What the aviation industry tells you and what they DON’T tell you

What we need to know about decarbonisation promises and false solutions

Following the Covid19-Pandemic and the halt it put to most national and international flights, the aviation industry and their lobby are working hard to get back to their pre-COVID climate damaging growth path. As a reaction to the rising public and political awareness of the climate harming effects of aviation, the industry accompanies its quests for bailouts and further subsidies with promises of green flying through technology.

By taking a closer look at what the industry tells us and what they don’t tell us, in our new fact sheet series we debunk common misconceptions and look behind the green curtain of their promises

  • Efficiency
  • Electric Flight
  • Hydrogen
  • Biofuels
  • E-fuels
  • Net Zero

Efficiency Improvements

Aircraft efficiency refers to the amount of fuel burned (and emissions produced) by an aircraft in order to transport its payload (passengers or cargo) a given distance (e.g. one kilometer). Efficiency improvements (i.e. reductions in fuel burn) are achieved by optimising the design of the aircraft, the engines, the airline operations (e.g. the flightpath) and by increasing the amount of passengers/cargo carried onboard the aircraft.
CO2/passenger-km is proportional to efficiency (fuel/pass-enger-km).

Flying can be decarbonised by improving aircraft efficiency. History shows us that “efficiency improvements” have always been accompanied by increased emissions! This is because efficiency improvements also reduce the cost of
flying and contribute to air traffic growth, leading to emissions growth which far outpaces the emissions reductions
of efficiency gains.
Supporting aircraft technology development and air traffic optimisation will have a beneficial environmental impact. Emissions reductions through efficiency gains can also be cancelled out by airlines upgrading the class of seats, and by flying further or faster.
Therefore: financial restrictions on airlines such as increased
pricing or fuel taxes shouldn’t be imposed, as this will reduce profit available to invest in new technologies and processes.
Therefore: we need further measures to limit emissions such as increased pricing or fuel taxes to incentivise less fuel burned. Such policies will actually accelerate efficiency improvements.


Efficiency does not “decarbonise” aviation

A common industry misconception is that flying can be decarbonised by making aircraft more efficient every year, often expressed in misleading statements such as: “since the advent of jet technology, carbon-dioxide emissions from aviation have reduced by 80%”.1

It’s correct that these improvements have resulted in emissions reductions per passenger-km flown. Coupled with tax breaks and subsidies, and increasing purchasing power of the global population, this has resulted in a rapid growth of air traffic (doubling every 15 years) and of CO2 emissions that has far outstripped the efficiency savings. [see infographic]

As aircraft efficiency improves, some airlines simultaneously reduce their per seat efficiency by increasing the number of more profitable business or first class seats. They also fly further (ultra long-haul) which burns more fuel, even in efficient aircraft. A new generation of supersonic aircraft are also being developed2 that would require up to nine times more energy per passenger-km than subsonic aircraft.3 Private/business jet use has also been increasing; they are 5-14 times more polluting than commercial aircraft due to low passenger density or higher flight speeds.4

Prior to the COVID-19 pandemic, Airbus had projected that air traffic would double again by the mid-2030s and then again by 2050. This would amount to an 8-times increase from year 2000 levels,5 i.e. an average growth of 4.2% per year. Despite the slump in air traffic due to COVID-19, the industry still predicts growth rates of about 4% per year beyond 2024 until 2038.6

The earth’s atmosphere isn’t affected by emissions per passenger-km, but instead by total emissions produced. This has been rapidly increasing, rather than decreasing.

In a poorly-regulated industry, efficiency improvements may facilitate market growth and increase total emissions, not reduce them. This is known as Jevon’s Paradox.7 Thus, efficiency gains alone cannot be relied upon to decarbonise the industry – we also need regulations to limit air traffic.

A method of limiting aviation emissions would be to increase the cost of jet fuel in order to incentivise reduced consumption. Additionally, a frequent flyer levy or air miles levy could incentivise people to fly less.8 There are historic examples of jet fuel price increases: e.g. the OPEC oil crisis in the 1970s-80s, during which it was seen that aircraft technology development actually accelerated, as there was a larger incentive to reduce fuel burn (e.g. flight testing of “Open Rotor” concepts). These designs were shelved when the oil price decreased again in the 1990s and are yet to re-emerge due to low fuel prices.9 This example demonstrates that reality does not match the narrative presented to us by airlines and the aviation industry.10 Financial restrictions on airlines such as increased pricing or fuel taxes wouldn’t reduce spending on new technologies and processes as claimed by airlines11; rather, they would increase the industry’s desire to chase greater efficiency improvements.

End Notes & Literature

1 The Engineer (2019):
2 BBC (2021):
3 Kharina, A et al. (2018):
4 Murphy, A et al. (2021):
5 Airbus (2019):
6 ATAG (2020):
7 Wikipedia:
8 Stay Grounded (2018):
9 Wikipedia (2021):
10 Further reading: Peeters, P et al. (2016):
11 Flightglobal (2020):

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Electric Flight
Electric aircraft propulsion systems typically involve aircraft propulsors (propellor or fan blades) that are driven by electric motors. In “fully-electric” aircraft, these motors are powered by electrical energy provided directly from batteries or hydrogen fuel cells (see Fact Sheet 3). In “hybrid-electric” aircraft, these electric motors act in series, or parallel, with a combustion engine powered by jet fuel.
Electric aircraft will be “zero emissions”. Electric aircraft will NOT be “zero emissions”
until the electric grid is fully decarbonised.
Electric flight is an efficient mode of transport. Electric flight is NOT efficient compared to public transport on the ground (rail, coach)
Their contribution to decarbonising aviation
will be significant.
Any contribution to decarbonising aviation will be severely limited by range and payload.
They will be available soon. The only aircraft likely to be certified this decade will be very small and we won’t see larger aircraft before 2050, too late to prevent climate breakdown.

