35 Must Know Terms in Sustainable Aviation

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Note that definitions and interpretations of these terms may vary in different contexts and sources.

Welcome to the world of sustainable aviation – a sector that's transforming the way we travel and interact with our environment.

We're entering a new era where sustainable aviation is imperative to combat climate change and preserve the planet's resources. This involves leveraging technologies and practices that reduce fuel consumption, decrease greenhouse gas emissions, and minimise noise pollution from aircraft operations. That's why we have created a dictionary to help you understand the complex terminology associated with this rapidly evolving discipline.

Our objective with this dictionary is to simplify these intricate terms and concepts, providing clarity and making them accessible to a broad audience.

Sustainable aviation isn't exclusive to aviation professionals or environmental experts. It's an ongoing transformation that is significantly impacting our environment, economies, and global connectivity.

So, our hope is that this dictionary can serve you more than a reference tool. It aims to foster informed discussions by making complex ideas more digestible. It helps to bridge the knowledge gap and enables everyone to partake in this crucial dialogue, regardless of their background or expertise.

Whether you're a seasoned industry professional, a sustainability advocate, or simply interested in understanding the ongoing changes in the aviation sector, this dictionary is for you.

PARIS AGREEMENT

Adopted in 2015, The Paris Agreement is the first universal, legally binding global climate agreement with a clear goal: to keep global temperatures from rising more than 2°C above pre-industrial levels. But that's not only that – there's also a strong push to limit the increase to just 1.5°C.

The reason behind striving for the 1.5°C target is that it represents a safe zone within which the majority of climaterelated disasters can be mitigated. The temperature increase is directly linked to the cumulative greenhouse gas emissions released into the atmosphere. By setting these temperature limits, we establish the maximum amount of emissions that the Earth's environment can accommodate.

We're already feeling the effects of climate change today, and we're standing at nearly 1.1°C above pre-industrial levels. Crossing the 1.5°C threshold would have severe consequences for humanity, wildlife, and ecosystems. Hence, the urgency to take action and reduce greenhouse gas emissions to avoid reaching that dangerous level.

Source: China Dialogue

Scientists compare climate change impacts at 1.5C and 2C

https://www.carbonbrief.org/scientists-compare-climate-change-impacts-at-1-5c-and-2c/

EMISSIONS, EXPLAINED

GREENHOUSE GAS EMISSIONS

Greenhouse gas emissions (GHG) encompass the total sum of emissions of various gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). These gases are released into the atmosphere as a result of human activities such as burning fossil fuels, deforestation, and agricultural practices.

The issue with greenhouse gases is that they have the ability to trap heat in the Earth's atmosphere. As more GHG emissions are released, more heat accumulates in the atmosphere, leading to changes in the Earth's climate system. These changes include rising global temperatures, sea level rise, and an increase in the frequency and intensity of extreme weather events.

Additionally, it is worth noting that different greenhouse gases have varying capacities to cause warming, and they persist in the atmosphere for different lengths of time. To facilitate a standardised measurement of GHG emissions, a metric called "carbon dioxide-equivalents" or CO2eq is used. This metric attempts to combine the warming impacts of different greenhouse gases into a single measure, allowing for a comprehensive assessment of total greenhouse gas emissions.

Source: Our World in Data

CO2 EMISSIONS

Carbon dioxide (CO2) emissions are the largest contributors to greenhouse gas GHG emissions, accounting for approximately 75% of the total. These emissions primarily result from activities such as burning coal, oil, and gas for energy production, manufacturing cement, and the consumption of solid, liquid, and gaseous fuels.

In terms of air transport, it is estimated that it contributes around 2% of global CO2eq emissions. Within the sector, approximately 81% of emissions come from passenger travel, while 19% originate from freight transportation.

Regarding passenger aviation, it is generally recognized that around 60% of emissions stem from international travel, while the remaining 40% come from domestic flights. However, it's important to note that specific percentages may vary depending on the data source and methodology used for estimation.

Source: Our World in Data

NON-CO2 EMISSIONS

Non-CO2 emissions encompass all emissions other than carbon dioxide. These emissions include gases such as nitrogen oxides (NOx), which contribute to the formation of ozone and have a warming effect on the atmosphere. Particulate matter (PM) is another type of non-CO2 emission that can impact air quality and human health.

In the context of aviation, non-CO2 emissions are a significant factor in the industry's environmental impact. These emissions are targeted for reduction through the implementation of cleaner technologies and the adoption of alternative fuels.

By addressing non-CO2 emissions, the aviation sector aims to mitigate its overall environmental footprint and promote more sustainable practices.

SCOPE 1, 2 AND 3 EMISSIONS

Scope 1 emissions: Direct greenhouse gas emissions from sources that are owned or controlled by an organisation.

For airlines, this includes emissions from fuel combustion on the ground and in flight, as well as emissions from other operations, such as maintenance and ground handling. Monitoring and reducing Scope 1 emissions is a key strategy for addressing the environmental impact of aviation and promoting sustainability in the industry.

Scope 2 emissions: Indirect greenhouse gas emissions resulting from the consumption of purchased electricity, heat, or steam.

For airlines, Scope 2 emissions would include emissions from electricity or heat produced at airports, as well as emissions from electricity used for other operations such as office buildings or data centres.

Scope 3 emissions: Indirect emissions from sources outside an organisation's control, such as emissions from the production and transportation of purchased goods and services.

For airlines, Scope 3 emissions include emissions from the production and transportation of jet fuel, as well as emissions generated during the manufacturing and maintenance of aircraft and other equipment.

Source: Getty Images

WHAT ABOUT CONTRAILS?

