How you got here counts too
- By train or bus46 in 100By car or taxithe restHeathrowcounts both
Picture 84 million passengers arriving at Heathrow in a year. Each came by something: the Tube, the Elizabeth line, a coach, a taxi, a lift from a friend. Heathrow counts the carbon of all those journeys as its own, because they only happened to reach the airport. In 2025 that was 398,000 tonnes.
- 201941 in 100 by public transport202343 in 100 by public transport202445 in 100 by public transport202546 in 100 by public transport
The lever is the share of passengers who arrive by public transport. In 2019 it was 41 in 100. In 2025, 46. Heathrow's target was at least 45 by 2026, and it marks that one achieved. The Elizabeth line opened in 2022, between those two readings.
- A taxi to Terminal 3Heathrow's count
Why does Heathrow count a passenger's taxi ride in its own footprint?
Heathrow owns the taxis.
Not yet. It does not. If it did, the ride would be scope 1. The ride is counted because it was caused, which is the third ring.It does not; the passenger counts it.
Not yet. The passenger may count it too. Scope 3 is shared: the same tonne sits in the airport's count and the traveller's, as lesson 3 showed.The ride only happened to reach the airport, so the airport caused it without owning it: scope 3.
Right. This is scope 3 from lesson 3. Nobody at Heathrow drove the taxi. The airport is why the journey exists, and the rules say count what you cause. Move the control through the years. Each frame is Heathrow's own figure: the share arriving by public transport, and the carbon from passengers' journeys.
41 in 100By public transport632,000 tonnesJourney carbonYear: 2019
2019: 41 in 100 by public transport, and 632,000 tonnes from passengers' journeys.
43 in 100By public transport436,000 tonnesJourney carbonYear: 2023
2023: 43 in 100; 436,000 tonnes. Fewer passengers than 2019 also pulled this down, Heathrow says.
45 in 100By public transport429,000 tonnesJourney carbonYear: 2024
2024: 45 in 100; 429,000 tonnes.
46 in 100By public transport398,000 tonnesJourney carbonYear: 2025
2025: 46 in 100; 398,000 tonnes. Heathrow itself warns that this figure will likely be revised upward as it improves how it counts.
The share rose 5 points and the carbon fell by about a third. Can the share alone explain that?
No. The carbon figure must be wrong.
Not yet. It is Heathrow's count and may yet be revised, as its own report says. Wrong is not the claim; incomplete explanation is.Yes. More trains, less carbon, that is the whole story.
Not yet. The share moved 41 to 46. If that were the whole story the carbon would fall by about a twelfth, not a third. Something else moved too.No. Heathrow says fewer passengers up to 2023 and the way it counts explain part of it, and warns the method is being refined.
Right. Five points of share cannot cut a third of the carbon on its own. Heathrow credits lower passenger numbers up to 2023 for part of the fall, and says the surface access figures are likely to be revised as it refines how it counts.Move the control.
- 46 in 100Heathrow's survey41 in 100Government's figures, 2023
Two surveys, two numbers. Heathrow's own passenger survey says 46 in 100 arrive by public transport. The government's figures for 2023 said 41. They ask different people in different ways. The target was written against Heathrow's survey, so Heathrow's survey says it is met. Which number is right is a fair question with no settled answer.
A draft government rule for an expanded Heathrow would require at least what share by public transport once the airport passes 130 million passengers?
Pick one. Nothing is scored.
Today, Heathrow's survey46 in 100Rule at 116 million50 in 100Rule at 130 million55 in 10055 in 100.Fifty-five in 100, and 50 at 116 million passengers. Against today's 46 on Heathrow's own survey, or 41 on the government's. Guesses tend to land on 50, the round number.- 84,000 staffJourneys to and from work116,000 tonnes in 2019136,000 tonnes in 2025
Staff journeys count too: about 136,000 tonnes in 2025, up from 116,000 in 2019. More than 84,000 people work across the airport, and Heathrow does not say why their journeys' carbon rose. Its target is that no more than 57 in 100 of staff trips are a lone driver in a car. In 2024 it was 52.
- 60,000 fansjourneysStadium's count500 tonnes?
A new stadium will hold 60,000 people. Its owners publish a footprint of 500 tonnes a year: floodlights and heating. A council officer says the fans' journeys are missing. Using Heathrow's rule, who is right?
The owners. A stadium does not drive the fans there.
Not yet. Neither does Heathrow drive its passengers. Causing a journey is the test, not driving it, and the stadium is why 60,000 journeys happen.The officer. The fans' journeys only happen to reach the stadium, so they are its scope 3, like Heathrow's taxis.
Right. Sixty thousand journeys a match, caused by the stadium and owned by nobody at it. That is exactly the ring Heathrow counts for passengers and staff.Neither. Journeys cannot be counted.
Not yet. Heathrow counts them every year from surveys of how people arrived. It is a survey estimate rather than a meter reading, and it is a count.
Lesson complete
The trip to the airport is in the airport's count, and the share arriving by train is the lever.