Electric aircraft will NOT be “zero emissions” any time soon

“Fully-electric” aircraft are powered by batteries, and if the batteries are charged using only renewable electricity, the aircraft operation can be considered “zero emissions”. However, we are a long-way from decarbonising electricity generation, and adding additional load from other energy-intensive activities, will make it harder to move away from fossil fuels. Also, manufacturing the vehicles and batteries has significant social and environmental impacts, due to mining the necessary materials such as lithium and cobalt and producing the components. As such, even “fully-electric” aircraft cannot yet be considered “zero emissions”.

“Hybrid-electric” aircraft burn jet fuel, and so still produce CO2 and other greenhouse gas emissions during operation. They are therefore not “zero emissions”. These hybrid-electric systems unlock potential new aircraft and engine architectures, such as “distributed propulsion” which could provide aircraft-level aerodynamic improvements, although such improvements can often be negated by the additional complexity of designs.

Electric flight is NOT efficient

Flying is a fundamentally inefficient mode of transport and difficult to electrify. It should not be favoured over more efficient ground transport options that are easier to electrify. This is because aircraft use large amounts of power to take-off and climb and are more sensitive to the weight of batteries and electrical systems1. Where infrastructure allows: lower energy- and emissions- intensive ground-based public transport options such as rail, coach, or ferry services should be favoured at the short distances where electric aircraft are viable.

There are a large number of relatively small start-up companies attempting to develop and certify electric aircraft over the next decade. Many of the concepts receiving early investment are electric Vertical Take-Off & Landing (eVTOL) aircraft2. These aircraft are designed to take-off and land on helicopter pads or short runways, in order to enable versatility of operation from a range of locations. However, these aircraft are even more inefficient than conventional fixed-wing electric aircraft, as they have higher take-off and landing power requirements and higher weight and drag during the rest of the flight. They should not be considered a positive environmental development.

Decarbonisation will be severely limited by aircraft range and payload

Current batteries and electrical systems are far too heavy to displace most jet fuel and combustion engines.

The Chief Technology Officer of Airbus has stated that “even assuming huge advances in battery technology, with batteries that are 30 times more efficient and ‘energy-dense’ than they are today, it would only be possible to fly an A320 airliner for a fifth of its range with just half of its payload”3. It is therefore not foreseeable that this type of aircraft which is the most common in airports for short-haul flights could become electric in the short or even medium term. Only very small, short-range aircraft will be electric. This is reflected by the fact that most companies attempting to certify electric aircraft during the 2020s are developing aircraft carrying less than 10 passengers which do not fit the current configuration of most airports. In addition, unlike a fuel tank where the weight decreases as fuel is burned during the flight, a battery does not become lighter during the trip. These issues further impact the payload and range capability of the aircraft4.

Currently this means that electric aircraft will only be viable for short flights under 1,000 km by 2050 which account for only 17% of aviation CO2 emissions5. However, the scope to decarbonise overall aviation emissions is even more limited because, although electric aircraft can be justified for some niche cases in regions where ground transport options are poor, everywhere else short flights can be substituted by more efficient train, coach or ferry services.

Large electric aircraft won’t be here soon

Improvements in the weight of battery technology will not overcome their disadvantages any time soon. The Chief Technology Officer of United Technologies declares:
“Unless there is some radical, yet-to-be invented paradigm shift in energy storage, we are going to rely on hydrocarbon fuels for the foreseeable future”6. In its recent “Net Zero by 2050” report7, the International Energy Agency (IEA) sees the adoption of commercial battery electric and hydrogen aircraft from 2035, but expects that these aircraft would account for less than 2% of global aviation energy consumption in 2050. Hence, we should not allow the talk of electric flight to distract us from the priority of reducing aviation emissions today.

End Notes & Literature

1 GreenBiz (2018):
2 FlightGlobal (2021):
3 BBC (2019):
4 Airbus (2019):
5 CleanSky2&FCH (2020):
6 BBC (2019):
7 IEA (2021):, p.136

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Hydrogen Flight
There are plans to use hydrogen as a power source for aircraft instead of kerosene. It could either be burned in a jet engine or used to feed a fuel cell to generate electricity to power a propeller. It is produced from other energy sources, has a significant energy loss during the process and is usually stored in liquid form at −253 °C.
Happening soon
New aircraft propelled by hydrogen could enter into service by 2035.
Too late
If it happens, it will come much too late to tackle the climate
Zero emissions
When burned or used in a fuel cell, hydrogen does not produce any CO2, only water.
Not for medium and long-haul flights
Hydrogen will not be viable for medium and long-haul flights before 2050. Until then, only the regional and short-haul market should be targeted, a large part of which can be substituted by road or rail.
Government support required
Public money is needed for funding for hydrogen aircraft development and to subsidise hydrogen production.
Not zero emissions
Hydrogen-powered aircraft will not have zero emissions, even if hydrogen is produced from renewable electricity, because it will still emit NOx and generate contrail cirrus that have a higher climate impact than CO2 today.
Huge energy consumption
The deployment of “green” hydrogen in aviation would require huge quantities of renewable electricity, which would deprive other sectors needing to decarbonise.
Success not assured
Hydrogen-powered aircraft exist only on paper. Before it becomes a reality, many problems must be solved, especially in the field of safety, and new technologies must be developed.
Financial support from governments means taxpayers pay
…most of whom never fly.
Airbus studied hydrogen aircraft in the 2000s but shelved their plans in 2010 due to technical issues1 that are yet to be resolved. In 2020, they then announced their intention to restart development of new hydrogen aircraft that could enter into service in 2035. They are studying four concept aircraft and will select one by 20252,3. Other manufacturers are also developing small hydrogen aircraft that may be certified in the 2020s.

