Five Years to Chart a New Future for Aviation

Executive Summary

The aviation sector is at a pivotal moment in its history. Currently, only about 10% of the global population flies ^[1] Link to footnote , a figure expected to grow as incomes rise. Yet, aviation already accounts for around 2.5% of global CO₂ emissions, and when non-CO₂ effects are included, its contribution to climate warming increases to approximately 4%. Despite ambitious pledges from governments and industry to achieve a net-zero aviation sector by 2050, the sector remains dangerously off track. Without swift and decisive action, we risk missing the opportunity to reach net-zero emissions by 2050 and delaying the crucial technological and business transformations needed.

While global leaders have endorsed a vision of net-zero carbon emissions for the aviation sector, current efforts fall short in both scope and speed. In some cases, proposed solutions could exacerbate the crisis, such as relying too heavily on biomass for jet fuel without managing its environmental impact. It is also crucial to address aviation’s broader climate effects, including the formation of persistent contrails. The stakes have never been higher: urgent action is needed to shift the sector onto a sustainable path.

This report outlines an ambitious five-year plan to chart that course. It establishes four pivotal 2030 Sustainable Aviation Goals, each targeting key leverage points within the sector. If these goals are not implemented immediately and achieved by 2030, the opportunity for transformation will slip away, leaving the world to face the escalating climate impacts of a rapidly growing aviation sector, which is projected to at least double by 2050.

Ambitious Five-Year Plan to Set the Future of Aviation

The five-year plan involves immediately implementing four Sustainable Aviation Goals which provide a plan for delivering net-zero aviation by 2050. These goals originated during the inaugural meeting of the Transatlantic Sustainable Aviation Partnership held at MIT in April 2023, with representatives from the UK, US, and EU. They were further discussed at a roundtable hosted by the Sustainable Markets Initiative in the presence of King Charles III, and previewed at the opening of COP28.

Two goals (Goals 2 and 3) can be achieved with minimal new technology but require robust and clear market signals and swift policy action. The other two goals (Goals 1 and 4) demand immediate efforts to push the boundaries of technology, creating new opportunities from 2030. The four goals are:

Goal 1: Operation Blue Skies

In 2025, governments and industry should create several Airspace-Scale Living Labs to enable a global contrail avoidance system to start to be deployed by 2030. These labs must have the capability to test, learn, and pivot while operating within a realistic airspace environment.

Goal 2: Systems Efficiency

In 2025, leading governments should set out a clear commitment to the market about their intention to drive system-wide efficiency improvements. In tandem, governments and industry should work together to develop strategies so that, by 2030, a new wave of policies can be implemented to unlock these systemic efficiency gains.

Goal 3: Truly Sustainable and Scalable Fuel

In 2025, governments should reform Sustainable Aviation Fuel (SAF) policy development to adopt a cross-sector approach, enabling rapid scalability within global biomass limitations. By 2030, governments and industry should implement a demonstration and deployment strategy that enables SAF production to move beyond purely biomass-based methods, incorporating more carbon-efficient synthetic production techniques.

Goal 4: Moonshots

In 2025, launch several high-reward experimental demonstration programmes to enable the focus on, and scale-up of, the most viable transformative technologies by 2030. These programmes must generate the necessary experience to assess the technology's scalability and develop the expertise required for deployment.

Priority Actions

Two priorities stand out. First, Goal 1: Operation Blue Skies offers a low-cost, high-impact solution with significant potential to reduce aviation’s climate footprint while also providing the opportunity to reduce cloudiness in areas where air traffic is high, as seen during the COVID-19 pandemic when flights were grounded — an outcome likely to be popular with the public. Successfully implementing contrail avoidance could reduce the climate impact of aviation by roughly 40%.

Second, Goal 4: Moonshots represents a once-in-a-generation opportunity for nations to lead in developing new, transformative industries. By investing now in frontier technologies—such as cryogenic hydrogen or methane fuels, hydrogen-electric propulsion, and synthetic biology—governments can unlock opportunities within the aviation sector and across a range of adjacent sectors, much like electric vehicles have reshaped the automotive sector.

Growing awareness and commitment to action are encouraging. Still, it is essential to match those professed concerns with decisive interventions over the next five years to create a credible path to net-zero aviation by 2050.

Chapter 1

Introduction

The aviation sector is at a critical crossroads: it has the potential to drive systemic change, or it could fall behind in the race to achieve net-zero emissions. Building on insights from the Aviation Impact Accelerator’s model this report identifies the most impactful leverage points within the aviation system. These are key areas where targeted interventions can trigger substantial, transformative shifts. The four Sustainable Aviation Goals outlined here are designed to focus on these leverage points, aiming to significantly raise the sector's ambitions and laying a strong foundation for reaching net-zero emissions by 2050.

These goals were first conceived during the inaugural meeting of the Transatlantic Sustainable Aviation Partnership at MIT in April 2023, hosted jointly by the University of Cambridge and MIT, with participation from the UK, US, and EU governments. They were further discussed at a roundtable event organised by the Sustainable Markets Initiative, attended by King Charles III at the Whittle Laboratory in Cambridge, and previewed at COP28. The goals have been deliberately crafted to exceed current industry and governmental targets, with the intention of driving actions that will substantially raise ambition. Each scenario has been rigorously analysed using the Aviation Impact Accelerator model to ensure that it is grounded in robust, evidence-based analysis.

Achieving these goals by 2030 will require bold leadership and coordinated ambition from governments and businesses. This moment is reminiscent of the late 2000s in the automotive industry when the debate over the future dominance of biofuels versus battery-electric vehicles reached its peak. Similarly, the future of aviation remains uncertain—whether the dominant solutions will be Sustainable Aviation Fuels (SAFs) or whether transformative technologies such as cryogenic hydrogen or methane fuels, hydrogen-electric propulsion, or synthetic biology will ultimately supplant them. The 2030 Goals are designed to accelerate this decision-making process, enabling more focused and rapid progress post 2030.

