissions from hydrogen production (grey, blue, or green pathways) remain a Scope 3 consideration and are not covered by these factors.

Updated: Electricity Scope 2 and 3 factors

The NGA state-by-state electricity emission factors — the factors most Australian reporters use for their Scope 2 calculations — have been updated to reflect the latest National Electricity Market (NEM) generation data and Western Australian SWIS data.

The direction is broadly downward across most states, driven by continued growth in renewable generation capacity. South Australia and Tasmania, which already had the lowest grid intensities, saw further reductions. States with higher coal dependence (Queensland, New South Wales) showed more modest declines, though the trend is clearly moving in the right direction.

Scope 3 electricity factors — which capture upstream emissions from fuel extraction, processing, and transport for power generation — were also updated. These tend to move in the same direction as Scope 2 factors but with different magnitudes, since they reflect the fuel supply chain rather than the generation mix directly.

What hasn't changed

Scope 1 emission factors for stationary combustion of conventional fuels (natural gas, diesel, LPG, coal) remain largely unchanged in the 2025 edition. These factors are based on fuel carbon content, which is relatively stable year to year. Transport fuel factors are similarly unchanged. The major movements are concentrated in electricity and the new hydrogen category.

UK DEFRA Conversion Factors 2025

Scope 1 and 2: Reductions exceeding 5%

DEFRA's 2025 Scope 1 factors for major fuel categories — natural gas, gas oil, diesel, petrol — show reductions typically greater than 5% compared to the 2024 edition. For UK electricity (Scope 2), the reduction is even more pronounced, reflecting the continued decarbonisation of the UK grid, which set new records for low-carbon generation share in 2024.

These aren't rounding-error changes. A 5% drop in your natural gas emission factor, applied across a large property portfolio or industrial operation, materially reduces your reported Scope 1 emissions. For organisations tracking toward net zero targets, this is a meaningful tailwind — but it needs to be clearly communicated as a factor-driven change, not an operational improvement.

Scope 3: Reductions exceeding 10%

The largest movements in the 2025 DEFRA set are in Scope 3 categories. Several high-impact categories — including business travel (flights), freight transport, and material use — saw reductions greater than 10%.

This matters enormously for organisations where Scope 3 dominates the inventory (which is most organisations). If you're a professional services firm whose biggest emission source is employee flights, a 10%+ reduction in DEFRA's flight factors will significantly change your headline number — even with identical travel patterns.

• Flights: Updated to reflect improved fleet fuel efficiency and updated load factor data from airline industry reporting
• Hotel stays: Revised using updated grid intensity data for hotel energy consumption across key markets
• Freight: Adjusted for improved vehicle efficiency standards and updated tonne-km data
• Material use and waste: Revised using updated lifecycle data from the UK waste and resources sector

Why such large reductions?

The 2025 DEFRA reductions aren't just about the UK grid getting cleaner (though it is). Several factors converge:

• Updated source data. DEFRA draws on BEIS energy statistics, DUKES (Digest of UK Energy Statistics), and international datasets that were refreshed with 2023-24 data reflecting real decarbonisation progress
• Methodological refinements. Some categories benefited from improved modelling — particularly Scope 3 categories where DEFRA incorporated newer lifecycle data sources
• Global grid improvements. For internationally applicable factors (flights, shipping), the global energy mix is getting cleaner, which feeds through into supply chain factors

US EPA Emission Factor Hub 2025

Updated: eGRID purchased electricity factors

The EPA's eGRID database — which provides subregion-level electricity emission factors across 26 US grid subregions — was updated with 2022 generation data. Most subregions show declining emission intensities, consistent with the continued addition of renewable capacity across the US grid.

The changes vary significantly by subregion. Regions with aggressive renewable buildouts (CAMX in California, NWPP in the Pacific Northwest) saw larger reductions. Coal-heavy regions (RFCW, SRMW) showed more modest changes, though the direction is still generally downward.

For US reporters, this is the most impactful change: eGRID factors drive Scope 2 calculations for any organisation with US electricity consumption. If you operate across multiple subregions, some of your facilities may see larger factor reductions than others.

