Same activity, different databases(8 with multiple sources)
2 effective sourcesOnly 2 of 3 sources are truly independent. Some sources cite each other underneath (e.g., GHG Protocol often repackages EPA or DEFRA data). Apparent "multi-source agreement" may be partially circular.
EPA GHG Emission Factors Hub
Edition 2025 · Updated 2025-01-15
0.0414
kg CO2e / passenger-km
🔥Combustion onlyCovers direct combustion emissions (tank-to-wheel). Does not include upstream fuel production, extraction, or transport emissions.
Range: 0.0414 to 0.1038
Original: 0.066 kg CO2 per passenger-mile
Geo: US
DEFRA/DESNZ
Edition 2025 · Updated 2025-06-10
0.1038
kg CO2e / passenger-km
🔥Combustion onlyCovers direct combustion emissions (tank-to-wheel). Does not include upstream fuel production, extraction, or transport emissions.
Range: 0.0414 to 0.1038
Original: 0.10385 kg CO2e per passenger-km
Geo: UK
0.0445
kg CO2e / passenger-km
🔥Combustion onlyCovers direct combustion emissions (tank-to-wheel). Does not include upstream fuel production, extraction, or transport emissions.
Range: 0.0414 to 0.1038
Original: 0.071 kg CO2 per passenger-mile
Geo: US
Uncertainty Range
Cross-source range0.0414
0.1038
Range across 3 independent sources. True uncertainty may be wider.
Key Insight
These 3 sources vary by 98.7%. Geographic fleet composition. US and UK vehicle fleets differ in average vehicle size, fuel efficiency standards, fuel mix, and public transit ridership patterns. US buses tend to show lower per-passenger-km emissions partly due to different occupancy assumptions.
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How to Choose
US and UK factors measure different fleets. Use EPA for US operations, DEFRA for UK. Do not average them.
Source Independence Analysis
How independent are emission factor sources from each other? When GHG Protocol cites DEFRA (UK Department for Environment, Food & Rural Affairs), and DEFRA cites IPCC (Intergovernmental Panel on Climate Change), apparent “multi-source agreement” may be circular citation. Other key sources include EPA (US Environmental Protection Agency) and ICCT (International Council on Clean Transportation). This view maps the actual provenance relationships.
Citation Graph
Primary sourceAggregator (compiles from others)Citation link
EPA = Environmental Protection Agency · DEFRA = Dept for Environment, Food & Rural Affairs · IPCC = Intergovernmental Panel on Climate Change · ICCT = Intl Council on Clean Transportation
Key Finding
GHG Protocol provides no independently derived emission factors in its Cross-Sector Tools. Every factor traces back to EPA, DEFRA, or IPCC. Apparent 'three-source agreement' is circular citation.
0
independent GHG Protocol factors
10
compiled from other sources
Per-Activity Independence (8 multi-source activities)
Passenger Car (Gasoline)
GHG Protocol compiles from EPA. Effective independence: 1 of 2 listed sources.
2 → 1
listed → effective
Air Travel - Long Haul
GHG Protocol compiles from DEFRA. Effective independence: 2 of 3 listed sources.
3 → 2
listed → effective
Bus
GHG Protocol compiles from EPA. Effective independence: 2 of 3 listed sources.
3 → 2
listed → effective
Air Travel - Medium Haul
GHG Protocol compiles from DEFRA. Effective independence: 1.5 of 2 listed sources.
2 → 1.5
listed → effective
Air Travel - Short Haul
GHG Protocol compiles from DEFRA. Effective independence: 1.5 of 2 listed sources.
2 → 1.5
listed → effective
Natural Gas (Stationary Combustion)
GHG Protocol compiles from IPCC. Effective independence: 2.5 of 3 listed sources.
3 → 2.5
listed → effective
Grid Electricity
All 2 sources are independently derived.
2 → 2
listed → effective
Intercity Rail (National Average)
All 2 sources are independently derived.
2 → 2
listed → effective
Activity-based vs. spend-based (USEEIO)(5 activities)
How much does your emission factor change if you use economic spend data instead of physical activity data? USEEIO is EPA's Environmentally-Extended Input-Output model.
Activity-Based Factor
DEFRA/DESNZ
16.1
kg CO2e per room-night
Operational
Spend-Based Factor (USEEIO)
USEEIO v2.0.1-411
NAICS 721 · Accommodation
0.350
kg CO₂e per USD
→ Derived: 52.5 kg CO2e per room-night
Full supply chain (Scope 1+2+3)
Conversion Bridge
0.35 kg/USD × $150/room-night = 52.5 kg CO2e per room-night
Cost assumption: STR Global, average US hotel ADR (average daily rate), 2023
Derived as: 0.35 kg/USD × $150/night = 52.5 kg/night. Hotel rates vary 5x+ from budget motels ($60) to luxury hotels ($300+), making this highly sensitive.
Gap Analysis
3.3x gapLarge gap (5–20x). Spend-based is only suitable for rough screening.Spend-based is higher (226% difference)
•USEEIO includes full supply chain — food service, laundry, amenities, construction amortization — while DEFRA covers operational energy only
•Hotel room rates vary 5x+ by location and tier, making the cost bridge extremely sensitive
•DEFRA factor is UK-specific where grid carbon intensity is ~50% lower than US average, explaining part of the gap
The 3.3x gap is expected — spend-based captures the full hospitality supply chain while activity-based covers only on-site energy. For business travel screening, spend-based is common but imprecise.
When to Use Which
✦ Use spend-based when:
Scope 3 Category 6 (Business Travel) screening when you only have hotel expense totals from corporate travel reports.
✦ Use activity-based when:
When you have room-night counts. Even the simpler DEFRA per-night factor is more stable than spend-based, since it removes price variation.
⚠A $300 luxury hotel night does not produce 2x the emissions of a $150 business hotel. Spend-based factors penalize premium accommodation disproportionately.