The report concludes by presenting several scenarios that demonstrate how achieving the 2030 Goals can enable the aviation sector to reach net-zero emissions by 2050. It should be noted that all scenarios are based on a business-as-usual baseline, which is detailed in the Emission Baseline section.

Chapter 2

Operation Blue Skies

2030 Goal 1: Operation Blue Skies

Aviation’s climate impact is not just limited to CO₂: aviation’s non-CO₂ climate warming impacts include emissions such as nitrogen oxides, stratospheric water vapour and particulate matter, and the formation of persistent contrails. Of these, persistent contrails have the most significant climate effect. The precise size of their climate impact relative to CO₂ depends on the metric used for comparison, but generally, the impact of contrails and aviation’s CO₂ emissions are of similar magnitude, although the uncertainty in the size of the climate impact of contrail is much greater than for CO₂.

Persistent contrails can be avoided by adjusting an aircraft’s altitude in regions where contrails form, known as Ice Supersaturated Regions (ISSRs). These regions are pancake-shaped—wide but shallow—making altitude changes effective in preventing contrail formation. However, predicting the location of ISSRs is uncertain, and altitude changes can increase fuel consumption by a few percent.

The main challenge in implementing an effective contrail avoidance system lies in the numerous uncertainties, from the underlying science to the variety of potential implementation methods. The ideal way to address these uncertainties is through a learn-by-doing approach in a realistic, field-based environment. To facilitate this, several Airspace-Scale Living Labs must be established by the end of 2025. These Labs must be designed for iteration—capable of testing, learning, and pivoting as experience is gained.

In developing these Labs, it is crucial to draw on experiences from fields where public confidence is paramount, such as medical trials and epidemiology. Each Lab should be designed to represent the real nature of the challenge in a particular region of the world i.e., to capture the full range of weather and flight traffic conditions that are likely to be encountered. The Labs should also be conducted at a scale that accurately replicates real-world complexities while ensuring statistical quality and following a transparent review process.

The objective of the Labs is to develop the experience and strategic planning necessary to start the deployment of a global contrail avoidance system by 2030.

Outcome

The figure below shows the rate at which the Earth is warmed (“Effective Radiative Forcing”, ERF) due to aviation, allowing the comparison of different warming effects including non-CO₂ effects. The black dashed line shows the warming rate due to aviation CO₂ released since 1940, including projections of future aviation CO₂. The solid black line shows the warming effect caused by the combined effect of aviation’s CO₂ emissions and persistent contrail formation. The green region shows the impact on warming of deploying a global contrail avoidance system starting in 2030, after the completion of the Airspace-Scale Living Labs. For interest, an extra line, the black dotted line, has been added, showing just the warming impact of aviation CO₂ currently in the atmosphere.

The figure illustrates that the climate impact of contrails and CO₂ emissions are of similar magnitude. However, it is important to note that the climate impact of contrails carries a high degree of uncertainty, as indicated by the error bar in the figure shown for 2018’s contrails. While only one in 20 kilometres flown produces a persistent contrail, which lasts less than a day, about half of the CO₂ emitted remains in the atmosphere for around 30 years, with a fraction persisting for a millennium. The climate impacts of the two are comparable because, although contrails are short-lived, their effective radiative forcing is several orders of magnitude greater than that of CO₂ released by the flights that cause them ( Key Fact 1 ).

The figure also shows that the effective operational date for a global contrail avoidance system could range from 2039 to 2050, with its effectiveness in avoiding contrails varying between a 50% and 85% success rate. More details on the modelling behind this deployment schedule can be found in Key Fact 2 . The uncertainty in the timeline and effectiveness stems from the nature of the solution itself—specifically, whether a new constellation of Low Earth Orbit (LEO) satellites will be required and the degree of airspace modernisation and policy development necessary. The only way to reduce this uncertainty is through the establishment and operation of the Airspace-Scale Living Labs.

The global deployment of a contrail avoidance system presents four key implementation challenges ( Key Fact 3 ). Focus in these areas is required to accelerate implementation:

Congestion: Many regions have congested airspace, limiting opportunities for contrail avoidance.
Incentives: Although the cost of contrail avoidance could be very low ( 2050 Ticket Cost ), operators need incentives to adopt the necessary behaviours.
Measuring contrail absence: There is a practical challenge in accurately determining whether a contrail would have formed without avoidance measures.
Operational change: Shifting the behaviour of thousands of individuals and introducing new systems will be difficult.

Finally, delaying action poses significant risks. As shown in Key Fact 4 , the warming impact from the extra fuel burned for contrail avoidance is minimal, at least 25 times smaller than the smallest possible climate impact of contrails. Furthermore, implementing a global contrail mitigation scheme could deliver substantial benefits. We estimate that a successful scheme could be equivalent to the one-time removal of 5 to 50 billion tonnes of CO₂ from the atmosphere, representing between 2.5% and 24% of the remaining IPCC global carbon budget needed to keep global temperatures within 1.5°C of pre-industrial levels by 2050.

Other Solution

Fuel and Engine Changes

Several approaches to reducing contrail warming have been proposed. Alternative fuels, such as Sustainable Aviation Fuels (SAFs) and hydrogen, could impact contrail formation. SAFs slightly increase engine exhaust water content and reduce soot, though the effect is uncertain, potentially reducing contrail warming by up to 81% or increasing it by up to 18%. Hydrogen would significantly increase exhaust water content and eliminate soot, potentially reducing contrail warming by up to 90% or increasing it by up to 60%. Additionally, engine modifications could potentially reduce particulate production.

Both fuel and engine changes face significant implementation challenges, typically requiring decades to scale up. However, the benefits of changing fuels could be achieved more rapidly by processing jet fuel to reduce its aromatic content.

Chapter 3

Systems Efficiency

2030 Goal 2: Systems Efficiency

Reducing fuel burn in aviation can be achieved through conventional measures such as new aircraft and engine technologies and improved operational efficiency. Based on a range of sources ^[2] Link to footnote ^[3] Link to footnote , the Aviation Impact Accelerator model predicts that these conventional measures can lead to up to a 22% reduction in fuel burn by 2050.