Hydrogen aircraft unable to meet climate targets in time and quantity

Even if the aggressive schedule announced by Airbus in 2020 is met, it will be too late for the climate. According to the United Nations Environment Program (UNEP), worldwide GHG emissions must be reduced by 55% by 2030 and 90% by 2050 in order to not exceed the globally agreed 1.5°C heating limit4. The design of a whole range of aircraft and the conversion of the fleet to hydrogen would start too late and take too long to meet this goal. Aircraft have a typical lifetime of 25 years.

According to a report produced by the European Commission (EC) in collaboration with key industry partners, hydrogen would be best suited for regional and short- to medium-haul flights. For long-haul flights, which contribute about one third of aviation emissions, hydrogen would not economically compete with synthetic fuels before 20505. By then, for that segment, the industry plans to rely upon alternative jet fuels (biofuels and e-fuels – see Fact Sheets 4 and 5). More recently, Airbus stated that a medium-haul aircraft would not be available before 2050, so, before that time hydrogen could potentially displace less than 20% of CO2 emissions6.

Hydrogen would still have significant non-CO2 impacts

The EC report takes into account the CO2 as well as the non-CO2 impact of aviation on climate, NOx, water vapour and contrails, considering that the total impact is 3.1 times that of CO2 alone (see also Fact Sheet on non-CO2)7. It estimates that the total climate impact could be reduced by only 50-75% versus kerosene if hydrogen is burned in turbines and 75-90% if it is used in fuel cells. But this is still highly hypothetical.

Producing green hydrogen would require huge renewable electricity resources

Hydrogen aircraft are part of a new economy of hydrogen aiming at replacing fossil fuels where electricity is not a possible alternative.
In order to be “carbon-free”, hydrogen needs to be produced with renewable electricity (green hydrogen > see infobox).

The challenge is that the energy requirements are huge and will exceed production capacities needed to:

  • Replace coal and gas in power plants that supply the electric grid
  • Help satisfy new demand for electricity (cars, heating, data, etc.)
  • Replace today’s grey hydrogen (produced from fossil fuels) used for industrial processes (e.g. fertiliser production)
  • Satisfy new demand for hydrogen for trucks, ships…
  • Satisfy new demand for hydrogen for production ofe-fuels for aviation

In a scenario where 40% of the airline fleet would be converted to liquid hydrogen in 2050 and the rest of the fleet would use e-fuels, the resulting electricity demand would be equal to the current total worldwide electricity production and about four times the production of renewable electricity in 20188. As demand for electricity grows so does the risk that renewable electricity supply will not be able to match it, which will increase the risk of using non-renewable power.

Financial support from governments is unjustified: the polluter should pay

Airbus says “support from governments will be key to meet their ambitious objectives with increased funding for research and technology, digitalisation and mechanisms that encourage the use of sustainable fuels and accelerate the renewal of aircraft fleets”9.

However: given that most taxpayers rarely or never fly10 it would be unfair for them to subsidise research and development, particularly as the commercial success of hydrogen is uncertain; timescales are lengthy; and any significant deployment of hydrogen aircraft would be a waste of limited renewable energy resources.

Grey, Blue and Green Hydrogen

This colour code refers to different production methods:

  • Grey Hydrogen = produced from methane or coal (both fossil fuels)
  • Blue Hydrogen = Grey Hydrogen combined with Carbon Capture & Storage (CCS)
  • Green Hydrogen = produced (via electrolysis) from water via renewable electricity

In 2018, the vast majority of the hydrogen production was “grey”, accounting for 2% of total global CO2 emissions. Only 0.5% of the production was “green”, and a tiny amount was “blue”11. “Blue” hydrogen is unproven at scale, and ultimately still involves the use of fossil fuel and may produce more carbon emissions than simply using “grey” hydrogen12.

Today, hydrogen is mostly used by industry, for oil refining and for producing ammonia fertilisers. But many sectors, including aviation, are exploring its potential to support clean energy transitions and a new hydrogen economy is being projected.

As new uses for hydrogen develop, there is a major concern that the oil and gas sector will continue with business as usual in order to fulfill new hydrogen demand by extracting it from fossil hydrocarbons, rather than leaving it in the ground.

Success is far from assured

Hydrogen flight is unproven, with many technical and safety aspects yet to be understood. There is some skepticism even within the aviation industry. Boeing is not following Airbus13 and engine manufacturers have expressed reservations14. Even Airbus have admitted that hydrogen will not be widely used in planes before 2050, stating that only regional 50-100 seaters would be ready for hydrogen in the 2030s, a small market with a small share of current CO2 emissions15. If airlines transition to using a large amount of such aircraft, this will substantially affect their operations and the design of airport infrastructure (e.g. runways, gates, terminals, fuelling and maintenance requirements). It would therefore be sensible to halt aviation expansion plans until we know to what extent hydrogen aircraft will be used.

End Notes & Literature

1 BBC News (2010):
2 Airbus (2020):
3 Airbus (2020):
4 UNEP (2019):, p. 15
5 CleanSky2&FCH (2020):
6 Reuters (2021):
7 Stay Grounded (2020):
8 CleanSky2&FCH (2020):
9 Airbus (2020):
10 Gössling, S. et al. (2020):
11 IEA (2021):
12 Howarth, R. et al (2021):
13 Simple flying (2021):
14 France TV (2020):
15 Reuters (2021):

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Alternative jet fuels or so-called “Sustainable Aviation Fuels” (SAF) are liquid hydrocarbon fuels that can be used with existing aircraft in place of kerosene produced from fossil fuels. The industry’s premise of the sustainability of these fuels is to create the fuel using CO2 taken from the atmosphere, rather than using fossil fuels extracted from deep underground that will then emit additional CO2 to the atmosphere when burned. The argument is that blending these fuels with fossil fuels would thereby reduce emissions.

