Carbon Accounting for Aviation and Airlines

Aviation Emissions Overview - Understanding the Full Climate Impact

Aviation remains one of the fastest-growing sources of greenhouse gas emissions globally. Commercial aviation accounts for approximately 2.5% of global CO2 emissions, but the picture becomes more complex when considering radiative forcing - the actual warming effect. When accounting for contrails, nitrogen oxides, and other non-CO2 effects, aviation's contribution rises to around 3.5% of effective radiative forcing, making it a significant player in climate change despite its relatively modest share of energy-related emissions.

The growth trajectory is concerning. As global travel demand continues to increase, aviation emissions are projected to rise significantly through 2026 and beyond. This expansion has prompted regulators worldwide to implement stricter monitoring and reporting requirements, making accurate carbon accounting essential for airlines operating across multiple jurisdictions.

For airlines and aviation stakeholders, understanding the total climate impact - not just direct CO2 - is crucial for meeting regulatory expectations and setting credible net-zero commitments. Most regulatory frameworks now emphasize comprehensive measurement methodologies that capture the full scope of aviation's environmental footprint.

Key Emission Sources in Aviation - Breaking Down Scope 1, 2, and 3

Scope 1: Direct Jet Fuel Combustion

Scope 1 emissions represent the largest component of airline carbon accounting. Jet fuel combustion from aircraft operations generates CO2 emissions at predictable rates: approximately 3.15 kg of CO2 per kilogram of jet fuel burned. Airlines track Scope 1 emissions using fuel consumption data from flight operations, usually measured in kilograms or metric tons of fuel per flight, route, or reporting period.

Accurate Scope 1 calculation requires reliable fuel records from:

• Fuel uplift data at each airport
• Flight consumption logs
• Aircraft fuel efficiency metrics
• Fuel type specifications (Jet A-1, Jet A, alternatives)

This is typically the most straightforward emission source to measure, though global fuel accounting can involve complexities around fuel tanking practices and international flight attribution.

Scope 2: Ground Operations and Purchased Electricity

Scope 2 emissions arise from electricity consumed at airport terminals, maintenance facilities, offices, and ground support operations. These emissions depend on the grid carbon intensity in each country where the airline operates.

Common Scope 2 activities in aviation include:

• Terminal building heating, cooling, and lighting
• Baggage handling systems
• Aircraft servicing equipment
• Administrative offices
• Hangar operations

Airlines must obtain grid emission factors from electricity suppliers or use national average factors published by environmental agencies. EU ETS Explained provides detailed guidance on how European utilities report these factors - a useful reference even for non-European operators seeking best-practice methodologies.

Scope 3: Purchased Goods, Services, and Value Chain Emissions

Scope 3 emissions represent the most complex category for airlines. They include catering supply chains, ground transportation services, hotel accommodations for crew, maintenance outsourcing, and procurement of aircraft and parts. Some frameworks also require airlines to account for "radiative forcing index" (RFI) multipliers that estimate non-CO2 warming effects from cruise altitude emissions.

Airlines increasingly struggle to obtain reliable emissions data from suppliers, making Scope 3 calculation methodology a key differentiator between comprehensive and basic carbon accounting systems.

CORSIA - ICAO's Mandatory Carbon Offsetting Scheme

The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) represents the first global carbon measure applicable to the aviation sector. Established by the International Civil Aviation Organization (ICAO) in 2016, CORSIA is becoming mandatory for all airlines operating international flights from 2027 onwards.

CORSIA Compliance Requirements from 2027

Starting in 2027, airlines must:

• Monitor CO2 emissions from all international flights
• Calculate emissions annually using ICAO-approved methodologies
• Offset emissions above 2020 baseline levels through verified carbon credits
• Report compliance data to their national aviation authorities

The 2020 baseline is critical: airlines only offset growth in emissions relative to this reference year. This creates an incentive for early action - airlines with higher 2020 baselines face greater offsetting obligations if future emissions increase.

Which Airlines Must Comply with CORSIA

CORSIA applies to all airlines operating international flights that:

• Carry over 10,000 passengers annually (around 90% of international traffic)
• Are registered in ICAO member states
• Operate aircraft with maximum takeoff weight exceeding 5,700 kg

Exemptions exist for least developed countries and small island developing states, providing some flexibility for developing aviation markets.

EU ETS Aviation - European Regulatory Framework

The EU Emissions Trading System (ETS) has covered aviation since 2012, making it significantly older than CORSIA. All flights departing from or landing in EU member states must participate, regardless of airline nationality. This creates a second, parallel compliance obligation for most international carriers.