However, several bold efficiency measures exist which are currently hard to access because they involve system-wide change. If implemented, these measures could reduce fuel burn by up to 50% by 2050.

These measures include:

Accelerated Replacement: Increasing aircraft production to halve the fleet age.
Fly Slower: Reducing flight speed by around 15%, increasing transatlantic flight times by about 50 minutes.
Match Range: Ensuring more aircraft operate close to their design range by introducing new aircraft types and optimising purchasing and operating practices.

These bold measures are frequently overlooked because they require broad changes to the whole aviation sector, which are beyond the control of airlines. Therefore, policies must be implemented to drive the necessary system wide sector change needed to achieve a 50% reduction in fuel burn by 2050, returning aviation to 2019 emissions levels.

Governments and industry must collaborate to develop strategies that will enable the implementation of a new wave of policies to unlock these bold efficiency gains. Additionally, leading governments should immediately send clear market signals about their commitment to drive system-wide efficiency improvements.

An example of how bolder efficiency measures can be incentivised is the Corporate Average Fuel Economy (CAFE) standards that the US introduced for its automotive sector, which have reduced fuel burn by about 25% since 1975 ^[4] Link to footnote . Similar standards – many more ambitious - have been introduced in other locations such as the EU, Japan and China. To achieve similar results in aviation, governments could adopt a number of measures including: introducing Green Mandates for annual fuel burn reduction targets for the aviation industry; provide loan guarantees incentivising the purchase of more fuel-efficient aircraft; shifting accounting or taxation approaches to support accelerated turnover; mandates or incentives for aircraft scrappage; and more.

Outcome

The black line in the Outcome Figure below shows a business-as-usual scenario. This includes the introduction of a new generation of medium-range aircraft in 2035 and a new generation of the long-range aircraft in 2040, both featuring standard generational efficiency improvements. More details on the business-as-usual scenario are given in the Emission Baseline section.

The conventional measures, shown as the red region in the figure below, are projected to achieve an 11% to 22% reduction in emissions by 2050. The majority of this reduction comes from the introduction of 'leap technologies', which double the typical generational efficiency improvements to the aircraft launched in 2035 and 2040. Additional emissions reductions come from better air traffic control, decarbonising aircraft operations at airports, and increasing aircraft occupancy rates. A detailed breakdown of the conventional efficiency measured can be found in Key Fact 1 .

The addition of the bold measures to the conventional ones, shown as the green region in the figure below, is projected to achieve a cumulative 31% to 50% reduction in emissions by 2050. A detailed breakdown of the bold efficiency measures can also be found in Key Fact 1 .

The first bold measure involves accelerated fleet replacement, aiming to halve the aircraft retirement age from 30 to 15 years by 2050. This change alone could reduce fuel burn by 11% to 14%. Achieving this would require a notable increase in aircraft production over the next 30 years. Over this period, Airbus and Boeing are planning to double production, and either a further increase in their output by 50% or a third manufacturer joining the market would meet this need. While this might seem daunting given current aircraft delivery challenges, this increase in production can be strategically planned over 30 years. More details can be found in Key Fact 2 .

The second bold measure is to reduce flight speed by around 15% and design aircraft for these lower speeds ^[5] Link to footnote . This could reduce fuel burn by 5% to 7%. One drawback of reducing speed is the potential negative impact on airline productivity and passenger acceptance, especially for longer flights. However, for a transatlantic flight, the flight time would only increase by about 50 minutes, which could be offset by reduced airport waiting times.

The third bold measure is to better match aircraft design and operating ranges, ensuring more aircraft fly close to their design range. This could reduce fuel burn by 4% to 7% and can be achieved in three ways:

Incentivising airlines to prioritise matching design and operating range in their aircraft purchases and operations.
Introducing two new aircraft types, in addition to existing medium and long-range ones, with ranges of 2,000 km and 8,000 km into the market (the recent Airbus A321XLR, with an operating range of 8,700 km, is already ideal for one of these).
Dividing flights over 10,000 km into two segments where feasible ^[5] Link to footnote , thus lowering the design range of the aircraft for each leg. More details can be found on better matching aircraft design and operating ranges in Key Fact 3 .

For a fixed emissions reduction, the cost of implementing system efficiency improvements ( 2050 Ticket Cost ) is comparable to the cost of purchasing Sustainable Aviation Fuel (SAF) produced using Power-and-Biomass-to-Liquid (PBtL). System efficiency improvements reduce the volume of SAF required, thereby lowering the demand for biomass and renewable electricity. Consequently, prioritising systems efficiency is a cost-effective way to reduce global resource consumption.

Other Solution

Demand Management

Reducing aviation's environmental impact can also be achieved by managing demand, such as encouraging people to decrease travel or switch to alternative modes of transport. For instance, France has banned flights on routes with a rail alternative under 2.5 hours, cutting emissions by up to 95% per passenger kilometre, where a direct train is available. However, only about 7% of aviation fuel burn is regional, and only a small fraction can be replaced by rail.

Only about 10% of the world's population have ever flown ^[1] Link to footnote , but with the rising size of the middle classes in Asia, Africa, and South America, air travel is expected to double by 2050. This growth makes significant emission reductions through demand management challenging. Restricting emerging markets' access to air travel would be strongly resisted as these countries seek the same opportunities industrialised nations have long enjoyed. In industrialised countries, significant restrictions would need to focus on frequent fliers to gain public acceptance.

Chapter 4

Truly Sustainable and Scalable Fuel

2030 Goal 3: Truly Sustainable and Scalable Fuel

Globally, progress is being made in deploying Sustainable Aviation Fuels (SAFs) - synthetic kerosene fuels produced from renewable resources in production pathways that seek to cut the overall carbon footprint. Various bodies have set targets for their rollout. The UN’s International Civil Aviation Organisation aims for a 5% reduction in the carbon intensity of aviation fuels by 2030, while the European Union mandates a 6% SAF uptake by 2030.

