Sustainability in Aviation: A Mission Impossible?

9 May 2024 | Blog #4

The topic of sustainability has now permeated all areas of daily life. From our consumption habits to the economy and environmental preservation, the idea of sustainability increasingly shapes our decisions and actions. In a time where the impacts of climate change are becoming more tangible and environmental issues are gaining global significance, it is more crucial than ever to understand and implement the principles of sustainability into practice. This development not only reflects a growing awareness but also marks an important step towards a responsible and sustainable society. 

The aviation industry is often scrutinized by the media and branded as a major environmental polluter, particularly regarding CO2 emissions. This portrayal casts a negative light on the industry, implicating it significantly for the impacts of climate change. However, a closer look at the numbers reveals a different picture within the transportation sector. The global CO2 emissions from mobility are primarily caused by road transportation, accounting for a staggering 72%. Aviation follows at a distant 12%, followed by maritime transportation at 10%, and rail and other modes at 6%. According to the International Air Transport Association (IATA), aviation contributed approximately 2.7% to global greenhouse gas emissions in 2019 (the highest year in the history of commercial aviation), with only 0.52% within Europe and as low as 0.16% in Austria. These greenhouse gas emissions are the basis for transporting around 4.5 billion passengers (in 2019) over approximately 8,700 billion passenger kilometers, using about 33,000 commercial aircraft operated by approximately 1,500 airlines serving around 3,800 commercial airports. Consequently, a flight passenger covered an average distance of 1,930 km per flight. When applied to the most modern aircraft types such as the Boeing 787, Airbus 220, or Embraer E2 190, this results in a kerosene consumption of 3 liters per passenger per 100 kilometers flown. However, it is expected that this share will further increase in the coming years due to the almost continuous growth of air traffic. Therefore, IATA has set a goal to reduce net greenhouse gas emissions by 50% by 2050 compared to 2005. Greenhouse gases, according to the Kyoto Protocol of the United Nations Framework Convention on Climate Change of 1997, include not only the most prominent member, CO2 (carbon dioxide), but also nitrous oxide (N2O), methane (CH4), and fluorinated gases (F-gases) such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) 

No matter which perspective one considers this issue from, aviation emits greenhouse gases on a large scale and is inherently compelled to take measures to reduce, or if possible, halt its contribution to climate change. But how can this be achieved in concrete terms? 

First and foremost, it is necessary to take a closer look at three essential concepts in this context and familiarize oneself with them. At the core of this discussion lies climate change. The term "climate change" refers to alterations in the long-term average weather conditions on Earth. It involves not only short-term fluctuations but also long-term trends, particularly concerning temperature, precipitation, wind patterns, and other climatic elements. Climate change is widely believed to be largely influenced by human activities, primarily through the release of greenhouse gases such as carbon dioxide (CO2) into the atmosphere, mainly from the combustion of fossil fuels. Skeptics of anthropogenic (human-caused) climate change present various arguments to question the underlying theory, including natural climate variability and cyclical climate patterns. 

Building upon this, it is essential to scrutinize the concept of "sustainability" more closely. Originally stemming from forestry, the term "sustainability" means that a forest is sustainably utilized when only as much wood is harvested as regrows. This principle has been extended to other areas such as economics and society. Sustainable development, in this sense, means development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It aims to create lasting fulfillment of needs by preserving the regenerative capacity of the systems involved. Sustainability is thus based on three pillars: ecology, economy, and social aspects. To be deemed "sustainable," aspects of all three pillars must be fulfilled. 

In the context of sustainability and transportation, the term "carbon neutrality" often arises. Therefore, it is important to establish the conceptual definition of "carbon neutrality". What does it actually mean to be carbon-neutral or to operate in a carbon-neutral manner? Essentially, it involves reducing the amount of greenhouse gases caused by human activities and offsetting the remaining emissions through appropriate measures. Carbon neutrality requires minimizing one's own carbon footprint, whether through energy conservation, sustainable mobility, or the use of renewable energy sources. Companies and organizations are increasingly integrating environmentally friendly technologies to make their production and services more climate-friendly. A key approach to carbon neutrality lies in offsetting unavoidable emissions. This is often done through investments in projects to reduce greenhouse gases elsewhere. Despite all efforts, the question arises: Is complete carbon neutrality even possible? Some skeptics argue that it is nearly impossible to eliminate all emissions. Nevertheless, the pursuit of carbon neutrality remains a significant step towards environmental protection and sustainability. While achieving complete carbon neutrality may pose a challenge, the measures and compensation mechanisms implemented allow for a significant reduction in the ecological footprint. In the exploration of the concept of carbon neutrality, it becomes clear that it is not only about abstaining but also about innovation and the use of new technologies. The search for carbon-neutral solutions opens up opportunities for sustainable development and encourages a rethink regarding our impact on the environment. Thus, the vision of carbon neutrality remains not only a goal but also a driving force for a more conscious and responsible management of our planet's resources. 

