Assessing Scope 3 Emissions of Airlines: Development and Application of a Calculation Tool

Abstract

The aviation sector faces growing pressure to decarbonize while demand for air travel continues to rise. Although most attention has focused on operational (Scope 1) emissions, a substantial share of the sector’s climate impact occurs upstream and downstream in the value chain (Scope 3 emissions). Despite their importance, these indirect emissions remain poorly understood and inconsistently reported. Several airlines have begun to disclose Scope 3 data, yet the lack of sector-specific guidance and harmonized accounting methods limits transparency and comparability. With the upcoming Corporate Sustainability Reporting Directive (CSRD) set to make Scope 3 reporting mandatory for European companies, including airlines, the need for more consistent and reliable accounting practices is becoming increasingly urgent. This study addresses this gap by mapping key data limitations and emission hotspots in current Scope 3 accounting and by examining how methodological choices affect the reliability of emission disclosure. Building on an Organizational Carbon Footprint (OCF) approach, a Scope 3 assessment tool was developed to operationalize the fifteen categories of the Greenhouse Gas Protocol for the airline context. The tool was applied to two European carriers to test its applicability and to compare results with publicly reported data. Data was gathered from sustainability reports, emission databases, and scientific literature, complemented by expert interviews with professionals from industry and policy. The results show that airlines’ Scope 3 assessments are hindered by unclear system boundaries, reliance on spend-based or aggregated data, and varying calculation methods. These discrepancies illustrate how methodological trade-offs between feasibility, detail, and representativeness shape reported outcomes. The analysis identified major emission hotspots in Downstream Transportation & Distribution, Fuel- and Energy-Related Activities, Purchased Goods and Services, Capital Goods, Business Travel, and Investments. In particular, aviation turbine fuel (well-to-tank) and freight forwarding emerged as key leverage points where small operational changes can lead to disproportionate emission reductions. The findings highlight that greater methodological clarity and harmonized accounting frameworks are essential for ensuring credible, comparable, and actionable Scope 3 emission results. Strengthening boundary definitions and improving supplier engagement can help airlines move beyond estimation toward data-driven climate strategies and more effective decarbonization planning.