Picture three kinds of smoke at Heathrow. A boiler heating Terminal 5: the airport owns it. The power station that makes the electricity for the lights: the airport buys the power, but someone else burns the fuel. A British Airways jet taking off: the airport owns neither the plane nor the fuel.
Scope 1: your own fires→Scope 2: your electricity→Scope 3: caused, not owned
The world's counting rules sort carbon into three scopes. The word scope just means which ring of smoke you are counting. Scope 1 is what you burn yourself. Scope 2 is the electricity you buy. Scope 3 is everything you cause but do not own: your suppliers, your customers' journeys, and for an airport, the planes.
Grid electricity
↓→
Terminal lights
Heathrow buys electricity for its terminals from the grid. Which scope is that?
Scope 1. The lights are inside the airport's own buildings.
Not yet. Scope 1 is fuel the airport burns itself, like gas in its boilers. The lights burn nothing; the power station did, on the airport's behalf.
Scope 2. The airport buys the power; someone else burns the fuel to make it.
Right. Scope 2 is exactly bought electricity. The smoke rises at the power station, but it was made for the airport's lights, so it is counted here.
Scope 3. The power station is a different company.
Not yet. It is a different company, but bought electricity has its own ring, scope 2, because every business buys it and the rules wanted it counted the same everywhere.
Cruise89.3 in 100 · 89%
Take-off and landing6.3 in 100 · 6%
Passengers' journeys to the airport2 in 100 · 2%
Supply chain1.4 in 100 · 1%
Other ground sources0.9 in 100 · 1%
Own boilers and vans0.1 in 100 · 0%
Here is Heathrow's 2025 footprint by scope. Scope 1, its own boilers and vans: a tenth of one in 100. Scope 2, bought electricity: nearly nothing, because it buys power with green certificates. Scope 3: 99 in 100. Inside scope 3, the planes alone are 95.6 in 100 of the whole footprint.
Move the control through what the airport decides to count. Each frame is Heathrow's real 2025 figure for that ring.
Counted0.03 million tonnes
Left out19.4 million tonnes
What is counted: Own boilers and vans
Just scope 1: 26,681 tonnes, a tenth of one in 100 of the whole. This is the smoke the airport makes itself.
Counted0.03 million tonnes
Left out19.4 million tonnes
What is counted: Plus bought electricity
Add scope 2. The electricity is bought with green certificates, so it adds 3 tonnes. Still 0.03 million. Nearly everything is still outside the count.
Counted0.86 million tonnes
Left out18.57 million tonnes
What is counted: Plus the ground: supply chain, vans, journeys
Add every ground source, including passengers' car and train journeys: 0.86 million tonnes counted. The planes are still outside.
Counted2.07 million tonnes
Left out17.36 million tonnes
What is counted: Plus planes taking off and landing
Add aircraft on the runway and climbing away: 2.07 million. Many airports stop counting here.
Counted19.43 million tonnes
Left out0 million tonnes
What is counted: Plus the whole flight out
Add the cruise of every departing flight to its destination: 19.43 million tonnes. Heathrow counts this. The count went up nine times in one step.
Two airports of the same size report footprints of 2 million and 19 million tonnes. What is the most likely reason?
One stopped counting at take-off and landing; the other counted the whole flight out.
Right. The frames show that one step, adding the cruise, multiplies the count by nine. Same planes, same fuel, a different line drawn around what is counted.
One is lying.
Not yet. Both can be honest. The rules let an airport count the cruise or stop at the runway, so long as it says which. The question to ask is where the line was drawn.
One airport's planes are nine times dirtier.
Not yet. No fleet is nine times dirtier than another. A gap that size is a counting choice, not an engine difference.
Move the control.
The airlineflies the plane
↓→
The airportsets the landing fee
There is a reason to count smoke you do not own: you can still move it. Heathrow cannot fly a plane, but it sets the landing fee, and it charges less for cleaner, quieter planes and gives money back for cleaner fuel. Counting scope 3 is how an airport admits the planes are its problem too.
Each is a source of Heathrow's carbon. Which scope does it sit in?
One card at a time. Tap the pile it belongs to.
Card 1 of 6
Gas burned in the boilers that heat Terminal 2
A jet's cruise from Heathrow to New York
Electricity for the baggage belts
Diesel in the airport's own fire engines
A passenger's taxi ride to Terminal 3
Cement in a new taxiway, made by a supplier
Gas burned in the boilers that heat Terminal 2 → Scope 1: own fires
Not yet. Scope 1. The airport owns the boiler, buys the gas and burns it. Its own fire.
A jet's cruise from Heathrow to New York → Scope 3: not owned
Not yet. Scope 3. The airline owns the plane and the fuel. The airport caused the flight to start here but owns none of it.
Electricity for the baggage belts → Scope 2: bought power
Not yet. Scope 2. Bought from the grid; the smoke rose at the power station, for the airport's use.
Diesel in the airport's own fire engines → Scope 1: own fires
Not yet. Scope 1. The airport owns the engines and burns the diesel itself, so it is its own fire.
A passenger's taxi ride to Terminal 3 → Scope 3: not owned
Not yet. Scope 3. The passenger paid the taxi and the taxi burned the fuel. Heathrow counts it because the journey only happened to reach the airport.
Cement in a new taxiway, made by a supplier → Scope 3: not owned
Not yet. Scope 3. The cement works burned the fuel. Heathrow bought the cement, so it caused the smoke without owning the kiln.
Scope 10.1 in 100 of the footprint
Scope 20 in 100 of the footprint
Scope 399.9 in 100 of the footprint
Right. Two own fires, one bought power, three caused but not owned. For an airport, the third pile is not a leftover. It is 99 in 100 of the whole count.
One flight's carbon→Heathrow counts it→The airline counts it→The passenger counts it
One more thing about scope 3: it is shared. The cruise to New York is in Heathrow's footprint, in British Airways' footprint, and in the passenger's. The same tonne is counted three times, once by everyone who could have stopped it. Adding footprints together would count the world's smoke many times over.
1 million tonnesStores and lorries
vsvs
20 million?The food it sells
A supermarket chain says its footprint is 1 million tonnes: its stores and its own lorries. A campaigner says the food it sells, grown and shipped by others, is twenty times that. Who is counting scope 3?
The supermarket. Its lorries are scope 3 because they drive on public roads.
Not yet. The chain owns the lorries and buys their diesel, which makes them scope 1. Where they drive does not change who burns the fuel.
The campaigner. The farms and ships are caused by the supermarket but not owned by it.
Right. Food grown by others for the chain's shelves is scope 3, the same ring as Heathrow's planes. The stores and lorries are scopes 1 and 2.
Both. The two numbers measure the same thing.
Not yet. They do not. One stops at the shop door; the other follows the food back to the field. The gap between them is the whole of scope 3.
Lesson complete
Scope 3 is the carbon you cause but do not own. For an airport it is almost everything.