Airports—Energy and Sustainability Perspectives

Abstract

This study explored the role of airports in the aviation sector from both energy and sustainability perspectives, highlighting their potential contribution to reducing the sector’s carbon emissions. The methodology involved a literature review and a questionnaire distributed to both airports and aviation organizations. The results from these approaches indicated varying focuses on tackling the subject. The literature review results indicated a clear preference in the papers for SAF solutions over the development of more environmentally friendly airports. Adoption of 100% SAF in aircraft is still in its early stages of development and can be considered a long-term goal because it requires heavy engineering intervention and alteration of aircraft engines. The transition of airports’ infrastructures, on the other hand, can be visualized as a feasible and attainable goal and hence should be considered a short-term goal to attain. Many airports, including respondents to the questionnaire, have already worked on their infrastructure; however, they also expressed concerns about the lack of enabling policies and incentives. Other action steps, such as close collaborations among stakeholders, enhancing research and development, and government support, were also seen as significant for establishing greener airports. The literature results indicate a major research gap in a significant integral part of the aviation sector (i.e., greener airports). It is therefore important that member states collaborate and work closely with key organizations such as ICAO, IATA, and the UN through the latter’s Sustainable Development Goals (SDGs) to breach this research gap and establish more sustainable airports in the near future.

1. Introduction

1.1. Background

Like many other industries, the aviation sector is under growing pressure to reduce its carbon footprint and take action against climate change. However, energy-intensive airplanes are not the only contributor to this problem. Today, as airports expand, so do their carbon emissions, because more energy is required to power new terminals, ground support vehicles, and the buildings make up the airport’s infrastructure [1].

Long before the Wright brothers perfected the first flying plane in 1903, many earlier trials were conducted [2], from the ancient Greeks (B.C.) to the Andalusian scholar Ibn Firnas in the 9th century A.D. and thereafter the Italian scientist Giovanni Alfonso in the 17th century, followed by the German engineer Otto Lilienthal’s fatal flight attempt in 1896, and lastly to the Wright brothers in the 20th century [3]. Today and after more than 100 years of development in the aviation sector, this has now become one of the most “global” industries, connecting people, cultures, and businesses across continents [4]. The sector is immense and regarded as one of the most rapidly expanding industries. In 2018 alone, airlines worldwide carried around 4.3 billion passengers annually and 58 million tons worth of freight, equivalent to more than 100,000 flights per day and around USD 18 billion worth of goods [4].

Although aircraft are the most visible part of the industry, it is important to understand that the sector is more than just these flying structures and that the sector’s growth and decline can be measured using multiple metrics. These may include aircraft manufacturers, services accompanying the aircraft, and related infrastructure on the ground, along with suppliers of spare parts. The industry encompasses both goods and services centered on aircraft [2].

To promote the safety and orderly development of international civil aviation worldwide, a specialized agency of the United Nations, the International Civil Aviation Organization (ICAO), was established [4]. Since its establishment in 1944, the ICAO has worked constantly to address and support global aviation safety through the following coordinated areas:

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Policy and standardization.

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Monitoring safety trends and indicators.

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Safety analysis.

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Implementing programs to address safety issues [4].

The International Air Transport Association (IATA) is another significant body of the aviation industry. This trade association for the world’s airlines represents approximately 290 airlines (equivalent to 82% of total air traffic) [5]. The key responsibilities of the IATA involve supporting the interests of airlines across the globe and raising awareness of the benefits that aviation brings to national and global economies. The means of achieving this include easing border crossing through the use of border control technologies, principles, and processes, all of which provide more open, yet secure schemes to enhance trade, travel, and tourism, and hence national economies [5].

1.2. Carbon Emissions

Carbon dioxide (CO₂) constitutes the largest share of manmade greenhouse gas emissions. The effect of this added CO₂ emission to the atmosphere is detrimental because it disturbs Earth’s radiative balance. In effect, this leads to an increase in the Earth’s surface temperatures and consequently has direct negative impacts on climate, sea levels, and world agriculture [6].

Although flying is one of the most carbon-intensive activities, it contributes only 2.5% of the world’s carbon emissions. This is because most people do not fly. According to previous studies, only 10% of the world’s population flies in most years [7]. However, this percentage is actually increasing and is anticipated to grow rapidly within a few years.

To understand how this increase is developing, it is crucial to understand how carbon emissions within the sector are calculated. The following three metrics were considered in the calculations:

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Aviation demand: The magnitude of passengers and freight flown in kilometers.

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Energy efficiency: The amount of energy being used per kilometer.

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Carbon intensity: Different fuels’ yield to different rates of emitted carbon per unit of energy.

The size of carbon emissions (CO₂) is calculated as: aviation demand × energy efficiency × carbon intensity.

Therefore, an increase in any of these three metrics would result in an increase in carbon emissions. Today and in comparison to the last few decades, it is clear that more people are flying and more goods are being transported by air. According to previous studies, passenger and freight demands quadrupled between 1990 and 2019 [7]. Simultaneously and in comparison to three decades ago, flying has become more than twice as energy-efficient. This is attributed to improved design and technology. Currently, larger planes carry more loads, whether passengers or freight. However, one metric that has not changed at all is carbon intensity. This is not surprising, because the jet fuel used in the 1990s is the same as that used today. Although biofuels and other alternatives are slowly seeking to expand in the aviation market, they still account for a very small fraction of the sector’s demand [7]. Referring back to the metrics and CO₂ equation mentioned earlier, it becomes self-explanatory why CO₂ emissions continue to grow in the sector. In simple math, having a quadrupled demand, constant carbon intensity, and doubled energy efficiency yields a doubling in CO₂ emissions. The statistics and trends shown in Figure 1 confirm this. This shows how the sector’s carbon emissions have grown over the decades (from the 1940s to 2019) [7].