One key resource for the production of such fuels is biomass – which provides the carbon critical for the development of the fuel. However multiple sectors draw on and are planning to draw on this resource, and producing it has implications for land use which is already highly pressured. There are real limitations to the scale of biomass that can be safely deployed across the economy and constraints on the sources.

Currently, SAF policies focus on reducing life cycle emissions within aviation and overlook the impact this biomass demand may have on emissions in other sectors. If left unaddressed, SAF production could lead to biomass consumption patterns that create significant emissions increases in other sectors, ultimately negating the benefits achieved within aviation. In turn, this would undermine the policy basis driving the rollout of SAFs and threaten the prospects for effectively scaling up. To rapidly scale SAF production within global biomass limits, aviation must take part in a cross-sector perspective, ensuring that biomass demand is understood and total emissions are minimised across all sectors.

Shifting to looking at SAFs through a cross-sector perspective offers the aviation industry an opportunity to demonstrate global leadership by developing a framework that encourages cross-sector coordination and best practices to minimise total cross-sector emissions. To achieve this, governments must immediately reform their Sustainable Aviation Fuel (SAF) policies to introduce a cross-sector approach, providing the industry with the certainty needed to invest. By 2030, governments and industry should implement a demonstration and deployment strategy that advances SAF production beyond biomass-based methods, incorporating more carbon-efficient synthetic production techniques. Additionally, policies must ensure that the aviation sector invests in low-carbon electricity and green hydrogen production to meet its own needs, preventing the diversion of limited low-carbon electricity and green hydrogen from other sectors.

Outcome

The figure below illustrates a scenario where 80% of global jet fuel is replaced with SAF by 2050. The red region represents the increase in total global emissions resulting from this scenario, including both emissions within aviation and those triggered in other sectors. Uncertainty is high, and in the worst cases, the emissions from other sectors could offset or even exceed the savings made in aviation. This uncertainty is based on modelling a wide range of scenarios, considering the transition of other sectors and the scale-up of biomass collection and low-carbon electricity.

The green region represents the case where Goal 3 has been effectively implemented, minimising emissions in other sectors. This scenario demonstrates that, if managed properly, emissions reductions of 50% to 70% are achievable by 2050.

Up until the early 2040s, the difference between the red and green regions will be primarily due to insufficient global biomass, with aviation taking priority over other sectors. After the 2040s, as more Power-to-Liquid fuels are employed, the difference also results from limited low-carbon electricity and green hydrogen production, with aviation taking priority over other sectors.

A major challenge in sustainably scaling up SAF production is the significant biomass requirement. Aviation's ability to outbid other sectors for biomass, given its small cost fraction in ticket prices , exacerbates this issue. By 2050, biomass costs are expected to account for only around 10% of the average ticket price if biofuels are used. Without regulation, SAF production could monopolise limited biomass resources, diverting them from other sectors and increasing their emissions.

Key Fact 1 shows that the maximum available global biomass, estimated by a range of international studies, is between 50 EJ and 160 EJ, considering only waste and currently collected biomass, with no land-use changes. While it’s impossible to estimate this sustainable limit with precision, it will likely evolve as our scientific understanding of global land use improves and agricultural advances are made. However, it is clear that there is a practical upper limit, and as easier-to-collect biomass is depleted, the harder-to-collect biomass will prove uneconomical and environmentally damaging. Today, the easiest biogenic feedstock available to produce SAF is waste biogenic fats, oils and greases, such as tallow and used cooking oil, typically converted in HEFA processes. However, the supply of these waste feedstocks is very limited and could only supply a small fraction (<5%) of 2050’s jet fuel demand. In many cases, demand for these feedstocks competes with other non-energy sectors such as cosmetics and pet food, and displacement of these feedstocks from these use cases would result in additional net virgin oils and fats production, usually eliminating the aviation sector emission benefit.

Key Fact 2 shows that the total global biomass required to decarbonise all sectors, including aviation, by 2050 is estimated to be between 80 EJ and 190 EJ. The lower estimates assume that all sectors, except for the hardest-to-decarbonise industries such as plastics, wood products, pulp, and paper, have ceased using biomass and that aviation fuel is produced using the most carbon-efficient method, Power-and-Biomass-to-Liquid (PBtL). The higher estimates assume that in addition to using biomass in the hardest-to-decarbonise industries, biomass is used to decarbonise heavy vehicles, around 15% of global electricity production, and about 15% of final building energy use, with aviation fuel produced through the less carbon-efficient Biomass-to-Liquid (BtL) method. It should be noted that even this higher estimate represents an extremely aggressive strategy for removing biomass from other sectors and will be extremely hard to achieve by 2050.

Comparing the global biomass requirement of 80 EJ to 190 EJ with the global biomass limit of 50 EJ to 160 EJ, it is clear that staying within the biomass limit will require all sectors that can transition away from biomass to do so, while those that cannot must then prioritise the most carbon-efficient methods of production.

Key Fact 3 shows that using Power-and-Biomass-to-Liquid (PBtL) is an effective way to lower the resource requirements of SAF in terms of both biomass and electricity use. It demonstrates that biomass usage is less than half of that required by Biomass-to-Liquid (BtL) and that low-carbon electricity consumption is less than half of what is needed for pure Power-to-Liquid fuels using Direct Air Capture (DAC).

While reducing the overall amount of low-carbon electricity used in fuel production is important, the more critical issue is that this electricity must be additional—specifically generated for the aviation sector. The required amount of low-carbon electricity is significant, with Power-and-Biomass-to-Liquid (PBtL) expected to consume 9-16% of the world's planned low-carbon grid by 2050, and Power-to-Liquid (PtL) requiring 23-41%. Ensuring that this power supply is additional is crucial, as displacing electricity from other sectors would result in continued reliance on fossil-based energy elsewhere, ultimately negating the emissions savings made in aviation.