The aviation industry now faces these three challenges in this context in the long term. But before possible solutions are discussed, attention should be paid to the rapid development of commercial aviation. Over a period of 50 years (1969 to 2019), aircraft propulsion efficiency has increased by 80%. Furthermore, it is worth noting that over a 30-year period from 1989 to 2019, the production of commercial aviation (expressed in RPK - Revenue Passenger Kilometer) has increased fourfold, while emissions have only doubled. These figures illustrate the rapid development of this mode of transport alongside technological innovations. 

Aviation, through the consumption of kerosene, is undeniably responsible for three major impacts: the emission of carbon dioxide (CO2), nitrogen oxides (NOX), and contrails. The emission of CO2 by aviation was estimated for the year 2023 at approximately 70 million flight hours (worldwide), which translates to a carbon dioxide emission of around 700 million tons. The fundamental issue with carbon dioxide is its "durability," as CO2 remains in the atmosphere for several decades. Therefore, the cumulative approach has a drastic effect: when added up over the years, this leads to massive impacts on global warming. NOX, as a greenhouse gas, has greater effects on life on Earth than CO2. Compared to CO2 (carbon dioxide), NOX gases have a shorter atmospheric lifetime, but they are more potent greenhouse gases in many respects. Aspects such as greater heat retention, influence on the ozone layer, and participation in atmospheric reactions are significant reasons why NOX gases are considered significant climate drivers. NOX gases undergo faster atmospheric reaction and distribution than CO2. While CO2 remains in the atmosphere for long periods, NOX gases can have quicker and localized impacts. Finally, contrails take center stage. The typical cruising altitude is 10 km above ground where temperatures are -40 degrees Celsius or colder. According to the German Aerospace Center (DLR), this cold air cannot absorb the water vapor from aircraft engines as well as warmer air. What happens then is akin to a sponge saturated with water unable to absorb any more liquid: water droplets form, creating artificial clouds (contrails). These contrails often persist for several hours, are blown by the wind, and thus form additional artificial clouds (cirrus clouds). It seems clear that contrails contribute to warming the climate, possibly even as much as the CO2 emitted by aircraft. This is because contrails, acting like large veils of mist, may prevent sunlight and heat from escaping the Earth back into space. Consequently, they would intensify the so-called greenhouse effect, which heats our climate. Or do contrails possibly have the opposite effect? Does the bright surface of the clouds reflect sunlight so strongly that some of it is radiated back into space? If so, contrails would counteract the warming of our planet. In other words, do the clouds act like the glass roof of a greenhouse or like a mirror? It is currently assumed that contrails have a temporary impact lasting 10 to 15 hours. 

Despite partially well-developed alternative modes of transportation, the airplane remains indispensable when it comes to quickly, comfortably, and affordably covering both long and short distances. This is particularly evident in Europe, given its geography and topography. It is little known that 25% (134) of all European airports (excluding Russia and Turkey) are located on islands. In this regard, alternative modes of transportation such as waterways are the only alternative, which are often associated with significantly longer travel times, fewer connections, and greater exposure to weather conditions, leading to flight cancellations. In this context, aviation is an irreplaceable institution for islands, supporting the local population in numerous aspects: connectivity with the "rest of the world," supply of urgent goods (especially medicines), facilitation of ethnic traffic (VFR - Visiting Friends and Relatives), and promotion of tourism. 

It is clear that aviation continues to be essential in relation to feeder functions to air transport hubs. Despite the efforts of the EU to require direct rail connections (thus enabling intermodality on a larger scale) from all airports with an annual passenger throughput of over six million, this endeavor is still far from its goal. Currently, only 47 airports (62%) can meet this requirement, with only 77 airports (14%) across Europe having a direct rail connection. This low number is partly due to the island factor already described, and countries such as Iceland or Malta have no rail infrastructure whatsoever. In general, it can be said that rail transportation cannot replace flights. This conclusion is reached by a study regarding the cessation of flights between Salzburg and Vienna and can be used as a starting point for evaluating other regional flight routes as well. Various options and associated offers should be maintained for different target groups. A ban or cessation of feeder flights does not lead to effective CO2 reduction, as CO2 emissions are capped under the EU Emissions Trading System throughout the EU. Any additional national savings allow for additional CO2 emissions elsewhere in the EU. This results in a neutralizing effect of the savings. Moreover, a shift in traffic to another hub may even lead to more emissions and ecological benefits may be lost. Contrary to expectations or claims, the railway is not inherently a beneficiary of the cessation or prohibition of regional or short-haul flights, depending on the specific target group. 