According to the International Energy Agency, CO₂ emissions from the sector have grown faster in recent decades than rail, road, or shipping, and reached almost 800 Mt in 2022. This was approximately 80% of the pre-pandemic level [8]. Today, the ICAO is responsible for addressing international aviation emissions. In 2016, members of the ICAO agreed and decided to create a global market-based mechanism for aviation emissions, called the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). One main aim of the CORSIA mechanism was to offset any growth in international aviation CO₂ emissions above the 2019 levels. Offsetting emissions targets operators through the purchasing and canceling of emission units, with one unit being equivalent to 1 ton of CO₂ emissions being removed or avoided from the atmosphere [9].

With international aviation pre-pandemic growth reaching up to 4% per annum, various approaches and proposals were considered by CORSIA; however, the most popular approach was the use of sustainable aviation fuels (SAFs). CORSIA allows the use of SAFs (e.g., a drop in alternative jet fuels) to reduce the carbon offsetting requirements of airlines. In fact, to be eligible for ICAO CORSIA, a CORSIA eligible fuel (CEF) must meet the sustainability criteria. Fuel is defined as having life-cycle GHG emissions that are at least 10% below the baseline of petroleum jet fuels and are not produced from biomass obtained from land with a high carbon stock [10].

By 2024, 126 member states had joined and were participating actively in CORSIA [11]. It is estimated that CORSIA’s offset will contribute up to 19% of the emission reductions needed by 2050. According to Michael Schneider, IATA’s assistant director of aviation environment, huge investments in new technologies, especially sustainable aviation fuels (SAFs), will play a key role in achieving the CO₂ reduction target for the year 2050. He added, “Moreover, the right offsets are not about compensation for emissions but about contributing to emission reduction with many of the offset projects offering socio-economic co-benefits for local communities” [12].

1.3. Sustainable Aviation Fuels (SAF)

Although sustainable aviation fuel is considered one of the key pathways for CORSIA, it is still used in limited quantities. As of 2022, less than 1% of all European flight operations were being operated on SAF. This low utilization rate is attributed to both availability and cost [13].

To understand why SAF is being considered and what kinds of challenges it faces today, it is important to recognize how this fuel can be produced. Two main categories form the SAF feedstock. One is from biogenic feedstocks such as crops, vegetable oils and fats, and agricultural and non-agricultural residues, and the other is from non-biogenic resources such as waste gases and hydrogen [14]. There are several characteristics that any chosen SAF type must possess to be effectively implemented. This includes the competitiveness of the fuel from technical, economical, and environmental perspectives, along with the level of abundance of the resource from which the fuel is made [15].

The significance of SAF adoption does not stem from its combustion levels in aircraft engines because it is nearly the same as conventional kerosine-based jet fuels, but it is the potential for CO₂ savings that make the difference. This is determined by life-cycle analysis of the feedstocks used as raw materials and the required production and conversion processes. With the understanding that there are several pathways to produce SAF through different feedstocks, this suggests that there will be varying conversion processes and certainly different associated production costs for each SAF type [13]. Generally, for the purpose of this study, it is important to recognize that the production of SAF is still more expensive than fossil-based jet fuel [13]. Moreover, the infrastructure and supply chains for efficient large-scale production of SAF are still in their early stages [14]. According to the European Union Aviation Safety Agency (EASA), a few other challenges facing the adoption of SAF today include the following:

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Acquiring fuel approvals from the authorities: This can be both a lengthy and costly process.

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Availability of feedstock to sustain long-term supply [16].

One unique SAF pathway, however, that helps tackle the aforementioned barriers comes from the “drop in fuels” approach. Certified SAFs are blended with kerosine for use in current aircraft engines. Not only does this fit in with the present jet engines (i.e., no change in aircraft design required) but it has also helped SAFs to be more cost-effective [13].

1.4. Airports

Today, airports consist of landside facilities such as terminals that provide passenger services and airside ground facilities, which include the runway, taxiway, and gates, all of which serve arriving and departing aircraft [17]. Figure 2 provides a generic overview of an airport with both air- and landsides represented [18].

With the growing demand for air travel, the operations and resources of these facilities have intensified, making efficient management a necessity [17].

Unlike other facility complexes, airports have economic, environmental, and social impacts on communities [19]. While it is important for these complex infrastructures to satisfy the expected traffic demand over time, they must also consider their level of environmental effect to provide such services [20].

One of the key services investigated and discussed in this study is airport operations. The significance of such services lies not only in identifying and shaping how airports operate, but more importantly in reflecting the anticipated sustainability impacts on the airport and its surroundings. Airport operations are typically divided into two types: airside and landside operations. The airside is the area where the movement of the aircraft and ground-handling services are the most active. This includes the areas around the runway, ramps, and airfields. Airside operations primarily involve takeoff and landing of aircraft and turnaround time activities [17].

The turnaround time (TAT) is basically the fundamental component of airports’ airside operations, since this involves several activities from the moment the aircraft reaches its parking position after landing until it is enabled to take off for a new flight [17]. The key points to mention include the following:

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Providing power supply to the aircraft through a ground power unit (GPU).

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Connecting a preconditioning air unit (PCA) during summer seasons for cooling and ventilation of aircraft.

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Connecting an airbridge and/or a staircase for the passengers to exit/enter the aircraft.

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Transporting passengers to and from the aircraft to the airport terminals.

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Unloading and loading of aircraft baggage and cargo using belt or cargo loaders.

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Supplying potable water and removing lavatory waste water from the aircraft using water trucks.

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Refueling of aircraft using a fuel truck.

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Cleaning of aircraft interior.

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Providing catering supplies [21].

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In cases of cold weather conditions, deicing of aircraft to remove surface frost, ice, or frozen contaminants.

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Pushback operations, which involve pushing aircraft away from gates/parking positions in preparation for taxiing to the runway for departure. The procedure requires a specialized ground vehicle typically attached to the front wheel of the aircraft (see Figure 3a,b).

To complete the key activities mentioned above, considerable resources and utilization of operators and equipment are required [21].

For the purpose of this study, the focus is on accounting for the ground handling equipment being used and how these may contribute to the sector’s carbon footprint.

