What radiative forcing means
A plane's engines produce CO2, like any engine. But at cruising altitude they also produce contrails, water vapour and nitrogen oxides, which trap extra heat. Scientists call this extra warming effect radiative forcing. It is real, but harder to measure than CO2, so the government handles it with a multiplier.
The Department for Energy Security and Net Zero recommends a multiplier of 1.7 as a central estimate, applied only to the CO2 part of flight emissions. It says the figure is uncertain, and that there is no better way to account for these effects at present. It publishes every flight factor twice, with and without the uplift, so you can choose.
How much difference it makes
Government factors for 2026, average passenger, kg CO2e per passenger km, excluding well-to-tank:
| Flight | Without radiative forcing | With radiative forcing | Difference |
|---|---|---|---|
| Domestic (within the UK) | 0.13552 | 0.22928 | +69% |
| Short-haul (UK to Europe) | 0.075590 | 0.12786 | +69% |
| Long-haul | 0.090430 | 0.15282 | +69% |
The difference is less than 70% because the multiplier only applies to the CO2, not to the small amounts of methane and nitrous oxide in the factor, and because of rounding in the published tables.
A worked example
One person flies from Heathrow to Edinburgh and back. The straight-line distance is about 535 km each way, so 1,070 passenger km in total:
- Without radiative forcing: 1,070 × 0.13552 = 145 kg CO2e
- With radiative forcing: 1,070 × 0.22928 = 245 kg CO2e
For comparison, the 2026 factor for national rail is 0.030920 kg CO2e per passenger km, so the train is a fraction of either flight figure, even allowing for the longer route by rail. Moving domestic flights onto trains is one of the easiest reductions to put in a Carbon Reduction Plan.
Three mistakes to avoid
- Adding 8% to the distance. The government's flight factors already include an 8% uplift for indirect routes, delays and circling. Use the straight-line distance between the airports, and don't add anything to it.
- Applying 1.7 yourself. If you use the "with radiative forcing" factor, the uplift is already in it. Multiplying again counts it twice.
- Switching basis between years. Moving from "without" to "with" will look like your travel emissions jumped by up to 70%. Pick one, use it every year, and if you change, restate your baseline and explain why.
Cabin class matters more than most people think
Long-haul factors for 2026, with radiative forcing, kg CO2e per passenger km:
| Cabin | Factor | Compared with economy |
|---|---|---|
| Economy | 0.11704 | 1.0× |
| Premium economy | 0.18726 | 1.6× |
| Business | 0.33940 | 2.9× |
| First | 0.46814 | 4.0× |
If your booking data shows the cabin, use it. If it doesn't, the "average passenger" factor is the fallback. Domestic flights only have an average factor, whatever the seat.
What to write in your report
The GHG Protocol leaves the radiative forcing correction optional but asks you to disclose the factor you used. A line like this covers it: "Flights are calculated from great-circle distances using the UK government conversion factors for 2026, including the radiative forcing uplift."
Flights are Scope 3 category 6, business travel, which a PPN 006 Carbon Reduction Plan must include. Hotel nights on the same trips go in the same category; see our post on counting hotel stays.
How Carbon Recycling helps
Enter a flight by airport codes and Carbon Recycling works out the distance, the flight type and the emissions with the right year's government factor, including radiative forcing by default. Your report states the basis, and you can switch it off in settings if a customer asks for figures without it.