Climate Impact by Route & Aircraft

How flight CO₂ is actually measured

Aviation carbon accounting depends on a small number of physical inputs (fuel burn, combustion ratio, atmospheric forcings) and a much larger number of methodology choices (load factor, RFI multiplier, SAF lifecycle treatment, cabin allocation). This calculator surfaces both layers so you can see how each assumption moves the headline number.

Fuel burn: phase model (LTO + climb + cruise + descent)

Block fuel for a single flight is computed as lto + climbKg × lfMult + descKg + cruiseKgHr × cruiseHrs × lfMult × stepClimb, split into a fixed taxi/takeoff/approach cycle (LTO, ICAO EEDB), a fixed climb and descent per aircraft type, and cruise that scales with distance. This is the same phase model used by the route planner's flight-plan card and the Tier 2 emissions breakdown, so all three agree. The cruise rate is pinned so each airframe reproduces its published max-range fuel; short and medium haul read higher because the fixed climb fraction is a larger share of a shorter flight. Stage length over 50 nm is multiplied by a 4% great-circle detour factor for routing inefficiency, the load factor weight multiplier follows IATA RP1726 0.66 + LF × 0.34 (applied to climb + cruise), and a duration-based step-climb credit (up to 4% on long-haul) reflects cruising higher on the cruise segment as the aircraft burns down.

RFI: why one tonne of jet fuel warms more than one tonne of CO₂

Aircraft engines do more than emit CO₂. At cruise altitude (FL280-FL420), nitrogen oxides catalyse ozone production, water vapour persists longer than at the surface, soot acts as ice nuclei, and persistent contrails spread into cirrus that traps outgoing infrared. The Radiative Forcing Index packages all of this into a single multiplier on combustion CO₂. This page uses RFI 2.0 (Lee et al. 2009): about 1.0 from CO₂, 0.52 from NO_x-driven ozone, −0.26 from NO_x-driven methane sink, 0.08 from water vapour, 0.04 from soot, and 0.62 from contrail cirrus. The Lee et al. 2021 effective radiative forcing review suggests the multiplier may be closer to 3.0; ICAO CORSIA disclosures use combustion CO₂ only. Both views matter and the calculator displays both.

SAF: what a 100% blend actually does

Sustainable Aviation Fuel is chemically near-identical to Jet-A in the engine, combustion still produces the same 3.16 kg of CO₂ per kg of fuel burned. The savings come from the lifecycle: feedstock carbon uptake, lower upstream emissions in cultivation and refining. ICAO Doc 10085 (CORSIA Eligible Fuels) approves the HEFA pathway at up to 73% well-to-wake CO₂ reduction, but feedstock-weighted real-world blends average 50-65%. Importantly, SAF does not reduce the non-CO₂ forcings, contrails, NO_x, and water vapour are driven by physical combustion, not by the carbon balance of the fuel. The practical ceiling on RFI-weighted CO₂e reduction at 100% SAF is therefore around 36.5%, not the headline 73%.

Contrail risk: a climatology proxy, not a forecast

The contrail risk badge combines four signals: route midpoint latitude (30-60° mid-latitude jet stream zones and 60-80° polar/sub-polar zones both cross ice-supersaturated regions in the cruise altitude band), season (winter measurably increases ISSR coverage in mid-latitudes), local time of day (nighttime contrails warm two to three times more than daytime contrails because there is no reflective-albedo offset), and engine generation (modern lean-burn combustors like the GE9X, GEnx, Trent XWB, LEAP, and PW1100G emit fewer ice nuclei per kg fuel than legacy CFM56 or CF6 engines). It is a climatology proxy. For real-time per-flight contrail avoidance, see Schumann's CoCiP and ECMWF IFS ISSR forecasts; both go beyond what a static client tool can compute.

Per-passenger allocation: floor area, not seat count

Cabin-class CO₂ uses the IATA floor-area method. Total flight CO₂e is divided across cabins weighted by relative floor area: economy 1.0, premium economy 1.7, business 2.7, first 4.2. Multiplied by the occupied-seat count in each cabin (base seats × class load factor) so the per-economy-pax number represents an actual passenger's share, not a fictional per-available-seat figure. A long-haul business seat therefore carries roughly 2.7× the per-economy CO₂e on the same flight, which is consistent with how IATA, ICAO, and the major carbon-disclosure frameworks allocate.

Mode comparison: like-for-like per passenger-km

Car, EV, and rail comparators are expressed per passenger-kilometre, so a single multiplication by distance gives a fair side-by-side. Car uses 0.114 kg CO₂/pkm (EEA fleet average at 1.5 occupancy), EV uses 0.035 kg/pkm (US grid average at 1.5 occupancy), and intercity rail uses 0.035 kg/pkm (EEA EU intercity). Note that flight values here include RFI while ground modes do not, flight has no clean ground-mode peer for the contrail and high-altitude NO_x components. Stripping RFI brings per-pax flight CO₂ closer to a 1.5-occupant gasoline car.