What we think about so-called Sustainable Aviation Fuel…

Alternative aviation fuels and the industry’s greenhouse gas problem: a briefing.

The need to buy time for solutions and adopt the precautionary principle by not allowing airports to expand unless alternative fuels and new technologies are proven to work at the scale and pace required for the UK aviation industry to reach net zero by 2050

Summary

The UK has a legally binding commitment to reach net zero greenhouse gas emissions by 2050. In 2019, UK aviation (international and domestic) accounted for 8% of UK carbon emissions, with non-CO2 emissions tripling the climate impact of flying, according to the latest science. Without significant change, aviation is likely to be the second highest emitting sector in the UK by 2050.

The term ‘sustainable aviation fuels’ has been coined by the aviation industry to cover a range of potential alternative fuels for aircraft. However, the true ‘sustainability’ of these alternative fuels, and their prospects for scaling up at the pace needed, must be assessed – not assumed. This is particularly important for the next government, which will have to make carefully considered choices about how to facilitate a green economic transition with limited funds available to invest.

In brief, a great deal of uncertainty remains and not all alternative fuels are equally effective at reducing emissions within individual aircraft, across the whole economy and across the world. There are different outcomes, risks and limitations in relation to actually reducing the greenhouse gases (CO2 and non-CO2) caused by flying, depending on what type of alternative fuel is used and what assumptions are made when conducting life-cycle assessments of their sustainability.

Independent assessments by a range of reputable organisations warn of the high probability that there are currently no alternative fuels or technologies, either alone or in combination, that can credibly solve aviation’s greenhouse gas problem within a climate relevant timescale.

That is, there is a high risk that UK aviation will not be able to reach net zero by 2050, especially if the predicted 60% increase in demand by 2050 is allowed to continue unchecked.

As a result of the high level of uncertainty and risk, the government’s expert statutory advisers on the Climate Change Committee have repeatedly recommended that there should be no expansion of UK airport capacity unless an aviation emissions mitigation strategy is in place and proven to be working on the scale and at the pace required for the industry to become net zero by 2050. We are asking you, the next government, to follow the Climate Change Committee’s advice.

What are the alternative fuel options for aviation?

We start with a definition of what is included within the aviation industry’s term ‘sustainable aviation fuels’ because different types of alternative fuels have different pros and cons. In this paper, we include the following as alternative fuel options for flying and briefly set out the pros and cons of each:

  • Biofuels
  • E-fuels
  • Electricity
  • Green hydrogen

Biofuels: made from biomass, used cooking oil, household, agricultural and other waste

Pros:

  • CO2 is produced but is mitigated by CO2 capture in the biomass over time
  • Can be blended with fossil jet fuel and therefore avoid the need for radical transformation of aircraft design and airport infrastructure
  • Can be used for short, medium and long haul flight

Cons:

  • When burned in a jet engine, biofuels immediately release the same quantity of carbon emissions as fossil jet fuel
  • Biofuels can only reduce emissions on a ‘net’ basis, like carbon offsets – there’s no actual cut in the carbon emitted by flying but there could be a reduction from other natural processes (growing trees and plants) or industrial processes (carbon capture and storage) elsewhere
  • Plant based biomass feedstocks (trees, miscanthus, forestry residue,etc) take different lengths of time, varying from years to decades, to re-grow and re-capture carbon from the atmosphere
  • Carbon capture and storage technology is at a very nascent stage of development, with almost no examples of prototype projects succeeding in practice
  • There are only limited amounts of genuinely sustainable biofuel feedstocks and these are already in demand to decarbonise other sectors that may be seen as having a higher priority for the green economic transition – eg road travel, agriculture
  • It is not realistically feasible to scale up biofuel production to the quantities needed for the UK aviation industry’s current level of demand, nor for its predicted 60% growth by 2050 – as of 2021 only 0.01% of jet fuel was biofuel
  • The Royal Society estimated that half of all the UK’s agricultural land would be needed to grow energy crop feedstocks to meet current UK aviation fuel demand 
  • Importing biomass feedstocks seriously risks creating demand that would result in loss of biodiversity, deforestation, food insecurity and human rights violations elsewhere in the world
  • For example, clearing biodiverse, old growth forests and displacing local communities to produce palm oil to sell to the aviation fuel supply industry would result in a net increase in emissions and loss of carbon storage capacity in forests
  • A lifecycle analysis score cannot, on its own, tell us whether or the extent to which any particular alternative fuel is or is not sustainable at a whole economy or global level
  • Lifecycle analyses show different amounts of carbon savings for different feedstocks but these outputs vary significantly depending on the assumptions made in lifecycle assessments – the wrong assumptions could result in a net rise in emissions at a whole economy or global level
  • Non-CO2 emissions, which have a very strong climate impact (tripling the total warming effect of flying) can only be partially reduced by using biofuels