Finally, it is important to note several other ways to minimise emissions. These are explained in more detail in Key Fact 4 . These include:

Resource-Efficient Production: Choose methods of fuel production like Power-and-Biomass-to-Liquid (PBtL) that make efficient use of biomass.
Integration of Carbon Removals: Incorporate carbon capture into bio-based SAF production to offset emissions.
Strategic Co-Location with Other Sectors: Combine SAF production with other sectors to collectively reduce emissions.

Other Solution

Offsetting Jet Fuel with Carbon Dioxide Removals (CDR)

Producing synthetic SAF is complex due to the processes needed to create long-chain hydrocarbons. This raises the question of whether it might be better to store carbon from biomass or CO₂ extracted directly from the air (using Direct Air Capture, DAC) underground while continuing to use fossil jet fuel. This method could be net zero or even carbon negative and could be significantly cheaper, costing around 50% to 75% of a Biomass-to-Liquid SAF.

However, this approach faces several challenges. Offsetting fossil emissions with carbon removals requires transparent auditing to ensure credibility and prevent double counting. Additionally, continued use of fossil jet fuel might be used to justify ongoing crude oil extraction. In the long term, as other sectors phase out crude oil, aviation could become isolated as one of the last users, facing major public acceptance issues and potentially rapidly rising costs.

It is therefore recommended that further work be conducted on the public acceptance, economic, technical, and policy challenges of offsetting jet fuel through Carbon Dioxide Removals (CDR).

Other Solution

Low Carbon Aviation Fuel

Emissions from current jet fuel can be reduced by approximately 17% through Low Carbon Aviation Fuel (LCAF), which lowers emissions associated with extracting and refining crude oil. As jet fuel represents approximately 5% of crude oil product, the impact of reducing upstream emissions driven by the use of LCAF could be around 20 times larger than the savings of the aviation sector.

Chapter 5

Moonshots

2030 Goal 4: Moonshots

The primary pathway to decarbonising aviation currently focuses on producing Sustainable Aviation Fuels (SAFs). However, the substantial resource requirements and complexity of fuel production present significant challenges and risks in realising this approach.

Relying solely on SAF could be avoided through the adoption of transformative technologies. In the automotive sector, for example, the shift to battery electric vehicles reduced both the planned and potential dependence on biofuels. Similar transformative technologies for aviation could include cryogenic hydrogen or methane fuels, hydrogen-electric propulsion, or synthetic biology to dramatically lower the energy demands of fuel production. Each of these technologies offers the potential to reduce aviation’s resource requirements and simplify fuel production compared to SAFs. By investing now in frontier technologies, governments have a once-in-a-generation opportunity to lead in transforming aviation, much like electric vehicles have reshaped the automotive industry.

However, for such an effort to achieve significant climate benefits by 2050, demonstration programmes must be launched immediately. These programmes should be designed to give real insight into the viability of new technologies by 2030, allowing the focus on and scale-up of the most viable transformative technologies shortly after. They must generate the experience needed to assess the scalability of these technologies and develop the expertise required for their deployment.

Several transformative technology demonstrators are discussed, but this chapter specifically focuses on cryogenic hydrogen and its potential contribution to emissions reduction by 2050. The AIA model indicates that targeting long-range flights first is critical for minimizing emissions by 2050. Long-range flights account for nearly half of the aviation sector’s emissions yet involve replacing only around 5,000 aircraft and converting approximately 50 of the world’s largest hub airports. Additionally, even with cryogenic tanks, the low weight of hydrogen, makes it an ideal fuel for long-range flights.

Three hydrogen demonstrator programmes are required:

The initial concept and technology development necessary to assess the potential of a long-range aircraft and engine development programme.
Conducting feasibility studies for transitioning hub airports to hydrogen.
Implementing technology feasibility and demonstration programmes for hydrogen liquefaction plants with outputs a hundredfold greater than today’s plants.

Delivering the three hydrogen demonstrator projects by 2030 will be extremely challenging, requiring focused effort from either an international coalition or a large country. However, the cost of these demonstrators is relatively small compared to other actions, such as scaling up SAF production.

The central point is that without launching and completing several focused demonstrator programmes by 2030, the aviation sector will be locked into relying on SAF for most of the emissions reductions in 2050 – exposing the sector to increased risks should there be challenges in delivering of SAF production.

Other transformative technologies will require different demonstrators, but the central principle remains the same: if these demonstrations prove successful by 2030, a significant reduction in emissions can be achieved by 2050. Conversely, a delay in demonstrations risks missing the opportunity to reach net-zero emissions by 2050 and delaying the crucial technological and business transformations needed.

Outcome

The red region in the figure illustrates the projected trajectory of hydrogen aviation, based on currently announced aircraft projects. Despite substantial progress in this field, hydrogen aviation is expected to contribute only 5% to 9% of emission reductions by 2050. In this scenario, hydrogen’s impact on aviation emissions would remain minimal until after 2060. This is mainly because the announced hydrogen-powered aircraft are for regional use, accounting for only a small share of global aviation fuel consumption. Additionally, it is important to note that no major aircraft manufacturer is currently considering hydrogen technology for the next generation of medium-range aircraft expected in the late 2030s.

The green region in the figure illustrates the projected trajectory for the case where the hydrogen moonshot demonstrators are successful, and a large-scale programme is launched in 2030. In this scenario, hydrogen aircraft will reduce emissions by 15% to 30% in 2050 and 30% to 70% in 2060.

The development and rollout program for hydrogen aircraft is shown in Key Fact 1 . It accounts for the time needed to conduct initial concept studies, develop the underlying technologies, complete the aircraft and engine development programmes leading up to the first flight, achieve entry into service, and ramp up production. Two timelines are considered: the slow one, which considers the current time scales in the aerospace industry, and the fast one, which considers historical projects which have been developed in times of strategic urgency. The analysis shows that a long-range hydrogen aircraft can enter into service between 2036 and 2042, followed by medium-range aircraft between 2042 and 2048. A new regional aircraft is also considered to enter the market in 2035.