Contrails, also known as condensation trails, are the visible trails left behind by aircraft in the sky. They form when the hot exhaust gases emitted by aircraft engines mix with the cold air at high altitudes. This mixture causes the water vapour present in the exhaust gases to condense into visible ice crystals or water droplets, along with other particles. While contrails themselves are not greenhouse gas emissions, they have an impact on the climate. Contrails can persist in the atmosphere for varying lengths of time, sometimes expanding and forming cirrus-like clouds. These contrail-induced cirrus clouds have the potential to trap heat radiated from the Earth's surface, contributing to a warming effect in the atmosphere. This impact on the climate system is often referred to as "contrail-induced radiative forcing."

It is important to note that the overall contribution of contrails to climate change is still a subject of scientific research and ongoing study. Nonetheless, the potential impact of contrails on the climate is a recognized area of concern and is being investigated for better understanding and potential mitigation strategies.

UK-based company Satavia, founded by volcanologist and entrepreneur Adam Durant, is working on a solution to significantly reduce the impact of contrails.

Using a weather prediction model, Satavia identifies flights likely to produce contrails and modifies their flight paths, avoiding atmospheric areas prone to contrail formation. This strategy targets only a small proportion of flights (5-10%) that are responsible for most of the contrail climate impact.

The first commercial flight using Satavia's technology took off in October 2021 with UAE's Etihad, with further trials planned with Dutch operator KLM. Studies suggest that diverting just 1.7% of flights could reduce contrail climate damage by 59%. However, regulatory adjustments and industry-wide collaboration will be necessary to fully realise these strategies.

• Also listen to our podcast with former Group CEO of Etihad Tony Douglas.

Source: CarbonBrief

MEASURING CARBON

CARBON INTENSITY

Carbon intensity refers to the measure of how clean or environmentally friendly a particular source of consumed electricity is. It is typically expressed as the amount of CO2 emissions produced per unit of energy consumed.

A lower carbon intensity indicates a cleaner and more sustainable energy source. It means that the electricity generation process associated with that energy source emits fewer greenhouse gases into the atmosphere.

CARBON FOOTPRINT

A carbon footprint refers to the total amount of CO2 emissions released into the atmosphere as a result of the activities of an individual, organisation, event, product, or nation-state.

It encompasses emissions generated throughout the lifecycle of goods and services, including production, transportation, and use. Additionally, it includes emissions from energy consumption, waste disposal, and other relevant activities.

CARBON BUDGET

Carbon budget refers to the cumulative finite amount of CO2 emissions that are estimated and permitted to keep within a certain temperature threshold over a period of time. It is an approach for individuals, businesses and nations to frame the challenge of keeping global warming to ‘acceptable’ levels.

When we spoke to Cirium CEO Jeremy Bowen on our podcast, he emphasised that carbon budgeting will become mainstream in the near future.

He believes that sustainable aviation will require carbon budgeting –specifically in the corporate sector. Just as corporations have traditionally managed travel budgets, they are likely to start considering strict carbon budgets as well.

“So when they’re booking online, they can go right, well, I can fly that business class seat, or I can trade down because I’m running out my carbon budget”, explains Bowen.

• Listen to our podcast.

DECOUPLING

Decoupling refers to the separation or reduction of negative environmental impacts from economic growth. The concept of decoupling was included as one of the main objectives in the OECD Environmental Strategy for the First Decade of the 21st Century, adopted in 2001.

There are two types of decoupling: absolute and relative decoupling.

• Absolute decoupling occurs when the rate of environmental pressure, such as resource use or pollution, remains stable or decreases while the economic growth continues.

• On the other hand, relative decoupling happens when the growth rate of the environmental pressure is positive but slower than the growth rate of the economic variable.

Decoupling can be measured by decoupling indicators, which divide an environmental pressure variable by an economic variable. In some cases, population growth or other variables can serve as the denominator or driving force.

NET ZERO

Net zero refers to a state where the total GHG emissions emitted are equal to the amount removed from the atmosphere.

Achieving net zero requires actively reducing emissions through measures such as efficiency improvements, electrification, and the use of renewable energy sources. It involves both emission reductions and removals, ensuring that a business or organisation operates in a way that does not contribute to climate change.

CARBON NEUTRALITY

On the other hand, carbon neutrality can be claimed by measuring CO2 emissions and offsetting the balance through financing external projects that remove or reduce emissions. It does not necessarily require the business to reduce its own emissions directly.

Carbon neutrality often focuses on the accounting and offsetting of emissions, where emissions are compensated for through activities such as investing in renewable energy projects or supporting carbon capture and storage initiatives. The reporting boundary for carbon neutrality may include a wider value chain, but it is not mandatory to include Scope 3 emissions.

TRUE ZERO

True zero pertains to emissions produced from a specific product or service, where no carbon is emitted from the initial stage – meaning there is no need to capture or offset carbon emissions because the product or service is designed to be carbon-free from the start.

DIFFERENCE BETWEEN A NET-ZERO AIRLINE AND A CARBON NEUTRAL AIRLINE

This is because carbon neutrality is easier to achieve with the existing tools and systems and can be done through offsetting without necessarily requiring changes to other processes. Therefore, airlines are setting interim goals by 2023 or 2040 where the focus is primarily on addressing CO2 emissions through operational efficiencies or carbon offsetting initiatives.

Net zero is a more ambitious goal usually set for 2050 or 2060 by when all airline emissions would effectively be cancelled out by activities that avoid, remove or reduce all greenhouse gases, not only CO2. Of course, this requires significant investment, technological and operational changes, such as the global supply of SAF and the adoption of next-generation aircraft.