Although many studies have been published on the airside, landside operations and infrastructure are equally crucial when addressing sustainability and environmental impacts. The landside area includes parking lots, fuel tank farms, and access roads and extends to the properties surrounding the airport [23].

Typical operations that form this part of the airport include the following.

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Management of passenger buildings and terminals: Managing everything from the check-in counters to security checkpoints.

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Customer service delivery: Catering passengers needs within airports’ hotels, lounges, and other facilities.

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Management of parking operations: Monitoring and controlling the overall traffic surrounding the airport. This primarily entails the transportation of passengers from parking lot areas and bus stations to the airport.

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Security and safety operations: Maintaining a safe and secure environment for both passengers and staff. Patrolling and surveillance of airport infrastructure and surrounding areas (e.g., parking lots) are typical activities performed to enhance this crucial operation [23].

Yet again and similar to airside operations here too, there is a requirement for equipment, manpower, and even infrastructure to perform the activities in a safe and secure manner.

Airports

Most airports worldwide derive power from purchased electricity and fossil fuels to fulfill the considerable energy demands required for both land and airside operations. Fossil fuels are typically used in airports’ vehicles, boiler systems, and emergency generators, and electricity is utilized to supply airports’ buildings and infrastructure with the necessary lighting and air-conditioning loads [24]. Owing to the large 24-7 operations and services in buildings, electricity is always the dominant energy source in airports. Different climatic conditions dictate the level of energy usage within a building. For instance, countries with extreme cold or hot weather conditions would have higher energy consumption for heating, ventilation, and air conditioning (HVAC).

Airports are energy-intensive. The energy consumption of some busy airports may be compared to that of cities. Therefore, it is important from both energy and environmental perspectives (i.e., carbon footprint) that energy management is in place. Two key strategies help to enhance such management. One is through energy efficiency initiatives and the other through energy conservation.

Energy efficiency, in simple terms, is the use of less energy to perform the same task, whereas energy conservation is the effort to reduce energy consumption (hence avoiding wasted energy). The details of both strategies are discussed later in this paper.

1.5. UN Sustainable Development Goals and Aviation Sector

In addition to CORSIA’s initiative, there are other international organizations such as the United Nations through its Sustainable Development Goals (UNSDGs), which also aim to limit and reduce carbon emissions worldwide and across all sectors. With a universal call to act upon ending poverty, protect the planet, and ensure peace and prosperity for all mankind by 2030, the UN adopted the following SDGs (Figure 4).

In the wake of the COVID-19 pandemic, which hit the aviation sector hard, there is a renewed focus on some aspects of sustainability and SDGs as the sector begins to launch again. For instance, stakeholders at the IATA General Meeting in 2021 committed to striving towards net-zero carbon emissions by 2025, a goal that clearly aligns with SDGs 7 and 13 [26].

At first glance, it may appear that only goals 7 and 13 are relevant to addressing the aviation sector’s energy and sustainability challenges; however, there is more to consider. While there are certainly economic and societal benefits acknowledged by the sector, there are negative impacts on us and our environment. A few examples that align with the SDGs listed above include the following.

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Health aspects, where both air and noise pollution affect residents in the vicinity of airports and under flight paths. According to the World Health Organization, being subjected to continuous noise interference can cause cardiovascular and psychophysiological effects, sleep disturbance, reduced performance, provoke annoyance responses, and result in antisocial behavior [26]. Hence, from this perspective, SDG 3, which addresses good health and well-being, is undoubtedly concerned with the aviation sector and airport locations in particular.

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Land use by airports is also an important factor from the sustainability perspective. Utilization of land to build airports is commonly associated with detrimental effects on natural habitats and ecosystems, such as groundwater contamination and erosion of land [26]. SDG 15, which covers the significance of protecting ecosystems and reversing land degradation, is an important goal.

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The use of anti-icing to remove frost, snow, or ice from aircraft surfaces or runways can also have adverse environmental and human health impacts [26]. Here, SDGs 3 and 15 may be of concern.

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Indirect impacts caused by the use of SAFs could also affect sustainability through various means, both positively and negatively. Positive impacts could simply be the use of SAFs to reduce CO₂ emissions and hence pursuing SDGs 3, 7 and 13. However, this can also have negative impacts in terms of land use (hence SDG 15) when this involves securing feedstocks for SAF. Acquiring large areas of land to secure SAF production may also negatively affect food security (i.e., SDG 2) and cause imbalanced consumption and production of raw materials to secure SAFs (i.e., SDG 12).

2. Objectives

2.1. Aim

This study investigated the role of airports in the aviation sector from both energy and sustainability perspectives.

2.2. Research Gap

This study is distinguished by two primary objectives, as follows.

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To fill the knowledge gap concerning airports’ role in enhancing the aviation sector from the perspective of sustainable development. This includes all three pillars of sustainability (environmental, societal, and economic) with a focus on the energy aspect.

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To provide practical recommendations based on the results of both a literature review analysis and feedback from various international airport representatives and organizations.

2.3. Research Questions

The key research areas that this study sought to address are as follows.

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Present status of today’s airports worldwide from an energy and a sustainability perspective.

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Challenges and obstacles hindering the use or expansion of renewable energy within airports.

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Practical steps and policies required to promote sustainability within airports.

The above points should provide vital information for any serious future considerations and strategies to enhance the diffusion of greener airports.

3. Methodology and Case Study

The methodology used in this study involved both a literature review and responses to questionnaires targeting various airports and key aviation organizations, such as ICAO and IATA.

3.1. Literature Review Approach

The methodology used for collecting data involved an integrative literature review. Unlike other types of reviews, whether semi-systematic or systematic, integrative reviews usually have a different purpose and aim to assess, critique, and synthesize the topic in question, enabling new theoretical frameworks and perspectives to develop [27]. For mature topics, such as the aviation sector, the literature review method provides an overview of the knowledge base and expands the theoretical foundation of the topic as it develops [27].

