What is the carbon footprint of flying?
About 0.11 to 0.23 kg CO₂e per passenger-kilometre in economy, with radiative forcing (DEFRA 2026): about 1.3 tonnes for a return London–New York flight. Short flights emit more per kilometre, and business class about 2.9 times economy.
A flight’s footprint is the fuel the aircraft burns, shared among everyone on board, plus the extra warming that burning it at altitude causes. Three things decide your share: how far you fly, what kind of flight it is, and how much of the cabin your seat takes up. A single long-haul return in economy can equal two or three months of the world average person’s total emissions, which is why flights are often the largest item in the footprint of people who fly.
Per passenger-kilometre
The most widely used flight factors are the UK government’s (DEFRA) greenhouse gas conversion factors, published every year and used for company reporting. They give kilograms of CO₂e per passenger-kilometre by type of flight and cabin class, in two versions: with and without radiative forcing, the extra warming from contrails and nitrogen oxides at altitude.
| Flight type | With radiative forcing | Without |
|---|---|---|
| UK domestic | 0.22928 | 0.13552 |
| Short-haul, to or from the UK (up to 3,700 km) | 0.12576 | 0.07435 |
| Long-haul, to or from the UK | 0.11704 | 0.06926 |
| International (flights that do not touch the UK) | 0.10916 | 0.06449 |
DEFRA defines the categories by territory, not by distance alone: a flight within the UK is domestic, a flight to or from the UK is short- or long-haul (split at 3,700 km), and a flight between two other countries is “international”. Outside the UK, the international factor is the one to use. The factors cover the fuel burned in flight; producing and delivering the jet fuel adds about a fifth more (DEFRA’s separate well-to-tank factor, 0.02461 kg per passenger-km for long-haul economy).
For comparison, a cruise ship emits about 185 g per passenger-kilometre on Carnival’s fleet in 2025, from the ship’s fuel alone: more than a long-haul economy flight, with or without radiative forcing. See the carbon footprint of a cruise.
Per flight: five routes
Multiply the great-circle distance between the airports by the factor for the flight type. Economy class, with radiative forcing, per passenger:
| Route | Distance | Factor | One way | Return |
|---|---|---|---|---|
| London–Edinburgh (UK domestic) | 534 km | 0.22928 | 122 kg | 245 kg |
| London–Madrid (short-haul) | 1,246 km | 0.12576 | 157 kg | 313 kg |
| New York–Los Angeles (international) | 3,974 km | 0.10916 | 434 kg | 868 kg |
| London–New York (long-haul) | 5,540 km | 0.11704 | 648 kg | 1,297 kg |
| London–Sydney (long-haul) | 17,020 km | 0.11704 | 1,992 kg | 3,984 kg |
London–Sydney is shown as a straight great-circle distance; a real itinerary through a hub such as Singapore or Dubai flies further and emits a little more. For your own trips, the business travel (air) calculator looks up the airports and picks the factor, and the London–New York flights converter turns any CO₂e figure into return transatlantic flights.
Cabin class
A premium seat takes more of the cabin’s floor space, so it is allocated more of the fuel. DEFRA publishes separate factors for each class; on long-haul flights:
kg CO₂e per passenger-km, long-haul to or from the UK, with radiative forcing, and the multiple of economy. Source: DEFRA 2026.
The same London–New York return in business class is about 3,761 kg (11,080 km × 0.3394), against 1,297 kg in economy. For a frequent traveller, the class booked can matter as much as the number of trips.
Radiative forcing: more than the CO₂
Burning jet fuel at cruising altitude does more than release CO₂. Water vapour forms contrails that can spread into cirrus cloud, and nitrogen oxides change ozone and methane. The main scientific assessment, Lee et al. (2021), found that in 2018 aviation’s net effective radiative forcing was 100.9 mW/m², of which contrail cirrus contributed 57.4, CO₂ 34.3 and nitrogen oxides 17.5, and that “non-CO₂ impacts comprise about 2/3 of the net radiative forcing.” The non-CO₂ effects are also the most uncertain, and short-lived: a contrail warms for hours, CO₂ for centuries.
