How aviation ended up with more than one carbon scheme, how EU/UK ETS and CORSIA actually differ mechanically, and a working calculator for CORSIA's offsetting requirement.
| EU / UK ETS | CORSIA | |
|---|---|---|
| Mechanism | Cap-and-trade | Offsetting against a baseline |
| What's priced | Every tonne of CO2 on covered flights | Only tonnes above 85% of 2019 levels (the baseline) |
| What you buy | Allowances (EUA/UKA) - one instrument, capped supply, exchange-traded | Eligible emissions units from approved offset programs (Gold Standard, Verra, ACR) - heterogeneous quality and pricing |
| Price behaviour | Market-driven, moves daily; ~€80/t (EU), ~£72/t (UK) | No single traded price; unit prices vary by program, roughly $5-20/t |
| Route scope | Intra-jurisdiction (EU ETS: intra-EEA; UK ETS: domestic UK) | International flights between two CORSIA-participating states only |
| Trajectory | Cap tightens yearly (Linear Reduction Factor) - deliberately drives emissions down | No mandated reduction below baseline, just "no net growth" above 2019 |
| Compliance math | Emissions × 1 allowance/tonne - full exposure, no formula | Emissions × Sector's Growth Factor - a fraction, not the whole |
SE_y is total sectoral CO2 emissions, across all operators, for CORSIA-applicable State pairs in year y. SE_B,y is the baseline: 85% of total 2019 sectoral CO2 emissions for those same State pairs. ICAO calculates and publishes this centrally, once a year, for the whole sector, not per operator.
2019 baseline (85% of applicable 2019 emissions): 305,522,071 t CO2. Actual 2024 emissions for the same State pairs: 361,159,641 t CO2.
SGF_2024 = (361,159,641 − 305,522,071) / 361,159,641 = 0.15405257, exactly what ICAO published. An operator with 50,000 t of CORSIA-covered emissions in 2024 owes 50,000 × 0.15405257 ≈ 7,703 t CO2 of offsetting.
From 2030, an Individual Growth Factor (an operator's own emissions growth, not just the sector's) enters the calculation alongside SGF, rising from 20% weight (2030-2032) to 70% weight (2033-2035). This calculator currently applies the pre-2030, 100%-sectoral formula only, the individual growth factor blend is not yet implemented, flagged above as unreviewed.
An operator's final offsetting requirement for a compliance period is reduced by any emissions reductions claimed from CORSIA-eligible fuels (SAF that meets CORSIA's own eligibility criteria, using a fuel conversion factor of 3.16 kg CO2/kg for Jet-A). That deduction isn't in this calculator yet, current output is the pre-deduction offsetting requirement, a ceiling, not the final number an operator would actually owe after claiming eligible fuel use.
| Year | SGF | Status |
|---|---|---|
| 2021-2023 (Pilot) | ~0 (voluntary, baseline effectively reset post-COVID) | Published |
| 2024 | 0.15405257 | Published (ICAO, 2025) |
| 2025 onward | Not yet published | ICAO publishes each year's SGF the following year |