It's worth mentioning that while carbon offsetting can help companies reduce their overall carbon footprint, it is still going to be a controversial practice. Some critics argue that offsetting allows companies to buy their way out of their environmental responsibility and that it could be more effective for companies to reduce their emissions directly.

10 AIRLINE PATHWAYS TO NET ZERO

Airlines can aim for net zero emissions via a variety of pathways:

1. Fuel efficiency: It can be achieved through a range of measures, including streamlining operations, optimising flight paths, upgrading aircraft to more fuel-efficient models, and improving load management.

2. Sustainable alternative fuels: biofuels or synthetic fuels made from renewable energy sources can substantially reduce the carbon emissions from flights. Hydrogen is also a potential zero-emission fuel source, although it presents significant technical challenges.

3. Electrification and hybridisation: Electric planes powered by batteries or hybrid planes which combine electric power with conventional jet fuel have the potential to provide zero-emission or low-emission alternatives. However, these technologies are currently only viable for short-haul flights due to limitations in battery capacity.

4. Technology advancements: Advancements in aerodynamics, lightweight materials, and more efficient engines can help reduce fuel consumption and emissions.

5. Air traffic management (ATM): Collaborative efforts between airlines, aviation authorities, and technology providers along with enhanced ATM systems can optimise flight routes, reduce congestion, and minimise fuel burn.

6. Carbon offsetting and carbon capture: Airlines can compensate for their emissions by supporting projects that remove or reduce CO2 elsewhere, such as reforestation initiatives or

investments in renewable energy

Academics and activists have suggested that “demand change” (through increased prices via frequent flyer levies or carbon taxes) is a major pathway to net zero. The industry, however, believes flying is a net good and other pathways need to be explored instead.

ENVIROMENTAL, SOCIAL AND GOVERNANCE

Environmental, Social, and Governance is a management framework that helps stakeholders understand how an organisation is managing risks and opportunities related to environmental, social, and governance criteria (sometimes called ESG factors). It provides a holistic view that sustainability extends beyond just environmental issues. While ESG is often used in the context of investing, stakeholders include not just the investment community but also customers, suppliers, and employees, all of whom are increasingly interested in how sustainable an organisation’s operations are.

OVERVIEW OF E, S AND G

• Environmental: This is about how the company is affecting nature. Are they polluting a lot? Are they using a lot of energy or water? Are they doing anything to help the environment?

• Social: This looks at how the company treats people. This includes everyone from their employees to their customers to the communities where they operate. Are they a good place to work? Are they fair to their customers? Are they helping their communities?

• Governance: This is about the company's leadership. Are they running the company in a fair and responsible way? Are they transparent about their actions? Are they following all laws and regulations?

Source: Net0

Delta Air Lines, one of the largest airlines in the world, has been publishing annual ESG reports since 2009. In its latest 2022 ESG report, Delta illustrated how the airline is holding itself accountable to create a safer, more equitable workplace that reflects the communities it serves while pushing forward a more sustainable future.

Some of the highlighted areas include:

• Delta's commitment to successfully integrate, adapt and improve its safety training and management programs, and develop new safety leaders in the operation.

• Its laser-focus on investing in talent – both financially and enhancing holistic employee wellness – while striving to foster a diverse, equitable and inclusive environment.

• Overview of its accelerated sustainability strategy that features dual pillars of embedding sustainability in everything it does and eliminating its climate impact from flying. This strategy is underpinned by aspirational goals for 2050 as well as a series of incremental milestones along the way to measure progress.

• Listen to our podcast interview with Delta's VP for International Customer Experience and Partner Sustainability, Amelia DeLuca to learn about the airline’s collaborative vision for sustainability.

Source: Delta Air Lines

PASSENGER-FACING INITIATIVES

FREQUENT FLYER TAX

A frequent flyer tax is a levy proposed to be imposed on individuals who travel by air frequently, with the intention of reducing the environmental impact of aviation. The concept is based on the principle of "polluter pays," suggesting that those who contribute more to aviation's carbon emissions should bear a greater portion of the cost.

Benefits of a frequent flyer tax include potentially reducing the number of flights and associated emissions, encouraging more sustainable travel behaviour, and addressing the inequality of aviation's environmental impacts, as a small percentage of people tend to account for a large portion of air travel.

Could it really work?

The idea behind these taxes is that the wealthy minority take the majority of flights, and therefore are responsible for a significant share of aviation emissions.

Last year, the International Council for Clean Transportation (ICCT) published a proposal for a global frequent flyer levy. The proposal involves a progressive tax, suggesting that the first flight would be free, the second would amount to a surcharge of $9, and the cumulative tax going up to ~$177 for the twentieth flight.

• Read our article where we analyse the ICCT’s proposal and discuss its probable implications.

Source: Virgin Atlantic

GREENWASHING

Greenwashing is the practice of making misleading or unsubstantiated claims about the environmental benefits of a product, service, or company. It is often used to create a false impression of environmental responsibility and to appeal to consumers who are concerned about sustainability. Greenwashing can undermine legitimate efforts to promote sustainability and can ultimately harm the environment by encouraging unsustainable consumption.

The aviation industry has been accused of greenwashing claims, as climate activists put ‘big aviation’ in the same league as notorious ‘big oil’. They also perceive airline advertising as promoting overconsumption and planet-damaging growth. Industry insiders, however, often remain perplexed by these actions, extending the argument that air travel accounts for only 2%-3% of global emissions.