Alternative jet fuel can be broadly categorised into two varieties:

  • Biofuels – produced from biomass sources (explained below)
  • Synthetic electro-fuels (e-fuels) – produced using elec-tricity (see Fact Sheet 5)

Biofuel production can use various sources of biomass as an input. First generation biofuels use agricultural crops. Second generation biofuels aspire to use industrial, agricultural, municipal or household waste, such as: used cooking oil, fat, corn husks, forest resources, or food waste.

Aviation will not use first generation biofuels from crops but will instead use second generation biofuels from “sustainable waste” that will not compete with agriculture or cause adverse environmental or social impacts.

Aviation biofuels could significantly reduce emissions vs. fossil jet fuel.

Aviation biofuels could be scaled up rapidly to a significant percentage of jet fuel consumption.

Due to the significant extra cost, governments should provide financial support for biofuels, so that aviation industry growth is not affected.

Aviation does not rule out the use of first generation biofuels from crops, which are proven to cause very serious environmental and social impacts such as biodiversity loss, rising food prices and water scarcity.
There is a very limited quantity of “sustainable waste” available globally for second generation biofuels. This could also be used more efficiently to decarbonise other sectors.


Biofuel use can still produce significant CO2 emissions. Also non-CO2 emissions which have a strong climate impact today, will only be partially eliminated by using biofuels.

Aviation biofuel scale up has been promised by the industry for more than a decade but currently less than 0.01% of jet fuel is biofuel. Second generation biofuels are likely to only replace a small percentage of fossil fuel use in the future.

Subsidies for biofuels risk wasting public money on a false solution. They would keep flying artificially cheap which would result in more air traffic and emissions than if the industry paid.


Biofuel use is severely constrained by the sustainability and availability of biomass

It is often claimed that aviation would use only second generation biofuels derived from “waste” sources, therefore avoiding any direct or indirect sustainability impacts. Yet the use of first generation biofuels from crops and even entire trees has not been ruled out. There are plans for huge “SAF” refineries in Paraguay using soybeans as a feedstock1 and such fuels are permitted under the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), which is the only internationally agreed policy and runs until 20352. The threat of scaling up the use of commodities like soy or palm oil with high risk of deforestation is increasing as greater political emphasis is placed on the supposed benefits of “SAF”.

The cultivation of energy crops in large monoculture fields increases the use of fertilisers, pesticides and herbicides; with devastating environmental, biodiversity and health impacts. The expansion of agriculture like soy and palm leads to CO2 emissions from land use change which can be similar to, or greater, than fossil fuel emissions3 (Fig. 1) It can also result in humanitarian impacts4 like land conflicts, labour abuses, rising food prices, water scarcity and chronic disease in neighbouring communities from pollution.

The only process currently able to produce second generation biofuels for aviation at a commercial scale uses “waste oils”, due to its similarity to biodiesel, which is already produced at a limited commercial scale for the road sector. It has been found that when “waste oils” are used to produce large quantities of biodiesel, it displaces their use in other sectors; which then transition to other sources, such as palm oil5. This also creates the opportunity for fraud, for example: where fresh palm oil has been sold as “used cooking oil”6. Also palm oil or palm oil derivatives are often being used but being disguised by another term.7 This indirectly causes an increase in crops for energy with their associated impacts.

Biofuels would compete with other applications

The future quantity of any sustainable biomass “waste” available globally is strictly limited and without fuel production processes having been demonstrated at any significant commercial level. An EU report (contributed to by Airbus, Boeing, BP, Shell, and easyJet) in 2020 stated that “biofuels’ reliance on feedstock, changes in land use, high water use, and/or monoculture (i.e., the production of a single crop) means that the aviation industry will be competing with other interests that need the feedstock for other purposes”8.

Governments will need to use any biomass produced to feed a growing global population whilst also decarbonising the power, heating, agriculture (e.g. replacing fossil fuel fertilisers) and transport sectors. Current government policies will not result in combustion engines being completely phased out of cars, trucks, or ships until after 2040. This means aviation will compete with ground transport for limited quantities of sustainable biofuel over the next few decades and it is recognised that high targets for aviation biofuels may only incentivise the diversion of resources from existing use in the road sector9. The UK Government notes that when production facilities produce more aviation biofuel than road biodiesel, their overall efficiency decreases and production costs increase; making “economy-wide decarbonisation more expensive”10. Therefore, the only result would be to shift an emissions saving from one sector to another, whilst decreasing the total emissions saving achieved and increasing costs. There are also dangerous plans to rely heavily on biomass for negative emissions via Bioenergy Carbon Capture & Storage (BECCS) facilities, which is an unproven technology and would increase pressure on scarce global resources and amplify the risk of all the impacts detailed above.

Biofuels would only partially reduce aviation climate impact vs. fossil fuel

The industry claims that “SAF can reduce emissions by up to 80% during its full life cycle”11. However, GHG savings of only 60% have been proposed at national levels as a threshold for “SAF”12 and fuels eligible under the international CORSIA scheme can have savings as low as 10%.13 In addition, aviation also produces non-CO2 emissions such as contrails which are estimated to cause a greater global warming effect than aviation CO214. Recent studies have shown that while biofuels can contribute to reducing non-CO2 emissions, they will only be partially reduced15. So even if fossil fuel were entirely replaced by biofuels, significant emissions would still be generated.