Targeting long-range aviation first offers several advantages. Flights departing from around 50 of the world’s largest hub airports consume approximately half of aviation fuel. Focusing on long-range flights minimises the number of airports that need to transition. The leading airports would begin their transition in the mid-2030s and complete it by 2050. As medium-range aircraft are introduced by the mid-2040s, a number of medium-sized airports will also need to start transitioning five to ten years after the large airports. Initially, these airports are likely to rely on tanked liquid hydrogen before fully transitioning to new infrastructure.

The optimal solution for large hubs involves delivering hydrogen to hub airports via gas pipelines with on-site liquefaction, requiring hydrogen liquefaction plants about one hundred times larger than any existing facilities. For example, London Heathrow Airport ( Key Fact 2 ) would need 1.6 GW to power on-site hydrogen liquefaction, equivalent to a large UK power station, which could be supplied by a dedicated electrical grid connection or a hydrogen-power station. The scenario requires significant international coordination for airport transitions and the introduction of hydrogen aircraft into the current network.

As discussed in Key Fact 3 , hydrogen is ideal for long-range flight. This is because, even when accounting for the weight of the tanks, hydrogen fuel weighs only half as much as jet fuel. Notably, 45% of the take-off weight of the longest-range aircraft is fuel. Another advantage is that hydrogen is stored as cryogenic liquid, and the liquefaction process serves as an energy reserve. This can be harnessed during flight, reducing the overall energy required by about 10% to 15% compared to current aircraft.

Starting with long-range aircraft offers the advantage of maximizing emissions reductions while minimizing global infrastructure changes. However, this approach faces political challenges, as it requires multiple regions to transition simultaneously. An alternative, politically simpler solution is to focus on a single large region, such as the EU, and prioritise medium-haul aircraft first. While our model shows that this approach results in lower emissions reductions and increased infrastructure complexity, it could enable a more politically practical solution.

It should be noted that the ticket cost of hydrogen in 2050 is comparable to introducing biofuel ( 2050 Ticket Cost ) but is more affordable than fuels like Power-and-Biomass-to-Liquid.

Other Solution

To Mars and Back

Both SAF and hydrogen have significant disadvantages as aviation fuels. SAF is challenging to produce due to the complexity of manufacturing long-chain hydrocarbons, while hydrogen, though easy to produce, is difficult to implement in aircraft. Methane offers a potential solution. Its renewable production is simpler and less resource-intensive compared to SAFs, as it can be produced directly by anaerobic digestion of biomass or in one step from CO₂ and hydrogen via the Sabatier Process. Methane’s higher liquefaction temperature (-162°C) and greater volumetric energy density (58% of kerosene’s) compared to hydrogen (-253°C, 23%) simplify its implementation in aircraft.

The simplicity of producing methane is why it is considered for rockets to Mars, where it can be produced for the return journey. The existing gas infrastructure supports its distribution and allows for a gradual transition by mixing fossil and green methane. A potential issue is methane’s potency as a greenhouse gas, necessitating minimised leaks during production, transport, and flight, which is a manageable technical challenge.

Other Solution

Hydrogen-Electric Propulsion

Hydrogen-electric propulsion offers the potential for aircraft to have a very low climate impact. The low temperatures in fuel cells mean that nitrogen oxides (NO_x) does not form, and water vapour can be condensed out of the exhaust while flying through regions where contrails are formed. Additionally, electric propulsion enables the introduction of novel aircraft configurations, such as blown wings for reduced cruise fuel consumption, Short Take-Off and Landing (STOL), and Vertical Take-Off and Landing (VTOL).

Recent demonstrations, such as Joby and H2Fly’s 523-mile flight, highlight the rapid advancements in this technology. The AIA model shows that the range of hydrogen-electric aircraft is expected to increase from less than 1500 km today to over 4000 km by 2035 ^[6] Link to footnote . This would allow hydrogen-electric propulsion to compete with A320 and B737 in the medium-haul market, potentially replacing up to 50% of aviation’s fuel burn.

Other Solution

Synthetic Biology

Producing long-chain hydrocarbons using the Fischer-Tropsch process is resource-intensive and involves many conversion steps, resulting in low efficiency and high costs. This process relies on chain-elongation and chain-splitting techniques using thermochemical catalysts at high temperatures and pressures. These non-selective techniques lack the precision of biological enzymes, which can precisely stitch or cut hydrocarbon chains.

Synthetic biology offers a solution by designing organisms that convert common feedstock components, such as lignocellulose, CO₂, water, and energy from sunlight or electrons, directly into kerosene-like molecules in a single step. This approach could dramatically reduce the resources required to manufacture jet fuel.

Chapter 6

Practical Delivery of the 2030 Goals

The 2030 Goals are designed to drive substantial and systemic change in the aviation sector. History shows that crafting effective policies and strategies to achieve such a significant shift is incredibly challenging, often leading to imperfect outcomes and requiring multiple iterations. Therefore, it is crucial that decision-makers developing these policies and strategies can access the insights within the model simply and intuitively. This would enable them to experiment quickly and grasp the consequences of their actions.

A policy dashboard was developed for the Transatlantic Sustainable Aviation Workshop at MIT in April 2023 to support this need. This tool proved highly effective, enabling a collaborative team of UK, US, and EU policymakers to explore the complexities of the Aviation Impact Accelerator model and identify the most impactful leverage points within the system.

This section will show three future scenarios using a policy dashboard underpinned by the Aviation Impact Accelerator model. The first scenario shows the sector’s current trajectory where the 2030 Goals have not been enacted. The second and third scenarios show cases where different combinations of the 2030 Goals have been enacted, enabling net-zero aviation to be achieved by 2050.

As discussed in Goal 3, global biomass is limited, with estimates ranging between 50 EJ and 160 EJ. In these scenarios, we have assumed that the practical upper limit for biomass collection is 100 EJ, with aviation aiming to use a maximum of 30% of this total global biomass. While opinions will vary over whether these assumptions are correct, the authors believe they are reasonable.

It is important to note that many potential future scenarios are possible, but only three are shown here. The ones that have been chosen are simply to illustrate the importance of the 2030 Goals for achieving net zero by 2050 and do not represent the preference of the authors.