3.1.1. Search Strategy

This study aimed to explore the present and potential role of airports in the aviation sector in terms of clean energy adoption and sustainability. The following key search string was used to identify relevant articles on the subject: aviation OR airports AND Energy OR renewable energy AND sustainability AND climate change OR carbon emissions.

The reason behind the choice of search string words was to allow greater coverage of articles covering the subject. For instance, using the terms aviation, energy, and sustainability served the purpose of generating as many hits related to the subject as possible, where further screening concluded the relevant papers to be discussed and investigated in the study. Figure 5 illustrates the methodological approach adopted in this study.

3.1.2. Search Database

The choice of the Scopus database for this study was not arbitrary. The database has earned its place as a comprehensive bibliographic data source and has proven to be reliable and in some respects even better than other databases such as the Web of Science (WoS) [28]. Founded by Elsevier in 2004, Scopus is a multidisciplinary and selective database that includes content from many specialized databases such as Embase, Geobase, and Biobase. A key advantage of the database is that all its contents are accessible with a single subscription without possible modulations [28]. Moreover, there are several other advantages behind the choice. The key advantages include:

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Better suited for evaluating the research results.

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Having a wider and more inclusive content coverage.

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Implemented impact indicators perform equally well and even better than the metrics of other databases such as WoS.

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Subscription to one single database with no additional restrictions regarding content accessibility.

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It is more open to society, as it provides free access to author and source information, including metrics [28].

All of these advantages were deemed helpful in serving the purpose of the literature review.

3.1.3. Search Parameters

To understand the significance of having a wide range of hits covered from the search with only relevant papers for analysis, the following parameters and limitations were set:

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Search within: All fields.

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Limited to: Review papers and English language.

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Year range: 2000 till 2023.

The following irrelevant topics were excluded.

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Computer science.

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Mathematics.

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Agricultural and biological sciences.

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Biochemistry, genetics and molecular biology.

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Immunology and microbiology.

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Pharmacology, toxicology and pharmaceutics.

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Psychology.

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Health professions.

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Neuroscience.

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Nursing, veterinary.

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Chemical engineering.

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Business, management and accounting.

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Chemistry.

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Materials science.

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Arts and humanities.

To reflect on the study’s research subject, it was necessary to identify the following set of information for the analysis.

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Geographical distribution of paper.

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Authors’ country.

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Type of renewables.

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Encountering challenges.

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Solutions suggested.

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Papers’ influence focus area.

Parameters such as encountering challenges, solutions suggested, and the paper’s influence focus area served to understand the key approach adopted in addressing the aviation’s environmental and sustainable development issues. Including the authors’ countries and the countries addressed in the paper served to identify any global trends. The types of renewables, if mentioned, helped indicate any favored sustainable energy used in the sector.

3.2. Questionnaire

Questions are commonly divided into two broad categories: closed-ended and open-ended. An open-ended questionnaire was used in this study. This gives the respondents the opportunity to reflect on their opinions in the best possible way, unlike closed-ended questions, which limit the use of respondents’ own words. However, it is worth noting that applying open-ended questions is more complex and requires in-depth analysis and grouping of varying responses [29].

Two questionnaires were used in this study. One targeted airports and the other focused on decision-makers and organizations within the aviation industry (for example, ICAO, IATA, etc.). Although a few questions were similar, they still intended to question the perspective of the type of participant involved in representing an airport or an organization.

Acknowledging the difficulty of receiving responses, it was crucial that the questionnaires reach as many participants as possible. The easiest and fastest means to send the questionnaire was through email. To facilitate and attract participants to respond, the following measures were applied:

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A cover email was included to explain the survey’s purpose, the participants involved, and the significance of the study.

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An introduction about the subject was enclosed prior to the questions.

Moreover, to ensure the unbiasedness of the questions, it was important that no leading questions were asked, and hence yes/no questions were avoided (questionnaire and responses are given in Supplementary Materials).

3.3. Respondents—Airports and Organizations

To receive as many responses as possible, it was important to send emails to a large number of potential respondents. This also served the purpose of seeking airports of various sizes in different environments and possibly continents worldwide. Out of the 15 airports approached across all continents and two organizations (ICAO and IATA), the following responded:

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Dubai International Airport.

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Muscat International Airport.

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Stockholm Arlanda Airport.

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Sydney Airport.

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Toronto Pearson International Airport.

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Zurich Airport.

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International Civil Aviation Organization (ICAO).

Table 1. Key figures on the size of the airports (respondents).

Airport	Built (Year)	Country, City	Airport Location	Passengers per Year	Cargo per Year (Tons)	Destinations	Terminals, Runways	Area (Acres)	Employees
Dubai Int. Airport	1960	UAE, Dubai	4.7 km east of Dubai city center	86,878,900	1,805,898	262	3 terminals, 2 runways	7200	7700
Muscat Int. Airport	1973	Oman, Muscat	32 km from Muscat old city	12,599,545	168,824	146	1 terminal, 2 runways	5500	2000
Stockholm Arlanda Airport	1959	Sweden, Stockholm	37 km north of Stockholm	21,800,000	96,710	154	4 terminals, 3 runways	2500	17,000
Sydney Airport	1920	Australia, Sydney	8 km south of Sydney’s central business district	38,650,000	320,170	90	3 terminals, 3 runways,	2241	30,000
Toronto Pearson Int. Airport	1937	Canada, Toronto	22.5 km northwest of downtown Toronto	44,800,000	428,468	195	2 terminals, 5 runways	4600	50,000
Zurich Airport	1948	Switzerland, Zurich	13 km north of central Zurich	28,885,506	377,998	205	3 terminals, 3 runways	1100	25,000

provides a few key figures reflecting the size and magnitude of the traffic involved in the airports that responded.

4. Results

4.1. Literature Review Approach

The initial search yielded 505 hits, and the final results revealed that 49 scientific papers were relevant for further categorization and analysis. The list of the included papers and the index of information are presented in Supplementary Materials.