Governments should not subsidise aviation biofuels: the polluter should pay

Even if scaled up further, aviation biofuels will still cost far more than kerosene. Biofuel from “waste oil” is the most cost competitive but still costs double the price and “other conversion processes cost as much as eight times the price”16. These increased costs would undermine the expansion plans of the industry. The only way the aviation industry can continue to grow whilst using larger quantities of alternative jet fuels such as biofuel, would be to obtain large government subsidies for their production. According to a 2019 study by the International Civil Aviation Organisation (ICAO), 328 new large bio-refineries would need to be built every year by 2035, at an approximate capital cost of US$29-115 billion a year to generate enough biofuel for international aviation only17. However, investing in bio-refineries would pose a huge risk to public finances as it is unlikely, for the reasons given here, that aviation biofuels can ever be viewed as “sustainable”. This would result in facilities that are likely to turn into “stranded assets” with a large loss of investment. In the end taxpayers, most of whom never or rarely fly, should not be paying for that.

Biofuels cannot be scaled up rapidly enough and neither should this be the goal

Biofuel scale up has been promised by the aviation industry for more than a decade but this has not materialised. Targets have been routinely missed by significant margins and then ambition ratcheted down across successive years. For example, in 2009, the International Air Transport Organisation (IATA) was aiming for 10% biofuels by 201718 and in 2011, Air Transport Action Group (ATAG) stated: “We are striving to practically replace 6% of our fuel in 2020 with biofuel. We hope this figure can be higher”19. However, as of 2021, only less than 0.01% of jet fuel is biofuel20.

Even if we were to accept the industry’s most optimistic future projections of aviation biofuel use, they still do not expect that such fuels will provide a large percentage of total fuel consumption over the next few decades, given their plans for huge growth in air traffic and fuel consumption. For example, the EU has presented plans that will only put them on track to deliver 5% alternative jet fuel (mostly biofuel) by 203021. With limited quantities of biomass available and thus limited biofuel potential, the only way to deliver a greater overall percentage within meaningful timescales would be to decrease total fuel consumption. However, as stated above: even those limited quantities would compete with other applications and bring danger of human rights violations, emissions through land-use change and biodiversity loss. This makes biofuels a false solution on many different levels and a clear threat to meeting climate targets in a just manner.

End Notes & Literature

1 Global AG Investing (2019):
2 T&E (2019):
3 T&E (2019):
4 Milieudefensie (2020):
5 Biofuelwatch (2017):
6 BBC (2021):
7 Biofuelwatch:
8 CleanSky2&FCH (2020):, p. 18
9 ICCT (2021):, p 1-4
10 Department for Transport UK (2021):, p. 48-49
11 IATA (2021):
12 Department for Transport UK (2021):, p. 48-49
13 T&E (2019):
14 Lee, D et al (2021):, p.1
15 Vogt, C et al (2021):, p. 1
16 ICCT (2021):, p 1-4
17 ICAO (2019):, p. 20
18 IATA (2009):, p.14
19 ATAG (2011):, p.2
20 FlightGlobal (2020):
21 European Commission (2021):, Annex 1, p. 28

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Synthetic Electro-fuels

Alternative jet fuels or so-called “Sustainable Aviation Fuels” (SAF) are liquid hydrocarbon fuels that can be used with existing aircraft in place of kerosene produced from fossil fuels. The industry’s premise of the sustainability of these fuels is to create the fuel using CO2 taken from the atmosphere, rather than using fossil fuels extracted from deep underground that will then emit additional CO2 to the atmosphere when burned. The argument is that blending these fuels with fossil fuels would thereby reduce emissions.

Alternative jet fuel can be broadly categorised into two varieties:

  • Biofuels produced from biomass sources (see Fact Sheet 4)
  • Synthetic electro-fuels (e-fuels) produced using electricity (explained below)

Synthetic electro-fuels or “e-fuels” can be produced by combining hydrogen with carbon to create a liquid hydrocarbon. In order to minimise emissions, hydrogen must be extracted from water by electrolysis using renewable energy; and carbon must be extracted from the air using a process called ‘Direct Air Capture’ (DAC). These can then be combined, to form a hydrocarbon fuel using Fischer-Tropsch (FT) synthesis1. The latter processes must also be powered with renewable energy.

E-fuels are also known as “Synfuels” or Power-to-Liquid (PtL) fuels. E-fuels, as well as biofuels, are drop-in fuels that could be blended with conventional fossil jet fuel (kerosene) and used by the existing fleet.

At first sight, e-fuels seem to be the ultimate weapon for decarbonising aviation: they should be able to be used directly in all types of current aircraft, whatever their range; they do not suffer from raw material limitations because they are made from water and air, which are very abundant resources; and the electricity required could itself be generated from the sun and wind, which are very abundant energies. So why are there no aircraft powered by these fuels yet and very few for another ten years or so? Mainly because the production of e-fuels is extremely wasteful of energy. It would deprive other sectors needing to decarbonise as there will not be enough renewable energy available to satisfy all the requirements in the next decades. Also because this is a new industry starting almost from scratch, that still needs to complete process development and set up a whole new sector.


Happening soon
E-fuels could start to be blended with kerosene in 2030.

Zero emissions
Their production would not cause any CO2 emissions and their combustion would just return to the atmosphere the CO2 from where it would be extracted.



Government support required
Due to the significant extra cost governments should provide financial support for e-fuels, so that aviation industry growth is not affected.

Too late
E-fuels do not address the climate emergency. Although the technology has been demonstrated, it’s still at the pilot stage and several decades of heavy investment would be needed to scale up production.



Not zero
Even if CO2 emissions can theoretically be reduced down to zero, they would still generate NOx and contrail cirrus that have twice as much climate impact than CO2 today.

Requires huge quantities of renewable electricity
E-fuels require even more energy to produce than hydrogen, which would deprive other sectors needing to decarbonise.

Very low energy efficiency
No more than about 10% of the electricity used would be converted into thrust to move an aircraft, whereas it can be used with a much better efficiency in most other applications.

