Estimating passenger emissions from airfares supports equitable climate action

Abstract

Air travel generates a substantial and growing share of global greenhouse gas emissions. Reduction efforts partly rely on estimates of emissions per passenger, which may be used for carbon budgets, offsets, or taxes. Aircraft emissions are typically allocated to individual passengers through space-based allocation dependent on seating arrangements by travel class. However, the operation of aircraft depends on profitability, which benefits from high fares from late bookings, often by business and high-income travellers. Fare-based allocation recognises the economic drivers of airline emissions by allocating the aircraft emissions proportionally to the paid airfares. In this article, we compare space-based passenger emissions, which differ only by class, with fare-based passenger emissions, which depend on the fare paid by the individual traveller. We extract space-based allocation factors from widely used emission calculators and derive fare-based allocation factors from airfares for domestic travel in the US. We find that the space-based allocation factors reflect the difference in average expenditure by travel class but not the difference in expenditure between travellers. With fare-based accounting, the most expensive economy trips have similar emissions to space-based premium trips, while less expensive premium trips have similar emissions to space-based economy trips. We find that a tax on fare-based instead of space-based emissions leads to a more evenly distributed impact on low-fare and high-fare travellers whilst achieving the same reduction in airline revenues. We conclude that fare-based emissions accounting better reflects the drivers of airline emissions and supports more equitable climate action.