4.1.1. Search Database

After reviewing the 49 papers, it became evident that nearly 80% of them focused on addressing sustainable aviation fuels (SAF) as the key means to help reduce the environmental impacts (namely CO₂ emissions) caused by the aviation sector. A large proportion of hits were on hydrogen and biofuels. The word cloud shown in Figure 6 and

Table 2. Keywords and their corresponding hits of the concluded 49 papers.

Word	Number of Hits
Biofuel	15
Hydrogen fuel	8
SAF	7
Alternative aviation fuel	4
Hybrid electric aircraft	2
* Aviation fuel, blends, electrofuel, etc.	1

* Terms with 1 hit: aviation fuel, blends, electrofuel, renewable energy, renewable grid, bio-renewable butyl butyrate, sustainable aviation, aircraft design, aircraft operations, aircraft engines, tourism aviation—climate change, environmental impact analysis, decarbonizing heavy duty transport.

reflects this unanimous representation of the papers’ covered subjects. Other papers addressed tackling the sector’s negative emissions through other means such as electrification of aircraft, use of additive composite materials, and enhancing policies related to tourism travel, climate change, and carbon emission limits.

Among the 49 papers (see Supplementary Materials), only three addressed the significance of adopting renewables within airports. This was found in only the papers titled: “Review of electrofuel feasibility—Prospects for road, ocean, and air transport,” “Decarbonising ships, planes and trucks: An analysis of suitable low-carbon fuels for the maritime, aviation and haulage sectors” and “Net-zero emissions energy systems.”

The review papers can be grouped into three subject areas: sustainable alternative fuels (including both hydrogen and biofuels), renewable energy infrastructure, and innovative solutions.

4.1.2. Challenges Encountered

Similar challenges were identified across the sustainable alternative fuel papers. The most recurring challenges included the following.

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Feasibility: The production pathways for either fuel remain a challenging factor, starting from the logistics and availability of the source (e.g., feedstock) to the conversion into fuels (e.g., boilers) and transportation, along with securing the storage means, all accounting for the feasibility of the fuel in question.

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Future Implementation: Changes in and development of aircraft engines (e.g., propulsion systems) to suit SAF [30].

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Economic burden: Huge enduring costs projected to help match alternative fuels to any newly designed engines. Costs are also attributed to the new infrastructure needed within airports for storage and transportation in the vicinity.

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Policies: Lack of continuous appropriate regulatory and incentive frameworks to support SAF and overcome barriers.

In terms of the challenges of renewable energy adoption within airports, those presented in the few identified papers typically covered:

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Flexible generation: Although renewables such as wind and solar are envisioned as important sources of electricity, their intermittent nature makes them problematic in the long run when supply and demand do not align [31].

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Highly reliable source of electricity: As mentioned earlier, the disadvantage of not having a continuous source of energy results in a requirement for investment in an energy storage facility [31].

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Policies and incentives: Similar to the SAF category, the necessity of supporting policies for adopting renewable energy as an electricity source, whether to be used for the airport or even as an e-fuel, is crucial [32].

4.1.3. Recommended Solutions

Common recommendations have been reported in the literature. Typical examples identified were:

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Continuing research and development to address emissions, whether through SAF or RE (electricity), is economically viable.

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Cooperation among stakeholders, aviation experts, governments, RE and SAF companies, and even agriculture organizations were seen as significant for the success of any initiative.

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Encouragement from governments, banks, and investors also stood out as key players in overcoming economic barriers [33].

4.1.4. Geographical Distribution

Most studies have addressed this subject on a global level. Few papers presented case studies that focused on their own countries. A paper titled “From farm to flight: cover cress as a low carbon intensity cash cover crop for sustainable aviation fuel production—A review of progress towards commercialization” covered the USA, whereas the paper “Analysing the opportunities and challenges for mitigating the climate impact of aviation: A narrative review” covered Sweden.

It was interesting to find that only five countries were discussed in 49 papers. These were Australia, Brazil, Singapore, Sweden, and the USA (See Figure 7). This may not be surprising, especially for Brazil and the USA, since these account for a large share of the total biofuel used in the world [34]. The pie chart below reflects the representation of the 49 papers by country.

The authors’ affiliation by country was another factor used to examine whether there was any pattern or trend across the globe. As seen in the figure below, the USA dominated the list. Other obvious author countries were the UK, China, and Brazil (Figure 8). A total of 36 countries were associated with the authors of these papers. This reflects a wide range of global interest in reducing aviation sector emissions.

4.2. Questionnaire

It is worth noting that not all responses provided direct answers to the posted questions (the details of all responses are provided in Supplementary Materials). Instead, they responded with either a website or a link to visit. This was encountered with Sydney, Toronto, and Zurich airports and the ICAO respondents. In the case of airports, key notes from the links provided were checked for relevance to the posted questions and inserted accordingly into Supplementary Materials for further analysis. However, since the questions for the ICAO concerned airports in general, it was best to provide a summary of the organization’s view and understanding of airports through a number of documents and review papers (See Supplementary Materials).

4.2.1. Challenges Encountered—Dubai, Muscat, and Sweden Airports

Interestingly, three responses were received regarding the barriers facing airports in terms of energy transition. While officials at Dubai Airport raised concerns about the airport’s infrastructure for incorporating SAF, Muscat Airport expressed three factors as the main barriers, namely the technology’s cost, lack of energy experts, and an eco-system enforcing body. On the other hand, Sweden Airport stressed the pressing need for a charging infrastructure (i.e., through renewables) within the airports.

4.2.2. Key Measures—Dubai, Muscat, and Sweden Airports

Dubai Airport listed several measures to be considered in addressing the aforementioned barriers. These included R&D continuation, collaboration among stakeholders, and enhancement of policies and incentives. Muscat and Sweden airports had similar measures. All three stressed the significance of cooperation among all stakeholders.