Scenario 1: Current Trajectory

In this scenario, ambitious targets and mandates for the scaled-up SAF production have been enacted and achieved. However, the four 2030 Goals have not been implemented. As shown below, this scenario fails to achieve net-zero aviation by 2050.

The dashboard indicates the market has scaled up the cheapest form of SAF but has a low level of success in mitigating the cross-sector impact of biomass and low-carbon electricity use. Consequently, aviation consumes more than the desired 30% of this total global biomass. The emissions caused in other sectors mean the uncertainty of the outcome is very high and dependent on the transition path of other sectors. In the worst case, the consequence of the scenario is to raise global emissions.

Additionally, in this scenario aircraft production has increased slightly faster than forecasts from Airbus and Boeing due to the entry of a third manufacturer into the market. This has reduced the retirement age of aircraft by 5 years. Contrail avoidance has been delayed while the focus has been placed on reducing scientific uncertainty.

Scenario 2: Net-Zero 2050 — Moonshots

In this scenario, the four 2030 Goals have been implemented, the Hydrogen Technology Demonstrator has proven successful, and the focus has shifted to scaling up long-range hydrogen aviation as quickly as possible. A key advantage of this approach is that, in the long term, it eliminates the need for biomass. Operation Blue Skies has also been successful, with a global contrail avoidance scheme beginning to scale up from 2030. This scenario achieves net-zero aviation by 2050.

To reach net zero by 2050, the dashboard indicates that additional policies must be implemented. These include increasing aircraft production rates to 50% above current forecasts by 2050, which would halve the average fleet age. This accelerates the introduction of hydrogen-powered aircraft, leading to hydrogen being responsible for a 40% reduction in emissions by 2050. As hydrogen technology is adopted, the aviation sector's reliance on Sustainable Aviation Fuels (SAFs) decreases, allowing simpler Biomass-to-Liquid (BtL) plants to meet demand. Consequently, aviation's biomass consumption remains below the target of 30% of global biomass and begins to decline after 2050. Moreover, this scenario eliminates the need for efficiency measures such as flying slower or tailoring aircraft design to specific flight ranges.

Scenario 3: Net-Zero 2050 — Truly Sustainable and Scalable Fuel

In this scenario, the four 2030 Goals are implemented, but the result of the Moonshot Demonstrators is that no transformative technology is viable on the necessary timescales. As a result, the pressure on biomass becomes extremely high and must be managed through bold efficiency measures and strong biomass policies. Operation Blue Skies has been successful, with a global contrail avoidance scheme beginning to scale up from 2030. This scenario achieves net-zero aviation by 2050.

The dashboard indicates that the primary challenge is limiting biomass usage to 30% of global biomass. To achieve this, policies must drive the most aggressive efficiency measures, reducing the demand for SAF by 31% to 50% by 2050. These measures include halving the average fleet age, designing aircraft to fly 15% slower, and ensuring that more aircraft operate closer to their design range. The dashboard also highlights the urgent need to rapidly scale up Power-and-Biomass-to-Liquid (PBtL) production starting in the late 2030s, which acts to hold aviation biomass use to the desired level. PBtL plants would need to produce roughly half of the required SAF by 2050.

It is important to note that this scenario heavily relies on successfully scaling up global biomass in an economically and ecologically sustainable manner, leaving the aviation sector vulnerable to external factors beyond its control. In such cases, dashboards powered by models like the Aviation Impact Accelerator are incredibly useful, as they enable the development of policies that are more resilient to known uncertainties and allow for rapid adjustments as new information becomes available.

Chapter 7

Conclusion

It is crucial to recognise that most existing aviation net-zero pathways mistakenly assume a smooth transition to net zero, with multiple technologies coexisting beyond 2050. History shows that technological transitions are rarely smooth; competing technologies typically vie for dominance until one prevails and displaces the others. This misperception of a smooth transition is harmful, as it creates the illusion that delaying action will result in only a minor increase in emissions by 2050. The findings of this report, supported by the Aviation Impact Accelerator (AIA) model, clearly demonstrate that this assumption is flawed. Without bold intervention today, the opportunity to transform the aviation industry will be lost.

This report outlines an ambitious five-year plan to set the aviation sector on a path to achieving net zero by 2050. It establishes four key Sustainable Aviation Goals for 2030, each targeting critical leverage points. If these goals are not immediately implemented and achieved by 2030, the window for transformation will close, leaving the world to face the escalating climate consequences of a rapidly expanding aviation industry, which is projected to at least double by 2050. The urgency of this moment cannot be overstated.

Footnotes

Gössling, S., & Humpe, A. (2020). The global scale, distribution and growth of aviation: Implications for climate change. Global Environmental Change, 65, 102194
International Civil Aviation Organization (ICAO). (2022). Appendix M4: Additional information on LTAG analysis. In LTAG Report
Jensen, L. L., Bonnefoy, P. A., Hileman, J. I., & Fitzgerald, J. T. (2023). The carbon dioxide challenge facing U.S. aviation and paths to achieve net zero emissions by 2050. Progress in Aerospace Sciences, 141, 100921
U.S. Department of Transportation. (2022, April 1). USDOT announces new vehicle fuel economy standards for model year 2024-2026 .
Yutko, Brian M. (2014) The impact of aircraft design reference mission on fuel efficiency in the air transportation system [Doctoral dissertation, Massachusetts Institute of Technology]. MIT Research Repository
World Economic Forum. (2022, July). Target True Zero: Unlocking Sustainable Battery and Hydrogen-Powered Flight

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Authors

Robert Miller, Eliot Whittington, Samuel Gabra, Paul Hodgson, Jay Green, Jia Wei Kho, Jessie Smith, and Deepanshu Singh.

Partners

We would like to thank our partners for supporting and funding the AIA. Without their support this report would not have been possible: 4AIR, Boeing, Emirates, Flexjet, Quadrature Climate Foundation, Reviate at Breakthrough Energy, Rolls-Royce, Stratos, the Sustainable Markets Initiative, the Royal Air Force, UK Department for Energy Security and Net Zero, and UK Department for Transport.

