A baseline is a year you chose
- In the air15 in 100 lowerOn the ground45 in 100 lowerThan 2019the baseline
Picture Heathrow's two promises for 2030. Carbon in the air: at least 15 in 100 lower than 2019. Carbon on the ground: at least 45 in 100 lower than 2019. Both say the same small words: than 2019. That year is doing a lot of work.
- 201920 million tonnes in the air202214.3 million tonnes in the air202317.9 million tonnes in the air202418.5 million tonnes in the air202518.6 million tonnes in the air
The year you compare against is called the baseline. A target is a cut measured from it. Heathrow picked 2019: its busiest year before Covid, flown on an older fleet than today's. Its goal is that 2019 turns out to be its year of peak carbon. Measured from a peak, every year since looks like progress.
- 2019 baseline20 million tonnes2030 target17 million tonnes
In the air, 2019 was 20.0 million tonnes. The 2030 target is 15 in 100 below that. What is the target, in million tonnes?
million tonnesTake 15 in 100 of 20 away from 20.
Right. 17.0 million tonnes. Heathrow's own target line is 17,004,645 tonnes. In 2025 the figure was 18.6 million, so about half of the cut has arrived, five years in. Move the control to change the baseline year. The 2025 figure never changes: 18.6 million tonnes in the air. Watch what the story does.
Baseline year20 million tonnes202518.6 million tonnesBaseline year: 2019
Against 2019, 20.0 million: 2025 is 7 in 100 lower. Heathrow's chosen baseline, and the story is progress.
Baseline year14.3 million tonnes202518.6 million tonnesBaseline year: 2022
Against 2022, 14.3 million, the Covid recovery year: 2025 is 30 in 100 higher. Same airport, same 2025, and the story is now growth.
Baseline year17.9 million tonnes202518.6 million tonnesBaseline year: 2023
Against 2023, 17.9 million: 2025 is between 3 and 4 in 100 higher.
Baseline year18.5 million tonnes202518.6 million tonnesBaseline year: 2024
Against 2024, 18.5 million: 2025 is about level, up less than 1 in 100.
Same 2025 count, four baselines. Which sentence is true?
All four readings are true. The baseline decides whether 2025 reads as a cut or a rise.
Right. Nothing in 2025 changed between frames. A target is a comparison, and a comparison has two ends. Whoever picks the other end picks the story.The 2022 reading is false; carbon cannot have risen 30 in 100.
Not yet. It did. Flights came back after Covid. The frame is Heathrow's own figures, 14.3 then 18.6. A baseline in a quiet year makes a recovery look like a surge.Only the 2019 reading is true, because 2019 is the official baseline.
Not yet. Official means chosen, not truer. The 2022 reading is just as real a count; it simply compares with a quieter year.Move the control.
- about the same as 2019Flights7 in 100 lowerCarbon in the air
A baseline is not a trick. Every target needs one, and 2019 is a fair choice: the last normal year. But notice what it means. Flights in 2025 roughly matched 2019, and carbon was 7 in 100 lower. So far the cut has come from newer planes, not from fewer flights.
Two targets, two scores so far. Tap the one that is furthest from its target.
Tap the part of the picture that answers it.
In the air: 7 of 15 done7 in 100 cut so farOn the ground: 18 of 45 done18 in 100 cut so farOn the ground: 18 of 45 done
Right. Eighteen cut, forty-five promised, 27 still to find. Heathrow's own status for it is more work to do. The supply chain is rising because the airport is building more.In the air: 7 of 15 done
Not yet. Seven of fifteen, about half way with five years left. Heathrow marks this one on track. It is the smaller gap, though the bigger tonnage.- More buildingMore concrete and steelSupply chain carbon up 16 in 100Ground target harder
Heathrow marks each target with a status word: on track, or more work to do. In the air is on track. On the ground is more work to do, because the biggest ground source still rising is the supply chain: the concrete, steel and services of everything it builds. The more it builds, the harder that target gets.
By 2030, Heathrow wants carbon on the ground 45 in 100 below 2019. In 2025 it was 18 in 100 below. How far through the time is it, 2019 to 2030?
Pick one. Nothing is scored.
Time gone, in 10055Cut made, in 100 of the target40About half.Six of eleven years, a little over half. Under half the cut, with over half the time gone, is what more work to do means in numbers. Guesses tend to land late, because 2019 feels recent.- 2020lockdown yearDown 30 in 100since then
A council says its carbon is down 30 in 100 since 2020. A resident points out that 2020 was the lockdown year. What has the resident spotted?
Nothing. Any baseline is as good as any other.
Not yet. The frames in this lesson showed the same 2025 reading as a 7 in 100 cut and a 30 in 100 rise. A baseline changes the story, which is why it matters which one was picked.The baseline is a quiet year, so a return to normal reads as a cut.
Right. Lockdown emptied the roads. Measured from that year, even a rise back to normal can look like a fall. The same number against 2019 might read very differently.The council has made an arithmetic error.
Not yet. The sum may be perfectly right. The question is not whether 30 is correct but what it is 30 in 100 of. A baseline is a choice, not a mistake.
Lesson complete
A target is a cut from a baseline. Change the year, and the same number tells a different story.