What Does a Below-Average CO2 Label on a Flight Mean? Route-Relative Emissions Labels, Per-Passenger Allocation Rules and US Aviation Fuel and CO2 from Published Methodologies, BTS and EPA Data, 1990–2025

Flight search pages now label fares as having lower, typical or higher emissions, but the reference against which a flight is judged is rarely stated. We document the rule and put numbers on the quantities around it using public methodologies and official statistics. The label compares a flight's estimated CO2e per passenger with a day-weighted median of up to 20 routes serving the same market; in the published example a flight estimated at 84 kg is marked below the typical 90 kg. Applying the Travel Impact Model 3.0.0 method to one Boeing 787-9 with a fixed layout, an economy seat came to 76.0 kg of CO2e from well to wake at 500 nautical miles and 606.0 kg at 5,500 nautical miles, 7.97 times as much for 11 times the distance; seat-area weights raised a business seat to 4 times and a first-class seat to 5 times economy on a wide-body aircraft. Whole-aircraft fuel from the ICAO calculator showed newer narrow-bodies burning 16% less than their predecessors at 2,000 nautical miles. US reference factors gave 0.207 kg of CO2 per passenger-mile for flights under 300 miles against 0.129 kg for 300–2,300 miles. US air carriers burned 20.47 billion gallons of jet fuel in 2025, the highest value since 1990, after a 2020 low of 11.48 billion. Commercial aircraft emitted 130.8 million metric tons of CO2e within the United States in 2023, 18% more than in 1990, and international departures a further 63.5 million metric tons of CO2 in 2022. All inputs are public.