Aside from the potential CO2 savings in regional air travel or short-haul flights, the airplane is unquestionably the preferred and most effective mode of transportation for long-haul flights. Continuous advancements in aircraft development and manufacturing enable distances of over 15,000 km to be covered nonstop (without layovers). This allows airlines and airports with their networks to potentially reach large parts of the world population directly with flights, depending on the location of the departure airport. This segment (long-haul) faces constantly increasing demand. To save CO2, it is therefore necessary to increase distances with zero or negative CO2 emissions. This is primarily possible through new propulsion models that are on the verge of practical implementation. 

Among the alternative fuels are biofuels, which are currently used as a blend with conventional kerosene. They are made from vegetable oils, animal fats, or other organic waste. However, there are efforts to use biofuels as the sole fuel for aircraft in the future. Biofuels are already available and are available in larger quantities at airports in Europe such as London Heathrow and Amsterdam. 

Synthetic fuels are derived from hydrocarbons that can be obtained from renewable energy sources. They are also referred to as Power-to-Liquid (PtL) or E-fuels and can be used in existing engines. At the current time, there are no airports in Europe offering such fuels. 

Hydrogen is considered a promising fuel for aircraft because it only produces water vapor and no CO2 emissions when burned. However, there are currently technological challenges in implementation, particularly in production, storage, and end-use. In the case of aircraft, challenges arise regarding the storage and handling of hydrogen on board. 

SAF (Sustainable Aviation Fuel) is an umbrella term for various alternative aviation fuels (biofuels, synthetic fuels, and hydrogen) produced from sustainable sources and intended as alternatives to conventional kerosene. Availability of SAF is already partially established worldwide, with particular emphasis on larger airports to quickly integrate it into the airlines' portfolios for blending (in combination with conventional kerosene). The European Union (EU) plans to introduce a special environmental label in 2025 that will indicate the carbon dioxide footprint per passenger for air travel. The aim is to simplify the comparability of different airlines. The EU aims to curb the proliferation of eco-claims and create transparent comparability among airlines with the planned environmental label. In the future, blending of SAF (where technically feasible) will also become mandatory according to EU regulations. From 2025, a 2% blending is mandated. Subsequently, the mandatory SAF blending rates will be incrementally increased. By 2030, the quota will be raised to 6%, then to 20% by 2035, 34% by 2040, 42% by 2045, and by 2050, it is projected to reach 70%. 

Lastly, the topic of electricity as another propulsion model warrants further examination. Electric propulsion for aircraft is still in development. However, there are already smaller aircraft that can be flown exclusively with electric propulsion. Electric aircraft in commercial aviation are expected to start in regional air travel, as smaller aircraft are used here. The first commercial flights can be expected no earlier than 2025. 

Regarding the previously mentioned range with alternative fuel models, this will gradually increase over time. Electric propulsion will initially allow for a distance of up to 900 km. The use of hydrogen then increases the distance to 1,400 km, expected around 2028. Further significant advancements are possible subsequently through the use of liquid hydrogen starting from 2035 (2,800 km). 

In addition to the aforementioned alternative propulsion models, airlines, airports, and other stakeholders are implementing further measures to reduce greenhouse gas emissions. These include: 1) emissions-based charges at airports for aircraft, 2) emissions trading: as an instrument to combat climate change (since 2012 for airlines), and 3) flight route optimization (under the Single European Sky initiative). 

Alongside airlines, airports also bear responsibility for the aspect of "sustainability in aviation," and many are taking tangible steps in this regard. European airports are actively working on implementing sustainable operational models to minimize their environmental impact. Some of the measures taken by airports include the following. In the period 2020/2021, there were 51 carbon-neutral airports in Europe, 10 more than in 2019. The carbon footprint of air traffic itself is not included in the airports' carbon balance sheets. The Airport Carbon Accreditation program by Airports Council International (ACI) Europe aims to have 100 carbon-neutral airports by 2030. Some European airports have set targets to become emissions-free or at least carbon-neutral by a certain timeframe. Many airports are utilizing renewable energies such as solar and wind power to meet their energy needs and reduce CO2 emissions. This includes transitioning ground vehicles from combustion engines to batteries. Airports are also implementing energy efficiency measures such as LED lighting to reduce energy consumption. They are working to make their infrastructure more sustainable by introducing rainwater-collecting roofs and green roofs to minimize ground sealing. Many airports have adopted sustainable construction principles to reduce the energy consumption and ecological footprint of their buildings. 