Under EU ETS aviation rules, airlines receive allowances for free allocation (declining over time) and must purchase allowances for emissions exceeding these allocations. The carbon price is significantly higher than typical voluntary offset prices, creating strong economic incentives for emission reductions.

Airlines operating within Europe must understand how EU ETS aviation interacts with CORSIA to avoid double-counting or inefficient compliance strategies.

UK ETS Aviation - Post-Brexit Extension

Following Britain's departure from the EU, the UK established its own emissions trading system that includes aviation. UK ETS Explained covers this framework comprehensively, but the key distinction is that UK ETS aviation covers UK domestic and intra-UK flights (not EU/international routes), creating a focused but distinct regulatory requirement for airlines operating from UK airports.

Airlines must track emissions separately for:

• Flights entirely within UK airspace (UK ETS scope)
• EU flights (EU ETS scope)
• International flights (CORSIA scope)

This creates reporting complexity, especially for routes starting or ending at UK airports.

Sustainable Aviation Fuels (SAF) and Carbon Accounting

Sustainable Aviation Fuels offer the most direct pathway for airlines to reduce their carbon footprint within current operational frameworks. SAF is produced from feedstocks including used cooking oil, waste biomass, algae, and power-to-liquid synthetic fuels.

How SAF Credits Impact Carbon Accounting

SAF carbon accounting uses "lifecycle assessment" (LCA) methodology, which measures emissions across the entire fuel production chain, from feedstock cultivation through refining and distribution. A typical sustainable aviation fuel might reduce lifecycle emissions by 50-80% compared to conventional jet fuel, depending on feedstock and production method.

When an airline blends SAF with conventional jet fuel, emission reductions are calculated proportionally. A 50% SAF blend delivers approximately 25-40% emission reduction per flight (depending on SAF type), though regulatory frameworks may attribute these benefits differently.

Under CORSIA, SAF-related emission reductions can lower an airline's baseline obligations. Under EU ETS, airlines can claim actual emission reductions from SAF use, reducing allowance requirements. This dual benefit makes SAF particularly attractive economically.

FAQ

How do airlines calculate their carbon emissions?

Airlines use standardized methodologies from ICAO, which measure fuel consumption multiplied by carbon emission factors (typically 3.15 kg CO2 per kg of jet fuel). Airlines gather fuel data from flight operations systems, multiply by appropriate emission factors, and aggregate across their fleet. Scope 2 and Scope 3 emissions require additional data collection from suppliers and facilities. Many airlines now use specialized platforms like Greenio to automate this calculation and ensure consistency across multiple data sources.

What is CORSIA and who must comply?

CORSIA is ICAO's Carbon Offsetting and Reduction Scheme for International Aviation, becoming mandatory from 2027. All airlines operating international flights carrying over 10,000 annual passengers must participate. Airlines monitor emissions annually, calculate growth relative to 2020 baselines, and purchase verified carbon offsets for emissions above baseline levels.

How do Sustainable Aviation Fuels reduce an airline's carbon footprint?

SAFs reduce lifecycle emissions by 50-80% compared to conventional jet fuel, depending on feedstock and production method. When used in blended mixtures, SAF proportionally reduces total flight emissions. Airlines can claim these reductions against CORSIA obligations and EU ETS allowance requirements, creating dual regulatory benefits that improve financial returns on SAF investments.

Does the EU ETS apply to all European flights?

EU ETS aviation applies to all flights departing from or landing in EU member states, regardless of airline nationality or destination. However, some exemptions exist for flights from remote regions and aircraft below certain weight thresholds. The framework has covered aviation since 2012, predating CORSIA by 15 years.

Why is understanding radiative forcing important for aviation emissions reporting?

Radiative forcing captures non-CO2 warming effects from contrails, NOx, and cirrus cloud formation at cruise altitude. Aviation's effective climate impact is 1.4-2 times higher than CO2 emissions alone. Regulators increasingly expect airlines to acknowledge these multiplier effects when setting climate targets, even if accounting frameworks use CO2-only metrics for compliance purposes.

Conclusion

Carbon accounting for aviation has evolved dramatically as regulatory frameworks multiply and climate expectations intensify. Airlines now navigate CORSIA mandates from 2027, existing EU ETS frameworks, UK-specific regulations, and investor demands for comprehensive emissions disclosure spanning Scope 1, 2, and 3 categories.

The pathway forward combines accurate measurement, sustainable fuel adoption, and operational efficiency improvements. Airlines that implement robust carbon accounting today - measuring not just compliance minimums but total climate impact - are best positioned to meet 2026 stakeholder expectations and prepare for tightening regulations through the rest of the decade.