*greenhushing – a closely related term is ‘green-hushing’ wherein companies preempt greenwashing accusations by undercommunicating or refraining from publicly talking about their sustainability initiatives. They do this out of fear of being shamed or deemed boastful.

Our ‘Avoiding the Greenwashing Trap’ report looks at how and why climate activists are starting to target airlines, what their main claims are, and how airlines are often getting it wrong.

• Learn more about greenwashing in our podcast episode with our Head of Sustainability, Dirk Singer.

FLIGHT SHAMING

Flight shaming is a movement that encourages people to avoid air travel due to its negative impact on the environment. The movement seeks to raise awareness of the high levels of greenhouse gas emissions associated with air travel and to promote alternative modes of transportation, such as trains.

Why do climate change activists focus so much on aviation?

In December 2022, the German climate change group "Letzte Generation" (Last Generation) staged protests at Munich and Berlin airports, indicative of escalating environmental activism targeting the aviation industry. Such actions question aviation's contribution to climate change, despite the sector representing only 2-3% of total emissions.

Core beliefs guiding these movements include the urgency of the climate crisis and overconsumption by the Global North at the expense of the Global South. As such, aviation is critiqued as a form of conspicuous, polluting consumption, with a minority of frequent flyers accounting for a significant share of emissions. Critics also contend that airline marketing strategies fuel excessive demand.

Activists propose measures like health warnings on airline ads, flight caps, and frequent flyer taxes, and they express scepticism toward the industry's sustainability initiatives. The focus on aviation, they argue, is both justified and necessary in the face of the climate emergency.

• Read our detailed analysis of why there’s growing activism against the airline industry.

CIRCULAR ECONOMY

The circular economy is a model of production and consumption, which involves sharing, leasing, reusing, repairing, refurbishing and recycling existing materials and products as long as possible. In this way, the life cycle of products is extended.

It aims to create closed-loop systems where materials and products are reused and regenerated, rather than discarded. By prioritising sustainability and resource efficiency, the circular economy offers a pathway towards a more sustainable and resilient future.

The linear economic model – take, make, dispose – is wasteful. The circular economy aims to reduce waste by maximising the lifecycle of products through reuse, recycling, and repurposing, which is a crucial concept to reaching net zero in aviation.

One cabin waste audit indicated already in 2012 and 2013 that a typical passenger generated 1.43 kilos of cabin waste, of which 23% was untouched food and drink and a further 17% composed of recyclable materials (e.g. plastic bottles and newspapers).

Another research by IATA indicated that in 2017 the sector generated 5.7 million tonnes of cabin waste and with current passenger growth rates, this waste volume could double in the next 10 years.

One of the main challenges airlines face when it comes to reusing and recycling is the regulatory structure of the industry:

• Many governments have implemented the International Catering Waste (ICW) legislation to minimise the risk of spreading animal and plant diseases.

• While airline meals are prepared with high standards of hygiene and quality control, originally designed for NASA astronauts, these regulations often result in the incineration of all cabin waste, making it difficult to reuse and recycle.

• Because cabin waste is collected and managed by two different contractors (cleaners and caterers), undertaking a holistic cabin waste composition analysis is challenging for airlines.

While IATA advocates the adoption of smarter regulation, it is crucial for airlines to prioritise environmental mindfulness and not shift the blame to consumers.

In fact, this is where academia can make a huge impact. Implementing academic knowledge for sustainable growth can lead to collaborative efforts towards a sustainable future.

• Listen to our podcast episode with Ramon Sanchez, Principal Investigator and Research Associate at Harvard University to learn more about the circular economy and its relevance to sustainability.

Can aviation really embrace the circular economy?

CARBON OFFSETTING

Carbon offsetting is a method by which companies compensate for their carbon emissions by investing in environmental projects that reduce carbon dioxide in the atmosphere. The benefits include flexibility for businesses to reduce their carbon footprint and support for sustainable projects.

However, it is criticised for potentially enabling companies to avoid reducing their actual emissions. Critics argue it's a form of greenwashing, allowing businesses to appear environmentally friendly without making substantial changes.

When should carbon offsetting be used?

Carbon offsetting often treats nature as a replaceable service provider and embodies "weak sustainability," which implies natural and manufactured capital can be swapped, ignoring potential environmental damage.

Many offsets fail to deliver on their promises, leading to ineffective climate action. Critics urge that carbon offsetting should be a last resort and urge businesses to focus on reducing their emissions.

• Principles to follow when using offsets include:

• A thorough evaluation of the programme

• Not choosing based on price alone

• Avoiding deforestation protection credits

• Focusing on local projects

• Transparent communication about the role of offsets

• Continually working towards net zero emissions

While offsetting companies like CarbonClick show more accountability, moving away from reliance on offsetting is crucial for our planet.

• Learn more on our podcast episode with CarbonClick’s Vice President of Enterprise Product & Strategic Partnerships, Seth Horowitz.

CARBON REMOVAL

While strategies to reduce emissions are important, they will not be enough to reach the net zero emissions targets. Reaching these goals requires strategies that actively remove CO2 from the atmosphere.

In essence, carbon removal refers to a process where CO2 is captured from the atmosphere and stored for decades or centuries through different means, e.g., in trees, soils, underground reservoirs, rocks, the ocean and even products like concrete. There are three key carbon removal strategies:

• Natural strategies like tree restoration and agricultural soil management. Natural strategies are the single largest “shovel-ready” opportunity for carbon removal at scale in the US.

• High-tech strategies like direct air capture (DAC) that use chemical reactions to capture CO2 from the atmosphere. DAC is gaining traction as a promising carbon removal approach.

• Hybrid strategies like enhanced root crops or bioenergy with carbon capture and storage (BECCS).