4.2.3. Challenges Encountered—Sydney, Toronto, and Zurich Airports

No clear answers were identified from the referred links for Sydney and Toronto airports; however, texts found for Zurich Airport clearly indicated the unavailability of renewable fuels and the unforeseen costs.

4.2.4. Key Measures—Sydney, Toronto, and Zurich Airports

Various measures were noted in the links provided. Sydney’s course of action focused on the securing of 100% RE through a contractual power purchase agreement (PPA) (a step that is believed to support the airport’s electricity source to a renewable one by 2025).

Both Toronto and Zurich airports indicated their practical measures in terms of electrification of their ground equipment and vehicles and switching conventional lighting to LED.

4.2.5. Summary—Questionnaire Responses

There is no doubt that all airports are aware of the negative environmental impacts created by the sector and are working towards addressing this issue. Direct responses from the Dubai, Muscat, and Sweden airports reflected the importance of airport infrastructure in tackling emissions. In fact, Dubai Airport explicitly stated the significance of such infrastructure for accommodating alternative fuels. Short- and long-term goals, along with perceived setbacks, were clearly identified among all three respondents.

4.3. Literature Review and Questionnaire Responses

Results from the literature review revealed that the focus of addressing the sector’s negative environmental impacts was primarily on the adoption of alternative fuels (an area that we were not anticipating to discuss in great depth). Responses from airports (i.e., Dubai, Muscat, and Sweden) focused on airport infrastructure. Both the included papers and responses indicate the significance of collaboration among various stakeholders.

5. Discussion

It is indicative from the results (literature review and responses) that airport and aviation decision-makers are concerned about the sector’s negative environmental impacts and sustainability. In response to these concerns, several initiatives and actions have been undertaken. There are certainly key global initiatives such as CORSIA, where there is a unified front among states to confront the sector’s emissions, and there are also independent efforts. It is worth acknowledging that different states have different capacities for addressing carbon emissions and sustainability. Capacity limitations may be attributed to a lack of knowledge, technology, R&D facilities, financial support, or access to key equipment involved in monitoring or control. Poor management/decision-making or even a lack of interest in addressing the subject may also act as a barrier and hence limit any efforts.

The literature review results indicated that most papers covered the adoption of sustainable aviation fuels. This information leaves no doubt about the sector’s inclination towards this key strategy to reduce carbon emissions. This may be attributed to the influence of global initiatives, such as CORSIA. Moreover, the interests of leading aviation countries in SAF, such as the USA, may have also played a dominant role in both scientific research and actual implementation. The literature review results clearly paid little attention to airports’ role in enhancing the sector’s combat against rising carbon emissions.

Given the study’s limited time and resources, it was difficult to verify the magnitude of airport initiatives in reducing carbon emissions. However, with the airport respondents, it was possible to visualize how far airports had gone to become greener and support the sector altogether. For instance, Oman Airports has started introducing clean energy alternatives. This included the installation of LEDs in its facilities’ light fixtures, street lights, and solar panels to reduce its carbon footprint [35]. Swedish Airports and its airport operators Swedavia have progressed well in addressing the energy of its facilities. For instance, all energy used to heat and cool the airports, providing lighting and running equipment, comes from renewable energy sources such as wind and hydropower. Moreover, Swedavia purchased green district heating produced from biofuels, including wood chips and other forest by-products. Swedavia vehicles currently run on fossil-free gas, HVO, and green electricity. Further south from Sweden, Dubai International Airport has also achieved success by installing 15,000 photovoltaic panels at Terminal 2 to generate 7,483,500 kWh of energy annually. According to airport officials, this is expected to reduce the terminal load by 29% and reduce the airport’s annual CO₂ emissions by 3243 metric tons [36].

Other respondents, such as Zurich, Toronto Pearson, and Sydney airports, had similar sets of actions to address their carbon footprint and sustainability. With the goal of setting a net-zero target for its own emissions by 2040, Zurich Airport took key measures along with its support for SAF. These included renovating airport buildings with new energy systems, such as photovoltaics, and investing in e-mobility across all its airport’s vehicles [37]. Similarly, Toronto Pearson Airport in Canada aimed to address its greenhouse gas emissions through energy reduction initiatives. The key ones to mention include upgrading its Terminal 1 facilities with light-emitting diode (LED) lighting and optimizing air-quality sensors to help achieve better monitor/control of temperatures and avoid any energy losses through overheating or cooling [38]. Sydney Airport, on the other hand, found that it has come a long way towards achieving its carbon neutral certification for the year 2025. The key initiatives adopted included a power purchase agreement (PPA) for 100% renewable electricity, implementing an energy efficiency program, and developing a carbon offset procurement strategy [39].

The results of this study reflect two main pathways for addressing the sector’s emissions: the adoption of SAF and its associates (drop in, etc.) and dealing with airports’ infrastructures, making these more energy-efficient and environmentally friendly. Regardless of the pathway chosen or prioritized, it is vital to understand that neither of these paths would be effective unless a holistic sustainability perspective is present.

Despite the potential of SAFs and the progress made in decarbonizing the aviation sector, the uptake of such fuels remains low (covering only 250,000 flights in 2020) [40]. This is attributed to sustainability aspects, namely the technoeconomic, social, and environmental aspects. The ability to successfully commercialize SAF requires comprehensive representation and agreement among the various stakeholders involved. Although this may seem like an “easy implementation,” it is quite challenging. A literature study pointed out some key challenges preventing SAF’s anticipated uptake, such as lack of availability, limited production facilities, technical uncertainty, the general public’s perception, the environmental impact of production and distribution, policy uncertainty, and economic considerations [40].