Transatlantic Sustainable Aviation Partnership

The organisations who attended the inaugural meeting of the Transatlantic Sustainable Aviation Partnership at the Massachusetts Institute of Technology (MIT) in April 2023, hosted jointly by the University of Cambridge and MIT, where the original concepts for the four Goals were conceived included: Aerospace Technology Institute (ATI), EU Clean Aviation, Massachusetts Institute of Technology (MIT) Laboratory for Aviation and the Environment, National Aeronautics and Space Administration (NASA), Penn State University, UK Department for Business & Trade (DBT), UK Department for Transport (DfT), University College London (UCL), Air Transport Systems Lab, University of California San Diego, University of Cambridge Aviation Impact Accelerator, USA Federal Aviation Administration (FAA), and Washington State University.

It should be noted that the views published in this report are those of the Aviation Impact Accelerator and do not represent the specific views of those attending the workshop.

Acknowledgements

We would like to acknowledge the contributions of the following people to the report, the underlying model, and the Transatlantic Sustainable Aviation workshop and roundtable: Mansoor Abulhoul, Omer Aiuby, Caleb Akhtar Martinez, Florian Allroggen, Jill Ashcroft-Campion, Beth Barker, Nils Barner, Steven Barrett, Killian Bartsch, Phoebe Bendall, Peter Bennett, Mark Bentall, JoeBen Bevirt, Dirsha Bohra, Paul Bond, Samuel Brockie, Jean-Francois Brouckaert, Lucy Bruzzone, Ghenadie Bulat, Freya Burton, Johnston Busingye, King Charles III, Nathan Clark, Richard Clarkson, Polly Courtice, James de Salis Young, John Dennis, Haldane Dodd, Nicole Didyk Wells, Sebastian Eastham, Liz Edwards, Jenifer Elmslie, Gary Fitzgerald, Lara Fowler, Henry Free, George Freeman, Steve Freeman, Gene Gebolys, Maja Glavin, Jordi Gomez-Alberti, Jon Gordon, Matthew Gorman, Holly Greig, Ewan Gribbin, Paul Griffiths, John Hansman, Shaun Harris, Eric Hendricks, James Hileman, Malcolm Hillel, Ian Henderson, Gim Huay Neo, Eisaku Ito, Shaun Ho, John Holland-Kaye, Lindsay Hooper, Jerome Jarrett, Jennifer Jordan-Saifi, Julia King, Richard Knighton, Axel Krein, Joyce Light, Prem Lobo, Lorraine Lorimer, Nateri Madavan, Angela McLean, Anmol Manohar, Charalampos Michalakakis, Matteo Mirolo, Alan Mitchell, Paul Monks, David Morgan, Adam Morton, Herve Morvan, Abby Munson, Massimiliano Nardini, Andy Neely, Anna Oldani, Anil Padhra, Ralph Percival, Oriel Petry, Annie Petsonk, Ben Petty, David Pitchforth, Prakash Prashanth, Deborah Prentice, Matt Prescott, Tony Purnell, Miruna Rapeanu, David Reiner, Kennedy Ricci, Alex Routh, Richard Sandberg, Dinesh Sanekommu, Andreas Schafer, Marc Shapiro, Grant Shapps, Vidhi Sharma, Sarah Sharples, Raymond Speth, Noli Shelala, James Stephens, Marc Stettler, Andrew Sweeney, Jack Swerdlow, Katharina Tegethoff, Neil Titchener, Nigel Topping, Mark Turner, Adam Twidell, Patrick Vallance, Maria Vera-Morales, David Victor, Grazia Vittadini, Edgar Waggoner, Richard Wahls, Ian Waitz, Kevin Welsh, Andrew Wheeler, Michael Wolcott, Tom Yorke, and Brian Yutko.

Citing this report

Aviation Impact Accelerator, 2024. Five Years to Chart a New Future for Aviation: The 2030 Sustainable Aviation Goals [R.J. Miller, E.N. Whittington, S. Gabra, P.J. Hodgson, J. Green, J. Kho, J.R. Smith, D. Singh]. AIA, University of Cambridge.

About

The Aviation Impact Accelerator

The Aviation Impact Accelerator (AIA) is a global initiative jointly led by the University of Cambridge’s Whittle Laboratory and Institute for Sustainability Leadership (CISL), bringing together experts from across the sector and beyond to accelerate the transition to climate-neutral aviation. Our mission is to develop evidence-based tools and insights to allow decision makers to map, understand and embark on the pathways towards sustainable flight.

The Whittle Laboratory

The Whittle Laboratory at the University of Cambridge is one of the world’s leading laboratories working on reducing the climate impact of aviation and power generation. The Lab has partnered with industries such as Rolls-Royce, Mitsubishi Heavy Industries, Siemens and Boeing for over 50 years successfully translated hundreds of primary research ideas into industrial products. Its research has been awarded the American Society of Mechanical Engineers highest honour, the ‘Gas Turbine Award’ 15 times, more than any other institution or company. In 2026, the New Whittle Laboratory will open, housing the Bennett Innovation Laboratory and the UK National Centre for Propulsion and Power.

The University of Cambridge Institute for Sustainability Leadership

CISL is an impact-led institute within the University of Cambridge that activates leadership globally to transform economies for people, nature and climate. Through its global network and hubs in Cambridge, Cape Town and Brussels, CISL works with leaders and innovators across business, finance and government to accelerate action for a sustainable future. Trusted since 1988 for its rigour and pioneering commitment to learning and collaboration, the Institute creates safe spaces to challenge and support those with the power to act.

Contact Us

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Disclaimer

This document is published by the Aviation Impact Accelerator, an initiative led by the University of Cambridge. The Aviation Impact Accelerator aims to collect evidence and knowledge by engaging a wide range of stakeholders. The findings and conclusions expressed within do not necessarily represent the views of the University of Cambridge, nor those of the Aviation Impact Accelerator’s partners, funders, and collaborators.

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