The key benefit of carbon removal is its potential to reverse emissions, not just reduce them, which is crucial to mitigating climate change and achieving net-zero emissions targets.

It also allows for the continued use of carbon-intensive technologies, making the transition to a low-carbon economy more manageable.

Source: World Resources Institute

Source: MIT Technology Review

Carbon Capture vs Direct Air Capture: What’s the difference?

• Direct air capture and storage (DAC+S) captures CO2 directly from the air, reducing the atmospheric concentration of CO2.

• In contrast, carbon capture and storage (CCS) is a process that intercepts CO2 emissions from industrial sources – such as power plants and factories – and prevents them from entering the atmosphere. The captured CO2 is then stored underground.

Source: Climeworks

Both strategies aim to mitigate the effects of CO2 on climate change, but they target different sources of emissions and use different methods.

• Read our report on some of the most exciting companies to watch out for in this space.

Source: Air Company

Air Company has developed its proprietary AIRMADE™ technology that imitates the recipe of photosynthesis using only three inputs: air (carbon dioxide), water, and sun or wind (renewable energy). Through a complex process, it transforms carbon dioxide into sustainable alcohols and fuels – leaving just oxygen as a byproduct.

These CO2-based alcohols and fuels are then applied to a variety of consumer and industrial products. For example, Air Company's CO2-derived, 100% unblended jet fuel has been approved and flown by the US Air Force.

With similar endorsements from other industry players like NASA, Virgin Atlantic, and JetBlue, Air Company is poised for growth.

• Listen to our podcast episode with the co-founder of Air Company, Gregory Constantine to learn more.

Source: Air Company

IATA NET ZERO RESOLUTION

The International Air Transport Association (IATA) represents most of the world's airlines, making it a powerful platform for international collaboration and coordination.

By setting a target for net-zero carbon emissions, the IATA acknowledges the urgent need to address climate change and mitigate the industry's impact on the environment.

The IATA Net Zero Resolution provides a roadmap that is focused on delivering a maximum reduction in emissions at source through four key elements:

• The use of sustainable aviation fuel, sourced from feedstocks that do not degrade the environment or compete with food or water

• Investment in new aircraft technology, including radical new aerodynamic and alternative propulsion (electric or hydrogen) solutions

• Continued improvement in infrastructure and operational efficiency, with a particular focus on improved air traffic management

• The use of approved offsets including carbon capture and storage technology

As more investors, customers, and communities expect businesses to prioritise sustainability, the resolution encourages global aviation's commitment to combating climate change head-on.

Will it really work?

While the Net Zero Resolution is laudable, it will be challenging to achieve and has attracted criticism from various quarters. Here are some of the key challenges and criticisms:

1. Dependence on offsetting: The IATA's plan heavily relies on carbon offsetting - that is, investing in projects that remove or reduce CO2 elsewhere to compensate for the emissions produced by flights. Critics argue that offsetting is not a long-term solution and does not encourage enough reduction in emissions at the source. Some also question the effectiveness and accountability of offset projects.

2. Scope of emissions: While the IATA's net-zero target includes CO2 emissions from flights, it does not cover non-CO2 emissions, such as those from contrails and nitrogen oxides. Furthermore, it does not cover emissions from the production of aviation fuels or the manufacturing and disposal of aircraft.

3. Over-reliance on future technologies: Next-generation aircraft are not yet mature or economically viable at the necessary scale. There's a risk that the industry won't be able to scale up these technologies as fast as needed to meet the net-zero target.

4. High hosts: Transitioning to SAF and new technologies will be expensive. This is a significant challenge in an industry with historically thin profit margins and one that has been hit hard by the COVID-19 pandemic. There's also the question of who will pay for these changes - airlines, passengers, governments, or some combination of the three.

5. Regulatory and policy challenges: Coordinating the required changes and getting buy-in from all stakeholders can be a complex and time-consuming process.

6. Equity concerns: Some critics argue that the IATA's plan does not adequately address equity concerns. For example, carbon offsetting projects often take place in developing countries, which can lead to issues around land use and the rights of local communities. Similarly, if the costs of the transition to net zero are passed onto passengers in the form of higher ticket prices, this could make air travel less accessible for some people.

CORSIA

The Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) is a programme designed to help the aviation industry reduce its carbon emissions. It's been set up by the International Civil Aviation Organization (ICAO), a group that oversees international air travel.

In simple terms, CORSIA works like this: imagine you're an airline, and your planes give off a certain amount of CO2 when they fly. Under CORSIA, if your flights give off more CO2 than a set limit, you need to make up for it. You do this by investing in projects that reduce CO2 elsewhere, like planting trees or creating renewable energy (i.e., carbon offsetting).

CORSIA aims to ensure that any growth in international flights after 2020 doesn't lead to a rise in total CO2 emissions from the industry. The idea is to encourage airlines to cut their emissions where they can and offset the rest.

Benefits of CORSIA

1. Global impact: It is the first global scheme aimed at reducing CO2 emissions from a single industry. This is a big deal, given how much carbon dioxide is given off by planes.

2. Encourages cleaner technologies: By setting a limit on CO2 emissions, CORSIA encourages airlines to use cleaner technologies and fuels.

3. Flexible compliance: Airlines have flexibility in how they meet their offsetting requirements. They can reduce their own emissions, buy carbon credits from other airlines, or invest in offset projects.

Criticisms of CORSIA

1. Dependence on offsetting: Critics argue that CORSIA relies too much on offsetting rather than on actual reductions in emissions. Offsetting projects can be complex and expensive. With offsets under CORSIA costing, about as low as €2.40 per passenger, for a long haul flight, their effectiveness is often questionable.