Financial support from governments means taxpayers pay
Most of whom rarely or never fly… Subsidies for e-fuels risk wasting public money on an expensive solution and would keep flying artificially cheap, resulting in more air traffic and emissions than if the industry paid.


E-fuels cannot be scaled up rapidly enough to meet climate targets

The deployment of e-fuels is likely to be slow and last several decades. Very few countries have concrete plans for implementation. Currently, only the EU is considering a mandate for e-fuels which starts at only 0.7% in 20302 and the NGO Transport & Environment believes that an objective of more than 1% in the EU would be challenging3. This is far behind the emissions reduction pace that must be achieved in order to not exceed the globally agreed 1.5°C heating target: according to the United Nations Environment Program (UNEP), worldwide greenhouse gas (GHG) emissions must be reduced by 55% by 20304.

E-fuels would only partially reduce non-CO2 emissions

Additionally, aviation should not only reduce CO2 emissions but also non-CO2 emissions that have twice as large a climate impact today5. Whereas CO2 emissions of e-fuels could theoretically be reduced to zero if CO2 is extracted from the air and renewable electricity is used to produce hydrogen and in all the other processes, this is far from being the case for non-CO2 impacts. Recent estimates indicate that e-fuels will not contribute to reducing non-CO2 impacts by more than 12% versus kerosene6.

Producing e-fuels would require huge quantities of renewable electricity that would deprive all other sectors that need to decarbonise

E-fuels could be part of a new economy of hydrogen aiming at replacing fossil fuels where electricity is not a possible alternative. But their production would require huge quantities of renewable electricity: not only must hydrogen be produced from electricity with significant energy loss, but making synthetic fuels from hydrogen requires further process steps with even higher energy losses. Hydrogen needs to be combined with CO2 and the resulting fuel must be processed and purified to make it usable by aircraft engines. CO2 must be extracted from the atmosphere using “Direct Air Capture” (DAC) at high energy cost due to its dilution. No more than about 10 % of the electricity spent would be converted into thrust to move an aircraft7.

Using renewable electricity to make e-fuel therefore looks like a crazy idea because energy requirements would be huge, whereas renewable electricity is crucially needed to decarbonise the global economy and can be used with a far higher efficiency in most other applications. For example, electricity powering a battery-electric coach results in an approximate 77% power-to-motion efficiency8, which is 8x better than if used for an e-fuel powered flight in an aircraft!
For the decades to come, the production capacity of renewable electricity will still not be enough to:

  • Replace fossil fuel in power plants that supply the electricity grid
  • Help satisfy new demand for electricity (cars, heating/cooling, data, etc.)
  • Replace today’s grey hydrogen (produced from fossil fuels) used for industrial processes e.g. fertiliser production
  • Satisfy new demand for hydrogen for trucks, ships, aviation…
In a scenario where 100% of the airliner fleet would use e-fuels in 2050, the resulting electricity demand would be 20% higher than the current total worldwide electricity production and 4.7 times the production of renewable electricity in 20189! As demand for electricity grows so does the risk that renewable electricity supply won’t be able to match that demand, which will increase the risk of using non-renewable power.

Governments should not subsidise aviation
e-fuels: the polluter should pay

The complex process and the huge energy requirements will result in high costs: e-fuels cost six to nine times the price of kerosene in 2020 and would still cost 2 to 3 times more in 205010. Governments will therefore be asked for subsidies. These would keep flying artificially cheap which would result in more air traffic and emissions than if the industry were to pay the costs themselves. Taxpayers, most of whom never or rarely fly, should not be paying for that.

Other lesser known issues

The industry is facing a dilemma over the production of the CO2 required: achieving the highest climate impact reduction (60%), would mean extracting diluted CO2 from the atmosphere at very high energy expense, when concentrated CO2 is still available in large quantities from industrial exhaust/chimneys (cement, steel, refineries…). However, if CO2 was to be extracted from factory exhausts, this would just be using fossil fuel a second time and still result in additional emissions ending up in the atmosphere. The climate impact reduction would then drop down to 30%11.

Another rarely mentioned issue is that the manufacturing process produces a mix of hydrocarbons, of which only 50-70% is suitable for aviation12. This means that about 30-50% of the renewable electricity used in the process would be wasted for by-products that could be obtained in more efficient ways or for which there are better alternatives.

E-fuels will long be a precious commodity, rare and expensive, that should not be widely used in the future to replace kerosene in quantities much larger than today if the industry keeps growing.

End Notes & Literature

1 The Royal Society (2019):
2 European Commission, (2021):, Annex I, p. 28
3 T&E (2021):
4 UNEP (2019):, p. 15
5 Stay Grounded (2020):
6 CleanSky2&FCH (2020):
7 Ausfeder, F. et al (2017):
8 T&E (2020):
9 CleanSky2&FCH (2020):, p. 44
and IEA:
10 CleanSky2&FCH (2020):, p. 48
11 CleanSky2&FCH (2020):, p. 21
12 Novelli, P. ONERA, (2021):

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Net Zero & Carbon Neutrality

Reaching “net zero” targets is currently the central goal set in nearly every climate strategy – be it industry or government. For its part, the aviation sector has committed to reach net zero CO2 emissions by 2050.

According to the IPCC1, net zero CO2 emissions are achieved when any remaining anthropogenic CO2 emissions are balanced globally by anthropogenic CO2 removals. This means with the net zero concept, some “hard-to-abate” emissions are still allowed, provided that equivalent quantities of CO2 are removed from the atmosphere. Net zero CO2 emissions are also referred to as carbon neutrality. When all greenhouse gases are taken into account, this is referred to as net zero emissions.

Balancing residual emissions is promised via Carbon Dioxide Removal; this is a range of processes that remove CO2 from the atmosphere in addition to the removal via natural carbon cycle processes. It can be achieved either by increasing biological or geochemical sinks of CO2 or by using industrial processes to capture CO2. Carbon Dioxide Removal is one of two types of carbon offsets2 besides credits for ‘avoided’ emissions.


