Flying has more than one carbon rule, and they work in very different ways. This page shows how that happened, what the difference is, and lets you work out what an airline owes under CORSIA.
| EU / UK ETS | CORSIA | |
|---|---|---|
| How it works | There is a limit on total carbon. Airlines buy and sell permits under it. | Airlines pay for carbon above a starting line by buying offset credits. |
| What you pay for | Every tonne of CO2 on the flights it covers | Only the tonnes above 85% of 2019 (the starting line) |
| What you buy | Allowances. There is only one kind, there are only so many, and they are sold on an exchange. | Offset credits from approved groups (Gold Standard, Verra, ACR). Some are better than others, and prices vary. |
| Price | Changes every day. About €80 a tonne (EU) and £72 a tonne (UK) | No one price. Roughly $5 to $20 a tonne, depending on the credit |
| Which flights | Flights inside the area (EU scheme: inside Europe. UK scheme: inside the UK) | Flights between two countries, but only if both countries are in CORSIA |
| Over time | The limit gets smaller every year, to push carbon down | No push to go below the starting line. The aim is just to not grow past 2019 |
| The sum | Tonnes × 1. One allowance for every tonne. Simple. | Tonnes × the growth factor. You pay for a part, not all of it |
SE_y is all the CO2 from every airline, on flights between CORSIA countries, in that year. SE_B,y is the starting line: 85% of the CO2 on those same flights in 2019. ICAO works this out once a year for the whole industry. It is the same number for every airline.
Starting line (85% of 2019): 305,522,071 t CO2. Real CO2 in 2024 on the same flights: 361,159,641 t CO2.
SGF_2024 = (361,159,641 − 305,522,071) / 361,159,641 = 0.15405257. That is the same number ICAO put out. So an airline with 50,000 tonnes on CORSIA flights in 2024 has to offset 50,000 × 0.15405257, which is about 7,703 t CO2.
From 2030, each airline's own growth starts to count too, not just the whole industry's. It counts for 20% from 2030 to 2032, and 70% from 2033 to 2035. This calculator only does the sum from before 2030 for now. I have not built the new part yet.
If an airline uses clean fuel (SAF) that meets CORSIA's rules, it can take that off what it owes. For normal jet fuel, 1 kg burned makes 3.16 kg of CO2. This calculator does not take off the discount yet. So the answer is the most an airline could owe, not the final amount.
| Year | SGF | Status |
|---|---|---|
| 2021 to 2023 (trial) | About 0 (joining was a choice, and COVID reset the starting line) | Out |
| 2024 | 0.15405257 | Out (ICAO, 2025) |
| 2025 and later | Not out yet | ICAO puts out each year's number the year after |