2. Voluntary participation: CORSIA's first few years are voluntary, and not all countries are participating. This means a significant amount of aviation emissions may not be covered by the scheme

3. Limited scope: CORSIA only applies to international flights and not to domestic ones. As such, a large proportion of global aviation emissions are not covered.

4. No non-CO2 emissions: CORSIA does not cover non-CO2 emissions, like those from contrails and nitrogen oxides, which also contribute to global warming.

Source: ICAO

SBTi

Founded in 2015, The Science Based Targets initiative (SBTi) is a global body that aims to help companies and financial institutions set greenhouse gas emissions reduction targets in line with the goals of the Paris Agreement.

In essence, the SBTi shows organisations how much and how quickly they need to reduce their greenhouse gas emissions to prevent the worst effects of climate change. SBTi defines targets as ‘science-based’ if they provide a clearly-defined pathway, in accordance with the latest scientific findings.

The SBTi, however, has been criticised for not being transparent about its methods. Once a target has been validated by the SBTi, there is no obligation for companies to follow through on the goals. While companies are required to explain their cause, failure to achieve a target does not amount to any penalty. The SBTi is currently working towards revising its framework to overcome its shortcomings.

The SBTi stamp of approval is quite popular amongst airlines, with airlines like Air New Zealand, American Airlines, easyJet, Air France - KLM, and several others already committed to the cause.

In our ‘Flying to Net Zero’ report, we interviewed easyJet’s Sustainability Director, Jane Ashton, who explained the airline’s net zero strategy via the SBTi.

• Read our report.

Source: SBTi

THE EU EMISSIONS TRADING SYSTEMS (ETS)

Set up in 2005, the EU ETS (European Union Emissions Trading System) is the world’s first international emissions trading system. It is a type of carbon market, often referred to as a "cap-and-trade" system, which aims to reduce greenhouse gas emissions through market mechanisms.

Key elements of a cap-and-trade system:

• Cap: The "cap" in cap-and-trade refers to the total limit on greenhouse gases that can be emitted by all participating entities. In the case of the EU ETS, this includes around 11,000 heavy-energy-using installations in power generation, industry sectors and airlines operating between these countries. Each year, the EU lowers the cap slightly, meaning the total emissions from these sectors must reduce accordingly.

• Trade: Each participant (say, a power plant or airline) is allocated a certain number of carbon credits, where each credit represents the right to emit one tonne of CO2 (or the equivalent amount of different greenhouse gas). These allowances can be traded, meaning a company that reduces its emissions and doesn't need all its allowances can sell them to a company that is unable to reduce its emissions as quickly.

• Carbon price: The trading of allowances creates a carbon price, which is the cost per tonne of CO2 emitted. This price is a signal of the value of reducing emissionsthe higher the price, the greater the economic incentive for companies to cut their emissions.

The EU ETS is the largest carbon market in the world, but it's not the only one. There are several others, including the California Cap-and-Trade Program, the Regional Greenhouse Gas Initiative (RGGI) in the northeastern United States, and the Chinese national carbon market. Each of these operates similarly to the EU ETS, but with different caps, participants, and regulations.

Source: Maersk

Relevance to Aviation

Trading CO2 emissions from aviation is available in the EU ETS since 2012. Under the EU ETS, all airlines operating in Europe are required to monitor, report and verify their emissions, and to surrender allowances against those emissions.

The benefits of including aviation in the EU ETS:

• Encourages emission reduction: It incentivizes airlines to reduce their greenhouse gas emissions, as they can profit from selling unused credits.

• Global impact: As many airlines operate internationally, this means that the benefits of emission reductions can have a global impact, not just within the EU.

• Market-based solution: The system harnesses market mechanisms to drive environmental improvements, which can often be more efficient than command-andcontrol regulation.

Ryanair has been actively participating in the EU Emission Trading System (ETS) since 2012 as required by law. Initially, like many other airlines, Ryanair voiced concern over the EU ETS, primarily over fears of increased operational costs which would translate to higher airfares. The company expressed that the implementation of the system would give non-European airlines a competitive advantage.

To meet the EU ETS requirements, Ryanair has invested in newer, more fuel-efficient aircraft and has pursued a high-seat-density model, which spreads the emissions from each flight over a larger number of passengers. They have also invested in digital tools and carbon offsetting projects.

However, some environmental groups have criticised these efforts as inadequate, arguing that the only effective way to reduce emissions from aviation is to reduce the number of flights. In 2019, Ryanair, the Irish low-cost airline, became the first non-coal company to join the top ten list of EU's biggest carbon dioxide emitters, highlighting the significant emissions that can come from aviation.

Source: The Times

Sustainable aviation fuels (SAF) represents a broad category of fuels derived from nonfossil sources, including advanced biofuels and e-fuels, offering a sustainable alternative to conventional jet fuel.

IATA estimates that SAF could contribute approximately 65% of the emissions reduction necessary for aviation to achieve its goal of reaching net zero CO2 emissions by 2050.

BIOFUELS (BAF)

Biofuels, also known as biojet or renewable jet fuel, are derived from biomass sources such as plant materials (vegetable oils, algae), animal waste, and certain sugars and starches. They can be produced using various conversion technologies.

Biofuels offer several benefits, including a significant reduction in greenhouse gas emissions compared to conventional fuels, utilisation of renewable feedstocks, and potential for waste and byproduct utilisation.

