Principal investigator: Bruno Benevit
Original title: Pathways toward sustainable aviation: Analyzing emissions from air operations in Europe to support policy initiatives
Author: Nicolò Avogadro and Renato Redondi
Location of the Intervention: Europe
Sample Size: 9 million flights
Sector: Transportation Economics
Primary Variable of Interest: GHG Emissions
Type of Intervention: Operational efficiency
Methodology: Bottom-up
Summary
With the growing debate regarding global warming, greenhouse gas (GHG) emissions have been under intense public scrutiny. Aviation is one of the sectors that most raises concerns in this regard, generating a demand for greater efficiency from industry stakeholders. This study evaluated fuel efficiency and GHG emissions in the aviation sector, using data from intercontinental and intra-European flights. The results highlighted that a significant portion of total emissions stems from landing and takeoff procedures. The evidence also emphasized the importance of operational improvements, suggesting that shorter routes (regional and intra-European) are less efficient.
- Policy Problem
The transportation industry plays a central role in global economic growth, being associated with the process of global integration experienced in recent decades. However, its rapid expansion has generated environmental concerns. The sector was the only one among the main economic activities in Europe to show a continuous increase in greenhouse gas (GHG) emissions between 2013 and 2019, contributing to about a quarter of the total emissions of the European Union during that period (AVOGADRO; REDONDI, 2024). Although land transport represents the largest share of these emissions, air transport has stood out as one of the main sources of concern due to its accelerated growth. Since 1990, aviation emissions have more than doubled.
With the expectation of increased demand in the medium and long term, coupled with reduced marginal efficiency gains in aircraft fuel consumption, the discussion regarding the sustainability of the aviation sector has gained greater prominence. In this context, governments and international institutions have established ambitious targets for decarbonizing air transport, aiming to achieve net-zero CO2 emissions by 2050.
With the increasing trend towards the adoption of stricter environmental policies, such as carbon pricing mechanisms, several companies have sought to adopt more efficient measures aimed at reducing costs and emissions. Among the initiatives evaluated are the use of sustainable fuels, technological advancements in aircraft, improvements in air traffic management, and the adoption of more efficient operational measures. Understanding emission patterns and identifying variations in fuel consumption efficiency between different types of flights can help in the development of more effective policies, enabling the sector to continue meeting the demand for air travel without compromising environmental sustainability.
- Policy Implementation Context
Conventional flight operations are divided into two main phases: activities performed below 3.000 feet, which include taxiing, takeoff, initial climb, approach, and landing; and those that occur at higher altitudes, encompassing climb, cruise, and descent. Different factors, such as adverse weather conditions, air traffic restrictions, and specific airport regulations, can alter the ideal flight profile, influencing the emissions generated in each of these stages. The relationship between the aviation sector's capacity to accommodate demand and the technological and operational efficiency of airlines and airports is also a relevant aspect for evaluating emissions.
In this context, the environmental impact of aviation has been increasingly studied to improve the understanding of its GHG emissions. The cruise phase of flight (CCD), which includes climb, flight at cruise altitude, and descent, has traditionally been the focus of research, as it represents the largest share of total emissions. More recent studies have also begun to analyze emissions generated during land-to-takeoff (LTO) operations. Although representing a smaller share of GHGs, emissions generated by LTO directly affect air quality in the vicinity of airports and have implications for human health and local ecosystems.
In the context of intra-European aviation, GHG emissions vary according to the structure of each country's domestic market and its dependence on air transport. Some markets have higher emissions due to a greater volume of domestic flights, while others have a more significant share of cross-border routes. Emissions on international routes within Europe are significant, with some connections between major urban centers concentrating the majority of flights and, consequently, emissions.
Several studies have evaluated these types of emissions at the airport, regional, or national level; however, gaps remain in the literature regarding fuel consumption efficiency and the variability of emission patterns between airports and countries on the continent. Furthermore, studies addressing this issue in an integrated manner are still scarce, especially in the European context. This gap reinforces the need to expand analyses of emission patterns and operational efficiency in the aviation sector.
- Evaluation Details
This study considered the European market to assess GHG emissions in aviation. To this end, the authors used a tool developed by the European Environment Agency (EEA, 2019) to estimate GHG emissions in the aviation sector with detailed observations at the flight level. The database used in the study covered commercial passenger flights departing from or arriving in countries within the Schengen Area, as well as the United Kingdom, Ireland, and Turkey, and was obtained from scheduled flight records. The dataset includes approximately 9 million flights, totaling more than 1,53 billion seats offered. Of these flights, approximately 6,9 million occurred within Europe, corresponding to 76,7% of the total, with 1,05 billion seats offered.
Given the significant impact of the COVID-19 pandemic on the sector in 2020 and 2021, and the still incomplete recovery in 2022, the year 2019 was selected as a reference. To estimate fuel consumption and emissions generated during landing and takeoff procedures, specific data on fuel consumption by aircraft type and flight phase were used, based on information about engines and their efficiency. In addition, average effective taxi times on the ground were incorporated into the analysis to capture variations between airports.
The methodology adopted considered information on origin and destination airports, as well as the aircraft models used. This approach allowed for the calculation of fuel consumption and emissions for each flight individually, in addition to segmented analysis by flight phases. The data were aggregated at the airport and country levels. The methodology also considered the impact of operational factors, such as route deviations, holding procedures, and fragmentation of European airspace, which affect air traffic efficiency. Studies indicate that these inefficiencies increase fuel consumption by between 6% and 12%, given that aircraft rarely follow direct trajectories between origin and destination airports (AVOGADRO; REDONDI, 2024).