New: Grid gross loss percentages for T&D losses

This is the most technically significant addition in the 2025 EPA update. For the first time, the EPA now publishes grid gross loss percentages — the percentage of electricity lost during transmission and distribution from power plants to end users.

Under the GHG Protocol, transmission and distribution losses fall under Scope 3 Category 3 (Fuel- and energy-related activities not included in Scope 1 or Scope 2). Previously, US reporters had to estimate T&D loss rates from various indirect sources or use generic national averages. The EPA now provides official, eGRID-aligned loss percentages that can be applied directly.

T&D loss emissions = Scope 2 electricity emissions × grid gross loss percentage. This is a simplified approach — the EPA provides the loss percentages to make this calculation straightforward.

For organisations that previously estimated or ignored T&D losses, this addition provides a clear, auditable methodology. For those already estimating T&D losses, the official EPA percentages may differ from previous estimates, which could change your Scope 3 Category 3 figure.

Updated: Mobile combustion factors

The EPA also updated emission factors for mobile combustion — covering on-road vehicles (passenger cars, light trucks, heavy-duty trucks) and off-road equipment. The changes reflect updated fuel economy data and fleet composition statistics from the Department of Transportation.

The mobile combustion updates are relatively modest compared to the electricity changes, but they're worth noting if your Scope 1 inventory includes a significant vehicle fleet. Factors are provided by vehicle type and fuel type (gasoline, diesel, LPG, CNG).

What this means for your reporting

The 2025 updates share a common theme: emission factors are generally falling, driven by real progress in grid decarbonisation and improved supply chain data. This is good news for the planet, but it creates a reporting communication challenge.

Separate factor changes from operational changes

If your total reported emissions drop 8% this year, your stakeholders (and your board) will want to know why. Was it genuine operational improvement — energy efficiency projects, renewable energy procurement, supply chain optimisation? Or was it largely because the emission factors went down?

Best practice is to restate the prior year using the current year's factors, creating a like-for-like comparison. This lets you clearly show:

• Total change: The headline difference between last year's reported number and this year's
• Factor-driven change: The portion attributable to updated emission factors
• Operational change: The portion attributable to actual changes in your activities

Update your factors promptly

Don't wait. Once the 2025 factors are published, they should be incorporated into your calculation methodology for the corresponding reporting period. If you're an Australian NGER reporter, the August 2025 NGA factors apply to the 2025-26 reporting year. For voluntary corporate disclosures, use the most recently available factor set at the time of your calculation.

Document everything

For every emission factor in your inventory, record:

• Database name and version (e.g., "NGA Factors 2025", "DEFRA 2025 v1.0")
• The specific table, worksheet, and row reference
• The factor value and unit
• Why you selected this source over alternatives

This isn't bureaucracy — it's what separates an auditable inventory from a spreadsheet of numbers. It's also what enables you to quickly identify which of your factors need updating when the next annual release comes.

Frequently asked questions

When exactly are the 2025 factors published?

DEFRA typically publishes in June, NGA in August, and the EPA Emission Factor Hub in April. The exact dates vary each year but generally follow this pattern. Sign up for publisher notifications or check this site — we cover each release as it happens.

Do I need to restate prior year figures when factors change?

There's no universal requirement, but best practice (and the GHG Protocol's guidance on base year recalculation) recommends restating prior years when methodological changes — including factor source changes — materially affect comparability. For internal reporting and trend analysis, restating is essential. For external disclosures, check your framework's specific recalculation policy (CDP, NGER, SECR all have slightly different thresholds).

Can I use 2024 factors for a 2025 reporting year if the 2025 factors aren't published yet?

Yes, if the updated factors haven't been published at the time of your calculation. Document that you used the most recently available version. If the 2025 factors are subsequently published before your disclosure date, best practice is to update — but this is a practical judgement call that depends on your reporting timeline and materiality.

Why do some factors go up while most go down?

Individual factors can increase even in a broadly downward trend. A state grid that added gas capacity while retiring nuclear might see its electricity factor increase. A specific fuel blend might have a higher emission factor due to a change in feedstock sourcing. Always check the factors specific to your activities rather than assuming the overall trend applies to every line item in your inventory.