However, limitations include high production costs, limited availability of sustainable feedstocks, and lower energy density compared to conventional fuels. To be used in aviation, biofuels have strict compositional requirements that go beyond those for road transport fuels. Therefore, BAF is currently blended with fossil fuel-derived jet fuel which allows it to meet the needs of aviation fuel while reducing the overall carbon footprint of the fuel. (source)

Source: Genetic Literacy Project

SYNTHETIC FUELS

Synthetic fuels, also known as e-fuels or electrofuels, are produced by combining captured carbon dioxide emissions with hydrogen derived from renewable energy sources like solar or wind power.

E-fuels offer advantages such as zero or low net carbon emissions when produced using renewable energy and the potential for carbon dioxide recycling. However, challenges include high production costs, energy-intensive production processes, and the need for large-scale infrastructure and investment.

Source: Inhabitat

The pros of SAF

1. Reduced greenhouse gas emissions: SAF can reduce CO2 emissions by up to 80% compared to conventional aviation fuels.

2. Renewable and sustainable: SAF does not compete with food crops or water supplies, nor does it contribute to forest degradation. Unlike fossil fuels, SAF can actually recycle CO2 that has been absorbed by the biomass used in the feedstock during its lifetime. (source)

3. Technological compatibility: SAF is a “drop-in” fuel which can be used on today's aircraft without modifications when blended with up to 50% conventional jet fuel.

4. Potential for waste and byproduct utilisation: BAF can be produced from waste materials, offering an opportunity for waste reduction and circular economy principles.

The cons of SAF

1. Production costs: At the moment, SAF is still more expensive compared to conventional fuels, hindering widespread adoption and scalability.

2. Feedstock availability: Sourcing sustainable feedstocks in sufficient quantities without competing with food crops or causing environmental harm is very challenging.

3. Energy density: SAF generally have lower energy density than conventional fuels, which can affect aircraft range and performance.

4. Scale and infrastructure: Scaling up SAF production and establishing the necessary infrastructure for production, distribution, and storage require substantial investment and coordination among stakeholders.

BOOK AND CLAIM

Book and claim is a system for tracking the production and use of SAF. It allows airlines to purchase SAF credits from producers, verifying that the fuel has been produced sustainably. The credits can then be used to offset the emissions from their flights. This system provides a market-based incentive for the production and use of SAF and can help to accelerate the transition towards a more sustainable aviation industry.

The book and claim system also claims to boost the demand and supply of SAF, hence bringing down its exorbitant costs. Last year, Amex GBT partnered with oil bigwig Shell to launch the world’s first blockchain-powered platform called Avelia. The program offers around 1 million gallons of SAF, which will be certified according to the regulatory standards set by the country of delivery. Aon was the first customer to join Avelia.

• Learn more about Amex GBT’s Avelia program in our interview with Amex GBT’s Vice President of Global Sustainability, Nora Lovell Marchant.

Source: American Express GBT - Twitter

RENEWABLE ENERGY

Renewable energy refers to energy obtained from naturally replenishing sources that are abundant in nature, such as sunlight, wind, water, geothermal heat, and biomass. It is considered an important tool for achieving sustainable development and reducing greenhouse gas emissions.

Renewable energy technologies are rapidly advancing and becoming more cost-effective, making them increasingly competitive with traditional fossil fuels.

Aviation's green revolution

Airlines and airports around the world have been implementing various initiatives to reduce their environmental impact. Here are some interesting milestones:

• In 2011, KLM carried out the world’s first commercial flight partly powered by SAF made from used cooking oil.

• In 2012, Galapagos Ecological Airport (Ecuador) became the world's first environmentally sustainable terminal running solely on solar (35%) and wind power (65%), with 80% of its infrastructure made from recycled materials.

• In 2015, Cochin International Airport (India) became the world's first fully solarpowered airport in 2015. Its solar plant has more than 46,000 solar panels generating approximately 60,000 units of electricity daily.

• In 2022, Indianapolis International Airport (USA) worked with Canadian company Carbon Cure to lay a runway where the concrete has recycled CO2 injected into it.

• In late 2023, Virgin Atlantic aims to perform the first-ever transatlantic flight from London to New York using 100% SAF.

• Edmonton International Airport (Canada) is creating the largest airport-based solar farm in the world.

• Learn more about airports using renewable energy and reducing their carbon footprint, in our interview with Dubai Airport’s CEO, Paul Griffiths.

Source: Embraer

URBAN AIR MOBILITY (UAM)

Urban Air Mobility (UAM) is a new air transportation system for passengers and cargo in and around densely populated and built-up environments, made possible by small, electric vertical takeoff and landing aircraft (eVTOL).

UAM is seen as a potential solution to urban congestion, reducing travel times and emissions while increasing mobility. However, the development and deployment of UAM require significant technological, regulatory, and infrastructure challenges to be overcome.

Considering the excitement around UAM, several big airlines are forming partnerships and placing pre-orders with different companies.

• Our UAM Power List report unpacks the hype behind these aircraft and identifies their possible use cases.

eVTOL

Electric vertical takeoff and landing (eVTOL) aircraft are small aircraft that are capable of vertical takeoff and landing, similar to helicopters. However, eVTOLs are powered by batteries or fuel cells, making them much quieter and more efficient than traditional helicopters.

They have the potential to revolutionise urban transportation by providing fast, efficient, and environmentally friendly transportation options for short-range trips.

Popularly known as ‘air taxis’, eVTOLs promise to bring all our Jetsons dreams true by changing the nature of flying itself. American aerospace company Archer Aviation focuses on designing and developing eVTOLs, which they believe will “unlock the skies”, and enable everyone to reimagine how they live, travel and manage time. Other notable eVTOL manufacturers are Joby, Eve, Supernal and Wisk.