- Method
The method adopted to estimate fuel consumption and GHG emissions considered the takeoff and landing (LTO) phase and the cruise phase (CCD) separately, adopting an approach bottom-up, as proposed by the EEA (2019). Fuel consumption in the LTO phase was determined based on specific engine consumption factors and the time spent in each sub-phase of the cycle. For the CCD phase, consumption was estimated taking into account the type of aircraft and the distance between the origin and destination airports.
Emissions were expressed in CO2 equivalents and include not only carbon dioxide, but also methane and nitrous oxide, weighted according to their global warming potential. Furthermore, to reflect inefficiencies in the actual flight path, a model was used that adjusts the distance actually traveled relative to the straight-line route.
The primary analysis of emissions based on flight length categorized routes into four groups: regional (less than 500 km), short-haul (between 500 and 1500 km), medium-haul (between 1500 and 4000 km), and long-haul (more than 4000 km). To understand the heterogeneity of how GHG emissions occur in aviation operations, the authors estimated the impacts in the CCD and LTO phases, and in their different components.
The spatial distribution of emissions generated during the LTO cycle varies among European countries, depending on the volume of air traffic and the population density around airports. Therefore, emission levels in different regions, countries, and travel destinations (domestic and international flights) were also considered. Finally, the authors presented the calculation of per capita emissions in order to understand the relative impact of these emissions in each country.
- Main results
Analysis of emissions by flight length revealed that, despite long-haul flights representing only about 10,7% of air traffic, they were responsible for approximately 60,3% of total GHG emissions. This high impact occurred due to the higher emissions per flight and per seat available in this segment. On average, a long-haul flight emitted 210,4 tons of CO2, resulting in approximately 700 kg per seat. Comparatively, a long-haul flight pollutes about 6,5 times more than an average flight and 15 times more than a short flight.
On the other hand, regional flights showed the highest intensity of emissions per kilometer per available seat, due to the lower energy efficiency of regional aircraft and the high incidence of short-distance takeoff and landing procedures. In contrast, medium-haul flights proved to be the most environmentally efficient segment, possibly due to the balance between aircraft efficiency and distance traveled.
The distribution of emissions by flight phase showed that regional and short-haul flights had a significantly higher incidence of emissions during landing and takeoff cycles (31,5% and 18,6%, respectively), compared to medium and long-haul flights (10,4% and 4,3%, respectively). This was due to high fuel consumption during ground operations and low altitude, where engine efficiency is reduced. Despite the predominance of emissions during the cruise phase in long-haul flights, the impacts of emissions on the ground and during takeoff were not negligible. Estimates indicated that ground movements at European airports generated approximately 8,65 million tons of CO2 annually, with more than half of these emissions concentrated in the 17 busiest airports in the region.
In the context of intra-European flights, total emissions were estimated at approximately 102 million tons of CO2 in 2019, with an average of 14,72 tons per flight and 96,7 kg per available seat. Each country's domestic market strongly influenced total and per capita emissions. Turkey presented the highest absolute emissions, followed by Spain, Italy, France, Germany, and the United Kingdom. When considering per capita emissions, Norway stood out with the highest values due to its dependence on air transport and the frequent use of less efficient regional aircraft. According to the authors, the transition to electric aircraft was identified as a viable solution to reduce the environmental impact of regional and domestic flights in markets with few ground transport alternatives. For international flights within Europe, connections between Spain, the United Kingdom, and Germany represented the most polluting routes, highlighting the need for coordinated initiatives to mitigate emissions from these routes, including investments in high-speed rail infrastructure.
Estimates regarding the spatial distribution of local emissions revealed that the largest emission volumes during the LTO phase occurred at airports in the United Kingdom, Germany, Turkey, France, and Italy. In per capita terms, island nations such as Malta, Iceland, and Cyprus, as well as Norway, recorded the highest values due to their smaller populations and greater dependence on air transport. Turkey and the United Kingdom stood out for having a high proportion of emissions associated with taxiing, representing approximately 40% of total emissions during the LTO phase.
- Lessons in Public Policy
In this article, the authors analyzed the relationship between the growth of air transport and greenhouse gas emissions, considering different factors that influence this dynamic. The results indicate that the expansion of the aviation sector has contributed significantly to the increase in emissions, with variations according to the type of flight, the efficiency of the aircraft, and the current environmental regulations.
The evidence presented in this article helps to understand the challenges associated with reducing emissions in the aviation sector, providing input for the formulation of policies aimed at sustainability in air transport. The authors emphasize that, considering the need to reconcile economic growth and the reduction of environmental impact, improving regulations, encouraging lower-emission technologies, and more efficient flight operations can contribute to mitigating emissions from the sector.
References
AVOGADRO, N.; REDONDI, R. Pathways toward sustainable aviation: Analyzing emissions from air operations in Europe to support policy initiatives. Transportation Research Part A: Policy and Practice, v. 186, p. 104121, Aug. 2024.
EEA. Transport: Increasing Oil Consumption and Greenhouse Gas Emission Hamper EU Progress Towards Environment and Climate Objectives. [sl] European Environment Agency, 2019.