Reaching net zero will prevent climate breakdown. If we balance CO2 emissions to net zero by 2050, then we’ll align with the Paris Agreement goal for global heating not to exceed 1.5 °C.

We have the technology. There are a range of technological options that can be relied upon to provide credible emission pathways towards net zero whilst still allowing air traffic to grow.

Resorting to CO2 removal will be necessary. We’ll not be able to reduce all aviation CO2 emissions by 2050 and therefore will need to resort to CO2 removal to reach net zero.

Non-CO2: Not enough data, no action. Effects of non-CO2 emissions are not well enough understood and quantified to be included in net zero plans.

We are addressing the issue. Net zero plans are a means of taking responsibility for climate impacts and mitigation.

Too slow, too late. All that matters is the cumulative emissions in the atmosphere. So net zero by 2050 will be irrelevant if aviation’s fair share of the global carbon budget for 1.5 °C is exceeded long before 2050.

Technology is unproven and resource intensive. We cannot wait: we need to reduce emissions now, which means decreasing air traffic.

Appropriation of CO2 removal by aviation would not be equitable. One sector cannot appropriate the limited potential of CO2 removal to offset its own remaining emissions, thus buying its way out. What we need instead is a fair, global allocation of the remaining carbon budget.

Non-CO2: Too large to be ignored. The precautionary principle therefore requires that they are also included and reduced.

Our children will pay the price. Corporations and governments use the net zero by 2050 goal to diminish the sense of urgency, disguise inaction today and evade responsibility.

Reaching net zero by 2050 will not prevent climate breakdown: it’s far too late

After an initial unambitious commitment in 2009 to halve its CO2 emissions in 2050 compared to 2005, the International Air Transport Association (IATA) stepped up its target in October 20213, announcing that it was aiming to achieve ‘carbon neutrality’ by 2050. It claimed it would align aviation with the Paris Agreement’s goal of limiting global heating to 1.5 °C and unveiled its plans. As we shall see, this new target remains largely insufficient and only postpones efforts to reduce emissions that should be made much earlier and more massively.

Indeed, what matters in order to achieve the Paris Agreement objective is not the level of emissions in 2050, but rather the cumulative quantity of greenhouse gases that will be released into the atmosphere over the next 30 years. The only equitable way to meet the Paris Agreement target is to allocate a fair share of the global carbon budget to aviation, i.e. a fair share of the amount of CO2 that can still be emitted before the 1.5 °C heating threshold is exceeded and to adjust air traffic to fit within this budget. As this study shows4, aviation’s carbon budget will be exceeded well before 2050 if air traffic does not begin to decline. Technologies proposed to make aviation greener are still uncertain and will take too long to develop and deploy if they ever can be.

Reaching net zero in 2050 may temper the rise in temperature, but cannot keep global heating under the 1.5 °C or even the 2 °C threshold. It would then no longer be enough to aim for net zero, but require negative net emissions and removal of much larger quantities of CO2 to attempt to salvage a livable climate.

The technological promises will not be kept. They are unproven and too resource-intensive

The sector’s strategy is largely based on the promise of technological solutions and it uses these to justify its continued growth. It has a variety of so-called ‘sustainability’ strategies: improving aircraft and operational efficiency; using alternative fuels with reduced CO2 emissions; and developing alternative propulsion systems (electric and hydrogen). As we demonstrate in other fact sheets (Fact sheets 1-5), “efficiency improvements” have always resulted in increased emissions and alternative fuels pose too many resource problems to be deployed quickly in the massive quantities required. As for hydrogen and electric aircraft, they are not feasible before 2050 for medium and long-haul flights, which currently account for the majority of aviation (CO2 and non-CO2) emissions. So it’s very likely that there will be far more remaining emissions than projected by the sector.

We cannot therefore rely on technology to respond to the climate emergency. The only solution to rapidly reduce aviation emissions is to reduce air traffic.

One sector cannot appropriate the means to remove CO2 from the atmosphere, especially since they are not available or proven at scale

Despite plans to use alternative fuels and technological innovation, airlines are predicting that they will not be able to completely eliminate CO2 emissions by 2050 and will need to resort to a variety of means to remove previously emitted CO2 from the atmosphere. IATA estimates that 19% of the remaining emissions will need to be offset, i.e. 342 million tonnes (Mt)3. In addition to the current methods of offsetting, which are mainly based on capturing CO2 through biomass, there would also be a need to capture CO2 from the air using industrial processes (Direct Air Carbon Capture and Storage: DACCS).

Net zero or real zero? Our ecosystem is not just maths

The concept and logic of net zero or carbon neutrality is in itself problematic and needs a closer look. Particularly from indigenous communities, we see strong resistance against this concept because it supports the scientifically false illusion that it is easily possible to restore the lost balance between the climate and ecosystem through compensation and so-called “nature-based solutions” (NBS). As industrial processes like DACCS have their own problems6 and are unproven at scale, most net-zero promises still heavily rely on NBS. But while fossil carbon is the result of millions of years of sequestration, the carbon stored in living ecosystems cycles much quicker and cannot be counted as permanent sink to equate to the emissions from fossil carbon. The carbon emitted by a flight will affect the climate for thousands of years. A forest planted as compensation could burn down in 20 years and release the stored carbon. Net zero promises are leading to a growth in demand for offsets which leads to further commodification of nature. The diversity of our planet’s ecosystems is turned into tradable carbon, often including land grabbing from Indigenous Peoples in the Global South8. The NGO CLARA has developed a short guide and indicators to read net zero pledges and unveil the negative impacts and false assumptions behind them9.

