Responsible researcher: 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
Intervention Location: Europe
Sample Size: 9 million flights
Sector: Transport Economy
Variable of Main Interest: GHG Emission
Type of Intervention: Operational efficiency
Methodology: Bottom-up
Summary
With the growing debate regarding global warming, greenhouse gas (GHG) emissions have come under great scrutiny from public opinion. Aviation is one of the sectors that causes the most concern in this regard, generating a demand for greater efficiency from sector players. This study evaluated fuel use efficiency and GHG emissions in the aviation sector, using data from intercontinental and intra-European flights. The results found highlighted that a relevant portion of total emissions arises from landing and takeoff procedures. The evidence also highlighted the importance of operational improvement, suggesting that shorter routes (regional and intra-European) are less efficient.
The transport industry plays a central role in global economic growth, being associated with the global integration process experienced in recent decades. However, its rapid expansion has raised environmental concerns. The sector was the only one among Europe's main economic activities to show a continuous increase in greenhouse gas (GHG) emissions between 2013 and 2019, contributing to around a quarter of the European Union's total emissions in 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 an expectation of growth in demand in the medium and long term, combined with the reduction in marginal efficiency gains in aircraft fuel consumption, the discussion regarding the sustainability of the airline sector has gained greater notoriety. Given this scenario, governments and international institutions have set ambitious goals to decarbonize air transport, aiming to achieve net-zero CO2 emissions by 2050.
With the tendency to intensify the adoption of stricter environmental policies, such as carbon pricing mechanisms, several companies have sought to adopt more efficient measures to reduce costs and emissions. The initiatives evaluated include the use of sustainable fuels, technological advances in aircraft, improvements in air traffic management and the adoption of more efficient operational measures. Understanding emissions patterns and identifying variations in fuel consumption efficiency between different types of flights can help develop more effective policies, enabling the sector to continue meeting the demand for air travel without compromising environmental sustainability.
Conventional flight operations are divided into two main phases: activities carried out below 3,000 feet, which include taxi, takeoff, initial climb, approach and landing, and those that occur at higher altitudes, covering climb, cruise and descent. Different factors, such as adverse weather conditions, air traffic restrictions and specific airport regulations, can change the ideal flight profile, influencing the emissions generated at each of these stages. The relationship between the airline sector's capacity to accommodate demand and the technological and operational efficiency of companies 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 cruising altitude, and descent, has traditionally been the focus of research as it represents the majority of total emissions. More recent studies have also begun to analyze emissions generated during landing and takeoff operations (LTO). Although it represents a smaller share of GHGs, emissions generated by LTO directly affect air quality near airports and have implications for human health and local ecosystems.
In the context of intra-European aviation, GHG emissions vary depending on the structure of each country's domestic market and its dependence on air transport. Some markets have higher emissions due to the greater volume of internal flights, while others have a more significant share of cross-border routes. Emissions on international routes within Europe are significant, with some connections between large urban centers concentrating the majority of flights and, consequently, emissions.
Several studies have evaluated these types of emissions at the airport, region or country level, but there are still gaps in the literature regarding fuel consumption efficiency and the variability of emissions patterns between airports and countries on the continent. However, studies that address this issue in an integrated way are still scarce, especially in the European context. This gap reinforces the need to expand analyzes on emissions standards and operational efficiency in the aviation sector.
This study considered the European market to evaluate GHG emissions in aviation. To this end, the authors used a tool developed by the European Environmental Agency (EEA, 2019) to estimate GHG emissions in the aviation sector with detailed observations at flight level. The database used in the study covered commercial passenger flights departing or arriving in Schengen Area countries, in addition to the United Kingdom, Ireland and Turkey, and was obtained from records of scheduled flights. The dataset includes approximately 9 million flights, totaling more than 1.53 billion seats offered. Among these flights, around 6.9 million took place 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. Additionally, average effective taxi times on the ground were incorporated into the analysis to capture variations between airports.
The methodology adopted considered information about origin and destination airports, as well as the aircraft models used. This approach allowed the calculation of fuel consumption and emissions for each flight individually, in addition to analysis segmented by flight phases. Data was aggregated at 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).
The method adopted to estimate fuel consumption and GHG emissions separately considered the takeoff and landing phases (LTO) and the cruise phase (CCD), adopting a bottom-up , as proposed by EEA (2019). Fuel consumption in the LTO phase was determined based on specific engine consumption factors and the time spent in each subphase 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 in relation to the straight-line route.
The main 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 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 between European countries, depending on the volume of air traffic and population density around airports. Therefore, emission levels in different regions, countries and travel destinations (internal and external 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.
Analysis of emissions by flight length revealed that, although long-distance flights represented only around 10.7% of air movements, they were responsible for approximately 60.3% of total GHG emissions. This high impact was 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 around 6.5 times more than an average flight and 15 times more than a short flight.
On the other hand, regional flights had the highest intensity of emissions per kilometer per available seat, due to the lower energy efficiency of regional aircraft and the high incidence of takeoff and landing procedures over short distances. On the other hand, 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 the landing and takeoff cycles (31.5% and 18.6%, respectively), compared to flights medium and long (10.4% and 4.3%, respectively). This was due to high fuel consumption in ground operations and at low altitude, where engine efficiency is reduced. Despite the predominance of emissions during the cruise phase of long-distance flights, the impacts of emissions on the ground and during takeoff were not negligible. Estimates indicated that ground movements at European airports generated around 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 around 102 million tonnes of CO2 in 2019, with an average of 14.72 tonnes per flight and 96.7 kg per available seat. Each country's domestic market strongly influenced total and per capita emissions. Turkey had 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 land 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 investment in high-speed rail infrastructure.
Estimates regarding the spatial distribution of local emissions revealed that the largest volumes of emissions during the LTO phase occurred at airports in the United Kingdom, Germany, Turkey, France and Italy. In per capita terms, island countries such as Malta, Iceland and Cyprus, in addition to Norway, recorded the highest values due to their smaller population 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 from the LTO phase.
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 airline sector has contributed significantly to the increase in emissions, with variations depending on the type of flight, aircraft efficiency and current environmental regulations.
The evidence in this article helps to understand the challenges associated with reducing emissions in the aviation sector, providing support for the formulation of policies aimed at sustainability in air transport. The authors emphasize that, considering the need to reconcile economic growth and reducing environmental impact, improving regulations, encouraging lower-emitting technologies and more efficient flight operations can contribute to mitigating emissions in 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 , vol. 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.
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