On a global scale, the CORSIA initiative is particularly significant for reducing greenhouse gases in aviation. CORSIA represents a cooperative approach moving away from a "patchwork" of national or regional regulatory initiatives. It provides a harmonized path for reducing emissions from international aviation, minimizing market distortions while respecting the specific circumstances and capabilities of ICAO member states. CORSIA complements other elements of the action plan by offsetting the amount of CO2 emissions that cannot be reduced through technological improvements, operational enhancements, and sustainable aviation fuels with emission allowances from the carbon market. 

Ultimately, there's the question of how individual air passengers can contribute to traveling sustainably by air. Concrete measures include simple things to consider primarily before the flight, as during the flight, there's little one can do to contribute. 

Traveling with as little luggage as possible is important, as the total weight of the aircraft directly affects fuel consumption. It's worth questioning how much clothing and accessories one really needs at the destination. This is best done by reflecting on past trips and realizing that one often travels with too much or unnecessary luggage. Choose eco-friendly and buy from sustainable luggage brands that use recycled materials. Use a smartphone to download the boarding pass, limiting additional paper consumption, as well as the ink used daily to print millions of boarding passes. As for travel literature, please don't bring paper books and magazines on the trip. In the age of e-books and online magazines, significant weight can be saved on flights, thus reducing greenhouse gas emissions. As for getting to the departure airport, it's recommended to use public transportation, preferably by train if a direct connection is available. The same applies, of course, to the destination airport and for the return journey. 

Research shows that airplanes consume the most fuel and produce the most harmful emissions during takeoff. For example, during a short-haul flight, the takeoff can consume up to 25% of the aircraft's total fuel supply for a flight. Choosing direct flights instead of connecting flights (if possible) helps to limit greenhouse gas emissions. In more than 99% of cases, a layover results in longer flight distances overall. 

Another way to fly more environmentally friendly is to reduce flight emissions through offsetting. However, these offsetting schemes are criticized from various perspectives and should not be instrumentalized as "greenwashing" for sustainable aviation. There is a risk of the so-called "rebound effect," where individuals who offset their emissions may feel less incentive to reduce their own energy consumption. This could lead to people continuing environmentally harmful behaviors, believing that their emissions can be offset through compensation. Furthermore, there are uncertainties about how effective offsetting projects actually are. Some projects may not achieve the expected CO2 savings, and there are discussions about the accuracy of measurements and calculations. 

In summary, a new perspective on "sustainability in aviation" emerges with the following key pillars: 

• Resource Efficiency and Circular Economy: Sustainable aviation aims to use resources more efficiently and optimize the lifecycle of aircraft. This may include the development of lighter materials, more efficient engines, and innovative manufacturing technologies to minimize energy consumption and environmental impacts during the production, use, and disposal of aircraft. 
•  Social Responsibility: Sustainability in aviation also encompasses social aspects, including fair working conditions for aviation employees and consideration of community interests in airport developments. 
• Biofuels and Alternative Propulsion: Sustainable aviation explores alternative fuels such as biofuels, synthetic fuels, hydrogen, and electric propulsion to reduce dependence on fossil fuels and further reduce greenhouse gas emissions. 
• Optimization of Air Traffic Management: Efficient air traffic management helps minimize fuel consumption and make air travel more environmentally friendly. This includes the development of smarter flight routes, modern navigation technologies, and the use of advanced aircraft systems. 
• Research and Innovation: The aviation industry invests in research and innovation to develop innovative technologies and concepts that can further reduce environmental impacts. This includes new aircraft designs, more efficient propulsion systems, and advanced materials. 
• • Collaboration and International Standards: Sustainable aviation requires cooperation on a global scale. The development and implementation of international standards and agreements play a crucial role in ensuring that sustainable practices are applied worldwide in the aviation industry. 
• Holding Airports and Airlines Accountable: CO2 emissions also occur on the ground for aircraft handling and processes at airports on a large scale. The goal of greenhouse gas minimization requires coordinated collaboration between airlines and airports and setting long-term or ambitious goals. 
• As a Passenger: There are several things passengers can do to travel as sustainably as possible by airplane. 

Based on the aspects mentioned, it can therefore be deduced that despite all its past and present efforts, aviation cannot currently be classified as sustainable. The environmental impact of aviation today is greater than yesterday, and tomorrow it will be even greater than today. Therefore, current concrete measures, as they have already been implemented and will be implemented more intensively in the future, are indispensable to address the explosion in air transport in the aviation industry on all levels of environmental protection as effectively as possible.

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