Whether it is SAF or a focus on having greener infrastructure for airports, it is necessary to identify the stakeholders involved. The definition of stakeholders according to Freeman and Reed is “those groups without whose support the organization would cease to exist” [41]. With such a definition in place, taking the SAF supply chain as an example would then at the least involve the following players: state/government representatives (e.g., ministries, regulators), industries (for example, SAF producers, distributors, aviation fuel handling companies, airport operations, airlines), nongovernmental organizations (NGOs; this could be anything from research, academic organizations, to energy consultants, environmental organizations, etc.) [40]. Moreover, within these key stakeholders, which are inevitably interdependent, the pillars of sustainability (i.e., economic, environmental, and societal) need to be considered and addressed. A straightforward economic viewpoint might challenge SAF’s comparatively high costs. In an analysis of sustainable aviation fuel stakeholders, interviews revealed a consensus among airlines that the price of SAF is high and a reduced-price gap with fossil fuel is required [40]. The societal impact of an increase in airline tickets owing to SAF adoption is another crucial issue to consider. The environmental aspect is also a challenge with indirect land-use changes to secure the required feedstock.

Behavioral change is another societal tool that may be utilized to help both SAF and airports address carbon emissions. Findings from an American study aimed at determining the impact of routes and tourism on the sector revealed that direct flights generally outperformed connecting ones regarding carbon emissions [42]. This study is based on the carbon budgeting approach of the German Advisory Council on Global Change, which suggests that keeping global warming below 2 °C, a threshold identified by scientists as dangerous and irreversible, requires that each human not exceed an average annual carbon budget of 2300 kg CO₂, of which one-fourth is allotted to transportation (i.e., 575 kg CO₂). Comparing direct and indirect routes, it was found that most direct flights exceeded 575 CO₂ kg/p.

With this set of information, the study concluded that possible means of reducing carbon emissions associated with tourist air travel would be simply not to fly to tourist destinations, because these comprise 20% of the US’s air travel emissions. The study added that if travel is necessary, non-stop routes would have a lower carbon footprint [42]. In this case, the societal aspect is indicative and has a direct impact.

With regard to the present study, results from both the literature review and the responses showed that there was no magic wand and no single solution to this “wicked” problem. With collective efforts from all stakeholders (airports, states, airlines, etc.), understanding one’s own capacity, and taking sustainability into account, only progress and success can be achieved. Furthermore, parties should acknowledge that addressing aviation emissions would require working on several fronts simultaneously and that there are various milestones to be achieved. While upgrading airports’ infrastructure can certainly be a short-term goal to achieve, the adoption of SAF on the other hand requires more work and time to become commercialized and hence can be seen as a mid- to long-term objective. Moreover, it is worth noting that states that provide funding for airports have different goals and capacities to accommodate such objectives.

Today, airports are more than ready to work on improving their day-to-day carbon footprint. This short-term goal is certainly achievable, especially when looking at other success stories worldwide. As discussed earlier, Sweden’s Airports provides a good example and a role model. Practical solutions such as the adoption of renewable energy sources to feed airport terminals and associated buildings (e.g., parking and hotels) and replacing ground handling equipment (GHE) with electric modes are no longer far-fetched ideas or practices. Figure 9a shows a Scandinavian airline (SAS) officer at Stockholm Arlanda Airport connecting a ground-handling vehicle to charge. Figure 9b displays a typical amount of ground-handling equipment used in day-to-day operations at airports.

Renewable energy sources (RESs) serve sustainable airports with a wide range of energy services, starting from electricity, heating, cooling, and providing power to ground handling equipment and vehicles. There are many drivers for airports to adopt RESs. The obvious reason is the overall production of fewer emissions. RESs may also require less space and have a minimal impact on airport operations compared to large-scale power plants. Solar panels on rooftops may be a good example of such space efficiency. Volatility in fossil fuel prices and production is also a key driver that attracts governments and companies to invest in RESs at significant facilities, such as airports. In addition to helping stakeholders minimize their financial risks from utilizing fossil fuels, the average costs of two major RESs, wind and solar power, have continued to fall in recent years [43]. It was reported that an installed solar PV plant (12 MWp) at Cochin Airport, India, operating at nearly 87%, could mitigate 12,134.26 tons of CO₂ and had a payback period of 5.6 years (i.e., length of time to recover the cost of an investment) [24].

Energy management through energy efficiency measures and conservation is slowly becoming popular in airports. Common energy savings used today include the installation of energy-efficient electric motors in baggage building areas, upgrading to energy-efficient chillers, modernizing existing lifts, and improving the heating and cooling systems of terminal buildings. Other measures may include the installation of energy-efficient LED lights and replacement of diesel-powered auxiliary power unit (APUs) with electricity-powered APUs, which helps not only in increasing energy efficiency but also in reducing noise emission [24].

In addition to adoption of the technological means, it is similarly important that airports should be backed up by a set of enhancing policies and regulations to enable green transitioning. This was also expressed by the respondents as being one of the key measures for tackling barriers to realizing greener airports. The IATA’s recent policy analysis focusing on supporting RESs within the sector provided the following conclusions:

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The importance of creating energy policy frameworks is tailored to local conditions and is supported by international cooperation.

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Strategic policy sequencing has a positive impact on the creation of a new energy market, with technology-push policies and demand-pull measures.

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The importance of early and substantial governmental R&D support is a crucial element in fostering competition and diverse solutions, with market-based policies implemented as technologies mature.

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It is necessary for all supply chain stakeholders to be subjected to predictable, long-term, and globally harmonized policies.

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There is an urgent and substantial practical and financial need to support emerging economies in the development of new energy markets [44].

The analysis also provides examples of effective and practical policies that could align with the sector’s decarbonization goals. Several key topics include the following.

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Feed-in Tariff (FIT): A policy that guarantees a fixed price for electricity over a specified timeframe, thus ensuring stable predictable revenue for RES producers and airports. This policy, as described by IATA, reduces risk, fosters investment, and spurs innovation in the sector.

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Power Purchase Agreement (PPA): A long-term contractual fixed-price policy often spanning 10 to 15 years helps mitigate fluctuating prices in the electricity market. Moreover, the policy agreement can sustain RES operations after expiry of government subsidies [44].