This 342 Mt value is still a lot and very unlikely to be feasible, since the potential for CO2 removal is limited and will have to be shared with other sectors. Moreover, the very idea that one sector would appropriate (by paying more than others) part of the limited means available to compensate for the emissions it doesn’t want to reduce is contrary to the concept of carbon neutrality, which can only apply at a global scale1.

In any case, the land managed by humans is today a net global emitter of carbon, due in particular to deforestation and forest fires. This will remain so for many years before the situation is reversed and biomass becomes a net carbon absorber5. Actions to restore or increase biomass must first compensate for its continuing destruction. As for industrial processes, they are only at the demonstration stage and have not yet been proven to be deployable on a large scale. Furthermore, DACCS is a very inefficient use of scarce renewable energy, which can provide far greater emissions reductions if used to power the grid, road transport or heat buildings6.

Net zero CO2 by 2050 is an illusion. Too far away from meeting the requirements of the climate emergency and giving the false impression that it’s as easy to remove CO2 from the atmosphere as it is to dump it. This is thermodynamically absurd7.

Current aviation net zero roadmaps only  include CO2; they must also include non-CO2 impacts   

Aircraft generate emissions other than CO2, mainly NOx and condensation trails (contrails) which, when transformed in the atmosphere, have a climate impact best-estimated to be twice as large as that of CO2. The total emissions impact of air transport is therefore most likely three times greater than that of CO2 alone10.

The aviation sector is using the uncertainty surrounding the quantification of these impacts as a pretext to oppose any regulation, even though promising simple measures are in sight9. Furthermore, they are deliberately distracting people from the fact that implementing these measures – as well as reducing air traffic – would massively and rapidly reduce aviation caused heating because non-CO2 emissions have a higher global warming potential (GWP) and a much shorter lifetime than CO2.

Instead of denial, the precautionary principle should be applied, which would mean that the sector should be eliminating both CO2 and non-CO2 emissions.

Far from taking responsibility, the aviation sector is using net zero CO2 as a way to continue its growth and postpone action

Even if net zero CO2 is achieved by 2050, the sector will have emitted far more than it should have in order to avoid exceeding 1.5 °C. It will be leaving all ecosystems and both present and future human generations with a ‘carbon debt’ that will need to be paid off (if eventually possible) by removing massive amounts of carbon from the atmosphere, while having to cope with increasingly difficult climatic conditions and reduced resources to survive. It’s also notable that aviation emissions aren’t currently being priced to set aside future money for this debt. Rather, air travellers can effectively emit for free today, and somebody else (future taxpayers) will have to deal with the consequences tomorrow.

According to UN projections11, keeping global heating below 1.5 °C would require a 55% reduction in emissions by 2030 and net zero emissions by 2050. While the 2030 and 2050 targets are inseparable, the aviation sector is only committed to the more distant one because it refuses to reduce air traffic now, which is the only way to achieve the 2030 target. It is deceptively buying itself time by suggesting that it still has time to continue business as usual. It doesn’t.

The fake carbon neutrality of airports

Some airports claim carbon neutrality but this is a fallacy because it only concerns a very small part of their emissions. The emissions included are confined to Scope 1 (emissions from airport controlled sources, e.g. buildings) and Scope 2 (emissions from energy purchased by the airport).

88 airports around the world claim to be carbon neutral. This label has been awarded to them by ACA12, an organisation belonging to the Airports Council International (ACI). It means that these airports have taken steps to reduce and/or offset (by purchasing carbon credits) the emissions over which they consider themselves to have control. Some are for example building solar farms on their premises or planting trees and presenting that as an offset. They see no obligation to reduce (or offset) Scope 3 ‘indirect’ emissions, because they are considered not under the airport’s direct control, although they account for more than 99% of total emissions related to airports13,14. Most of these emissions are from flights and from ground transport used by passengers and airport workers travelling to/from an airport.

While the development of new technologies and fuels may be helpful, it cannot be an excuse to delay emissions reductions that are needed NOW to mitigate the climate crisis. The only way to effectively reduce aviation emissions is to reduce air travel. To achieve this, we need effective regulations to limit air traffic.
In our Degrowth of Aviation15 report, we lay out how a set of measures could lead to a just reduction of aviation. In our Just Transition16 paper, we present the idea of how a conversion of the aviation industry can guarantee security for the livelihood of workers.

End Notes & Literature

1 IPCC glossary:
2 Stay Grounded (2017):, p. 9-10
3 IATA (2021):
4 ISAE-SupAero (2022):, p. 158-159
5 IPCC AR6 WG3 SPM (2021):, p. 6
6 The CCC (2020):, p. 11
7 Recharge (2021):
8 FoE International (2021):, p. 18
9 CLARA (2022):
10 Stay Grounded (2022):
11 UNEP (2021):, p. XXIII
12 ACA: 88 airports had achieved the
12 Neutrality, Transformation or Transition level in September 2022.
13 ADP (2018):, p. 22-30
14 DGAC (2020):, p. 7, 9
15 Stay Grounded (2019):
16 Stay Grounded (2021):

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While research and development of new technologies is important, it cannot serve as an excuse to delay the emissions reduction that is needed NOW if we are to prevent a climate catastrophe.

Alternative fuels or alternative technology won’t be able to significantly replace fossil fuels in the near future and have their own issues. Therefore we need to degrow energy-intensive activities, such as aviation and save existing and evolving renewable energy for other sectors. To achieve this we need effective regulations to limit air traffic. In our report on Degrowth of Aviation we lay out how a set of various measures could lead to a just reduction of aviation. In our Discussion Paper on Just Transition we present the idea how a conversion of the aviation industry must and could guarantee security for the livelihood of workers. For more detailed information on offsets, emission trading systems and commodification of nature have a look at our report on Green Flying.