For reporting, DEFRA turns this into a single multiplier on 100-year terms: the “with radiative forcing” factors multiply the flight’s CO₂ by 1.7, which makes them about 1.69 times the factors without it. DEFRA recommends 1.7 as a central estimate while noting that it is “subject to significant uncertainty”. Without radiative forcing, the London–New York economy return is 767 kg instead of 1,297. See the radiative forcing glossary for why 1.7 is lower than the roughly threefold ratio in the physical forcing figures.
Why short flights emit more per kilometre
Take-off and climb burn far more fuel per kilometre than cruising. On a short flight they make up a large share of the trip, so DEFRA’s UK domestic factor, at 0.229 kg per passenger-km with radiative forcing, is almost twice the long-haul economy factor of 0.117. A short flight still emits much less in total than a long one, but it is the least efficient way to cover each kilometre by air, and it is where a train most often wins: see the train vs plane vs car calculator, and the carbon footprint of transport for every other mode.
Which distance to use
Use the great-circle distance between the two airports. Real flights fly further, because of air-traffic routing and holding, but DEFRA has already allowed for that: every DEFRA flight factor includes an 8% uplift on the great-circle distance (2026 methodology, paragraph 8.38), so nothing should be added. Other methods handle it differently. The ICAO Carbon Emissions Calculator adds a fixed correction in kilometres by distance band, and the GLEC Framework adds 95 km to air freight legs. Whichever you use, apply only that method’s own correction; adding another counts the detour twice.
Flying in global emissions
Lee et al. (2021) put aviation’s CO₂ emissions at 1,034 million tonnes in 2018, “approximately 2.4% of anthropogenic emissions of CO₂ (including land use change)”. Counting its non-CO₂ effects as well, aviation was responsible for about 3.5% of the net warming effect of human activity (net effective radiative forcing, 2011, a share the authors expect was about the same in 2018). Aviation’s CO₂ grew by a factor of 6.8 between 1960 and 2018, and about half of all the CO₂ aviation has ever emitted was emitted in the last 20 years of that period.
Against a year’s footprint
A return London–New York economy flight, at about 1.3 tonnes, is roughly a fifth of the world’s average greenhouse gas emissions per person for a whole year (6.6 tonnes in 2024 on the EU’s EDGAR figures) and about 7% of the average American’s 19 tonnes. The personal carbon footprint calculator puts your flights next to the rest of your footprint.
| Two return trips London–Madrid, economy | 2 × 313 kg = 627 kg |
| One return trip London–New York, economy | 1,297 kg |
| Total | ≈ 1.9 t CO₂e |
DEFRA 2026 factors with radiative forcing, great-circle distances. The same three trips with the transatlantic leg in business class come to about 4.4 tonnes (627 + 3,761 kg). Without radiative forcing, the economy total is about 1.1 tonnes.
Frequently asked questions
A return London–New York flight in economy emits about 1.3 tonnes of CO₂e per passenger with radiative forcing (DEFRA 2026: 5,540 km each way at 0.11704 kg per passenger-km), or about 0.77 tonnes without it. In business class the return is about 3.8 tonnes.
It depends on the flight and the car. On DEFRA’s UK factors, a solo petrol car emits less than a UK domestic flight for the same journey but more than most other flights, a second person in the car makes driving lower than economy flying, and an electric car beats flying almost regardless of occupancy. A train on UK national rail is about as low as the electric car. The train vs plane vs car calculator works it out for a journey.
Yes. Because a premium seat takes more of the cabin, DEFRA allocates it more of the fuel. On long-haul flights its factors put premium economy at about 1.6 times economy, business at 2.9 times and first at 4.0 times.
DEFRA recommends it for a fuller picture of aviation’s climate effect, using a multiplier of 1.7 on the CO₂ while noting significant uncertainty. Whichever you choose, say so: the with-RF figure is about 1.69 times the figure without it, so mixing the two makes comparisons meaningless.
In economy, about 0.11 to 0.23 kg CO₂e per passenger-kilometre with radiative forcing on DEFRA’s 2026 factors, highest for short domestic flights. That is about 1.3 tonnes per passenger for a return London–New York flight. Globally, aviation emits about 2.4% of human CO₂ and, counting contrails and nitrogen oxides, causes about 3.5% of the net warming effect.