In ICAO’s guidance report titled “Practical applications to achieve carbon reductions and cost savings,” it was highlighted that different states and airports face different challenges and opportunities. Depending on available resources, allocated budgets, and existing policies, airports should seek opportunities within the given circumstances and environment. The adoption of RESs could be an example of this. While solar power could be a great option to pursue throughout the year in regions such as north Africa and the Middle East, it should certainly not be the favored option in countries with less sunshine, such as Iceland or Ireland. In summary, airports should try to make the best of their given capacities and environments and look for solutions in other success stories that share similar circumstances [45].

The Airports Council International (ACI) through the Airport Carbon Accreditation Program—championed by Muscat and Dubai airports—provides a robust framework for airports to transform their green goals into reality. For the past 15 years, the Airport Carbon Accreditation Program has equipped airports with a solid framework for managing carbon emissions, turning commitments into tangible achievements through clear and actionable steps. The program is seen to be successful because it transforms commitments into tangible results, providing airports with clear and effective strategies to lower their emissions. For instance, airports progress through four increasingly rigorous levels of accreditation—mapping, reduction, optimization, and transformation. For those reaching levels 3 and 4, there is an extra mile to go: offset their remaining emissions and they will earn ratings of 3+ (neutrality) or 4+ (transition) [46].

In addition to the study’s findings, it is also important to explore how other factors, such as airports’ traffic management, can influence the sector’s carbon emissions and airport sustainability. Air traffic management (ATM) is a term used to indicate all systems and tasks associated with the different phases of a flight, starting from departure to the journey itself and finally to the landing phase. Typically, an ATM comprises three key services: air traffic services (ATSs), air traffic flow management (ATFM), and airspace management (ASM), all of which are connected to air traffic control (ATC).

While ATSs are concerned with providing the aircraft’s crew with the required information throughout the entire flight, ASM controls the allocation of airspace to different users (e.g., civilian and military), while ATFM regulates air traffic flows to avoid airspace congestion [47].

A good example of adopting the ATM strategy is the European Green Deal initiative, which aims to tackle various sectors to achieve the continent’s climate neutrality by 2050. Under such initiatives led by the European Commission, several aviation projects are seeking better means of ATM. An example of such a project is the Green-GEAR project, which aims to develop innovative ATM procedures to enable and incentivize the use of optimum green routes and efficient airspace usage through the new Single European Sky ATM Research (SESAR) initiative [48].

Tobias Bauer, a researcher at the German Aerospace Center, explains the reason behind such a project. He stated: “Solutions such as sustainable aviation fuels and hydrogen or battery-powered electric aircraft are in the early stages of development, and their full roll-out will take decades.” He added: “Knowing an aircraft’s precise altitude could help pilots and air traffic controllers plan more efficient approaches, descents and climbs—all of which would reduce emissions, not to mention noise, in the airport vicinity.”

ATM strategies have recently been initiated and adopted (for example, the European Green Deal in 2019), but there are no measurable effects to analyze or study; however, the ambition is to reduce average CO2 emissions per flight by 0.8 to 1.6 tons by 2035 [49].

Key aviation organizations such as the ICAO also envision the significance of ATM in achieving a sustainable and efficient aviation system over the short to medium term. The ICAO identifies two key advantages in this context. The first is a reduction in fuel consumption and flight costs, while the second relates to operational measures that do not require the introduction of new equipment or implementation of costly technologies [50].

6. Limitations

The results of the questionnaire and literature review revealed the study’s limitations and potentially indicated areas for improvement. With additional time and resources, the following steps could enhance and expand on the current study:

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Introduce more search engines in the literature review (e.g., Google scholar, etc.).

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Acquire more responses from airports and certainly from other aviation experts, including airlines.

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Introduce new in-depth questions and tweak existing ones in the questionnaire to represent the aviation sector as a whole and not just airports. This may have resulted in different responses from the respondents.

7. Conclusions

The findings from the literature review and feedback collected suggest that the aviation sector acknowledges its harmful impacts on a global scale due to its contribution to greenhouse gas emissions. From these results, it appears that the success of reducing the sector’s emissions lies on two parallel fronts. One is the adoption of 100% alternative fuels (SAFs) and the other is through the transition of airports’ infrastructure. Adoption of 100% SAF in aircraft is still in its early stages of development and can be considered a long-term goal because it requires heavy engineering intervention and alteration of aircraft engines. Moreover, securing the fuels and the success of producing these fuels in a sustainable manner are still key barriers in the commercialization process. In addition, there is a requirement for airport infrastructure to accommodate such fuels safely and securely. Despite being used for a number of years, SAF “drop in” jet fuels are still costlier than traditional jet fuels, and their production levels are still severely limited.

On the other hand, the transition of airports’ infrastructure can be visualized as feasible and attainable, and hence should be considered a short-term goal. Many airports, including the respondents, have already worked on their infrastructure; however, they have also expressed concerns about the lack of enabling policies and incentives. Other measures, such as close collaborations among stakeholders, enhancing research and development, and government support, were also seen as significant for establishing greener airports.

The literature results indicate a clear preference in the papers for SAF solutions over the development of more environmentally friendly airports. This may indicate a major research gap in a significant integral part of the aviation sector. It is therefore important that member states collaborate and work closely with key organizations such as the ICAO, IATA, and the UN through its SDGs in order to breach this research gap and be able to establish more sustainable airports within a shorter period of time.

8. Future Prospects

There is no doubt that green technologies will contribute to environmentally friendly airports; however, this would also introduce different operational procedures and control regulations from the traditional methods [17]. Stakeholders need to be aware of the challenges this change presents and collaborate to overcome it. Being active participants through key initiatives, such as CORSIA and Airports Council International (ACI), and learning from other success stories will inevitably have a significant positive impact on achieving set goals. There is no doubt that greener airports are growing in number; however, a faster pace is needed to meet the steady rapid growth of the sector.

Perhaps shifting the focus from SAF-only solutions towards short-term goals (i.e., investment in greener airports as well as improving present ATM strategies) may have a more positive, effective, and quick impact in reducing the sector’s emissions.