Primary sources · 4
- [1] DESNZ 2024 condensed factors — kg CO₂e per passenger-km by distance band and cabin class · UK gov.uk · June 2024 https://assets.publishing.service.gov.uk/media/6722566a3758e4604742aa1e/ghg-conversion-factors-2024-condensed_set__for_most_users__v1_1.xlsx
- [2] DESNZ 2024 methodology paper — How each factor is derived, including the cabin allocation rationale · UK gov.uk · June 2024 https://assets.publishing.service.gov.uk/media/66a9fe4ca3c2a28abb50da4a/2024-greenhouse-gas-conversion-factors-methodology.pdf
- [3] Lee et al. (2021) — The radiative-forcing science behind the 1.9 × uplift · Atmospheric Environment 244, 117834 · January 2021 https://doi.org/10.1016/j.atmosenv.2020.117834
- [4] UK National Travel Survey 2023 — Source for the UK per-capita aviation emissions comparator · Department for Transport · 2024 https://www.gov.uk/government/statistics/national-travel-survey-2023
AirMilesCalc converts a great-circle distance into a kg CO₂e number in five steps: classify the distance band, pick the base factor, apply the cabin multiplier, apply the radiative-forcing uplift, and convert to comparators. This page walks the full pipeline with a single worked example so every number can be checked.
The five-step pipeline
- 1Compute great-circle distance
Vincenty inverse on WGS-84 returns the surface distance in metres, rounded to a whole kilometre on output. For LHR → JFK we get 5,555 km.
- 2Classify the distance band
Our internal bands match DESNZ: short-haul (under 1,500 km), medium-haul (1,500 – 4,000 km), long-haul (over 4,000 km). LHR → JFK at 5,555 km is long-haul. The base factor is 0.150 kg CO₂e per pax-km.
- 3Apply the cabin multiplier
Economy = 1.00 ×, premium economy = 1.60 ×, business = 2.90 ×, first = 4.00 ×. For economy LHR → JFK: 5,555 × 0.150 × 1.00 = 833 kg CO₂e per passenger one-way.
- 4Document the radiative-forcing uplift
The 0.150 figure already includes the DESNZ 1.9 × multiplier — the underlying CO₂-only number is 0.150 / 1.9 ≈ 0.079 kg per pax-km. We surface both kg CO₂ and kg CO₂e in the output so users can choose their reporting basis.
- 5Generate comparators
Trees needed = ceiling(kg CO₂e / 21), where 21 kg/year is the midrange of a mature broadleaf temperate tree's annual sequestration. Personal carbon-budget comparators draw on the UK National Travel Survey baseline of ~12 tonnes CO₂e per capita.
Worked example: London → New York return
| Cabin | Distance (return km) | Factor × cabin mult. | kg CO₂e | Trees / year |
|---|---|---|---|---|
| Economy | 11,110 | 0.150 × 1.00 | 1,667 | 80 |
| Premium economy | 11,110 | 0.150 × 1.60 | 2,666 | 127 |
| Business | 11,110 | 0.150 × 2.90 | 4,832 | 231 |
| First | 11,110 | 0.150 × 4.00 | 6,666 | 318 |
The four-row difference is striking: a first-class round-trip on the same flight emits 4 × what an economy round-trip does, because the four seats consume 4 × the floor area. Operationally, the aircraft burns identical fuel regardless of who sits where. The cabin number is an allocation choice rather than a physical measurement — it answers the question "if everyone in this cabin paid the same per-square-metre rate for the trip, what is my share?"
Where the comparators come from
We turn the kg CO₂e number into three comparators because raw kilograms are abstract. Trees per year assumes a mature broadleaf temperate tree absorbs 21 kg CO₂ per year — a midrange figure from published forest- sequestration studies, intentionally conservative. Driving km equivalent uses 0.21 kg CO₂e per car-km from DESNZ's 2024 average UK passenger-car factor. Personal carbon-budget months uses 12 tonnes CO₂e per capita per year as the UK baseline.
| Comparator | Value | Source |
|---|---|---|
| kg CO₂ absorbed per mature tree per year | 21 | Midrange of published estimates |
| kg CO₂e per average UK car-km | 0.21 | DESNZ 2024 passenger car |
| kg CO₂e per average UK household kWh | ≈ 0.21 | DESNZ 2024 grid average |
| tonnes CO₂e per UK capita per year | ≈ 12 | UK NTS / Carbon Trust 2024 |
| IPCC 1.5 °C-compatible per-capita target by 2030 | ≈ 2 | IPCC AR6 WG3 illustrative |
What we deliberately do not include
The base DESNZ factor is tank-to-wake — the emissions from burning fuel in flight only. We do not add the 1.2 × well-to-tank uplift for fuel extraction and transport because most corporate reporting frameworks treat well-to-tank as a separate Scope 3 category. We also do not model real-world load factor or fleet-specific efficiency; the published DESNZ number is already a UK-fleet weighted average.