• Read our article about how the introduction of eVTOLs can transform aviation, based on a discussion at this year’s SXSW Festival.

Source: Archer

REGIONAL AIR MOBILITY (RAM)

Urban Air Mobility (UAM) and Regional Air Mobility (RAM) are emerging paradigms in aviation, though they serve distinct geographical and functional scopes.

While UAM focuses on improving connectivity within dense, urban areas, RAM extends beyond city limits and is targeted towards regional transportation. It focuses on connecting cities, towns, and other geographical areas within a region, usually within a range of about 100 to 500 miles.

RAM vehicles can be larger and potentially hybrid, due to the longer distances involved. The goal is to provide a faster, more efficient mode of transportation between regional locations, making use of existing small and medium-sized airports and reducing reliance on ground transportation or major airline hubs.

Regional Air Mobility is likely to be driven largely by electric and hydrogen (along with hybrid versions) aircraft.

ELECTRIC AIRCRAFT

Electric aircraft are planes that run on electric power instead of fuel. The idea is similar to electric cars. Just like how an electric car uses batteries to power the motor, an electric aircraft uses batteries to run its propellers.

There are multiple benefits of electric aircraft:

• They are non-polluting and do not release greenhouse gases. As a result, they can reduce air pollution and fight climate change.

• Electric planes could be cheaper to run because electricity can cost less than jet fuel.

• They will likely be easier to maintain and operate, reducing the lifetime costs of the plane.

• Finally, they are expected to be significantly quieter than jet and propeller planes, reducing noise pollution and making them capable of flying to many airports without community-based restrictions.

However, there are also challenges with the biggest one being the battery. Batteries for electric aircraft need to be light, but they also need to store a lot of energy which is hard to accomplish with today's technology. For example, the energy density of the best batteries available today is nearly 20 times lower than conventional jet-A fuel.

Another significant hurdle is that electric planes need a place to charge their batteries, just like electric cars. Creating such an infrastructure can be challenging and expensive.

Source: Lilium

While the technology for electric long-haul travel is still far off, for short-haul travel electric aircraft, like Heart Aerospace’s ES-30, could prove revolutionary. The 30-seater aircraft includes a reserve-hybrid configuration and is projected to operate with zero emissions and low noise. Commercial passenger flights on the ES-30 are expected to commence in 2028. Other notable electric aircraft manufacturers include Cosmic Aerospace, Maeve and Ampaire

• Learn more about how electric aircraft can transform regional aviation in our interview with Heart Aerospace’s CEO and Founder Anders Forslund.

HYDROGEN AIRCRAFT

Hydrogen aircraft are planes that use hydrogen as a power source. This can be potentially done in two ways:

• To burn the hydrogen in jet engines, much like the kerosene in conventional aircraft.

• To use hydrogen to power a fuel cell, which then produces electricity to drive the aircraft's propellers.

At first glance, hydrogen looks to be a good solution for flying without wrecking the climate. Whether it is used to power a fuel cell to generate electricity or directly combusted for power, the only byproduct is clean water, not greenhouse gases.

Hydrogen is also more energy-dense than traditional aviation fuels – three times more than conventional jet fuel, and more than a hundred times that of lithium-ion batteries

Source: Eviation

But there are big disadvantages with using hydrogen for aircraft:

• One of the main ones is the storage of hydrogen – hydrogen gas takes up a lot of space, even when compressed, which is a problem on an airplane where space is at a premium.

• It also requires very cold temperatures to remain a liquid, adding to the complexity of storage.

• Another challenge is safety – hydrogen is highly flammable, which means it has to be handled and stored very carefully.

• The lack of infrastructure for hydrogen fuel. We would need new systems at airports to store and deliver hydrogen fuel, and that would require major investments.

There's also the fact that most hydrogen currently available is "grey" hydrogen made from natural gas, which isn't environmentally friendly. We would need to significantly scale up production of "green" hydrogen, made using renewable energy, for hydrogen aviation to truly be sustainable.

The State of the Industry

Even though hydrogen performs three times better than conventional jet fuel, using it with traditional aircraft, however, is not as straightforward.

In our podcast, Universal Hydrogen’s co-founder John-Paul Clarke pointed out that aircraft would require significant tweaking of the engines to make the transition to this clean fuel. As a result, aircraft manufacturing startup ZeroAvia has resorted to retrofitting existing aircraft with hydrogen-electric power trains.

Giants like Airbus are betting big and working on clean-sheet aircraft designs that don’t depend on existing technology or infrastructure. In 2020, Airbus revealed three concepts for zero-emission commercial aircraft – all code-named “ZEROe” – that could enter service by 2035.

• Learn more about Airbus’ investments in hydrogen in our interview with the airframer’s Vice President for Research & Tech (Americas), Amanda Simpson.

Source: Airbus

Listen to more insights on our podcast

Want more sustainable aviation insights? Sustainability in the Air is the world’s first sustainable aviation podcast. Hosted by SimpliFlying Shashank Nigam, the show has featured airline CEOs such as Scott Kirby and Tony Douglas.

But as part of the podcast, Shashank has also talked to innovators developing new kinds of aircraft and engines, such as Heart Aerospace CEO Anders Forslund, ZeroAvia CEO Val Miftakhov and Archer Aviation CEO Adam Goldstein.

Listen and subscribe to the podcast here:

green.simpliflying.com/podcast

Guests on previous seasons of the podcast have included Heart Aerospace CEO Anders Forslund, ZeroAvia CEO Val Miftakhov and

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Archer Aviation CEO Adam Goldstein.

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