E-fuels (aka synthetic or power-to-liquid fuels): made from renewable electricity, green hydrogen and direct capture of carbon from the air

Pros:

  • Can be made using electricity that is only derived from renewable sources
  • Can be blended with existing fossil jet fuel and therefore avoid the need for radical transformation of aircraft design and airport infrastructure
  • Can be used for short, medium and long haul flight

Cons:

  • E-fuel production is a very nascent technology and industry, as yet unproven at scale – it will be a long time until e-fuel makes up a significant portion of UK aviation fuel
  • Scaling up to the quantity required by 2050 is unlikely because of the very large amount of renewable electricity needed, which is also needed to decarbonise other sectors that may be seen as having a higher priority for the green economic transition – eg energy, industry
  • For example, if a third of all UK aviation fuel use by 2050 is e-fuel, this would require renewable electricity equivalent to the consumption of approximately 14 million households
  • Renewable electricity can be used more efficiently in other sectors
  • For example, only 10% of the electricity used to make e-fuels would be converted into power to move an aircraft compared with electricity powering a coach, which would result in approximately 77% power-to-motion efficiency
  • The Climate Change Committee notes that capturing CO2 for e-fuel production delivers a similar net CO2 emissions reduction as capturing an equivalent amount of CO2 to be stored and continuing to use fossil fuels in the air
  • Non-CO2 emissions, which have a very strong climate impact (tripling the total warming effect of flying) would only be partially reduced

Electricity: aircraft powered by batteries that store electricity made from renewable sources

Pros:

  • Can be powered by electricity that is only made from renewable sources
  • Produces no CO2 from an aircraft’s tailpipe
  • Can be used on small aircraft going relatively short distances

Cons:

  • Scaling up depends on there being sufficient renewable electricity supply alongside demands from other sectors – eg energy, road transport
  • Electricity cannot work on larger aircraft, nor for medium or long haul flights, because of the limited power storage and extra weight of the batteries – 1 kg of fossil jet fuel equals 25 to 30 kg of batteries and the weight of batteries does not reduce during the flight, unlike liquid fuels
  • Electric powered flight is a significantly less efficient use of renewable electricity where options exist to travel on the ground

Green hydrogen: made by using renewable electricity in a process called electrolysis, to create a liquid fuel which is then stored at minus 235 degrees C

Pros:

  • No CO2 is produced from an aircraft’s tailpipe if renewable electricity is used to create hydrogen
  • Could be used for short or medium haul flight

Cons:

  • Green hydrogen production is a very nascent technology, as yet unproven at scale – hydrogen powered aircraft currently only exist on paper
  • Scaling up to the quantity required by 2050 is unlikely because of the very large amount of renewable electricity needed, , which is also needed to decarbonise other sectors that may be seen as having a higher priority for the green economic transition – eg energy, road transport
  • The Royal Society estimated that producing sufficient green hydrogen fuel to meet current UK aviation demand would require 2.4-3.4 times the UK’s entire 2020 renewable electricity supply
  • Green hydrogen powered flying is not feasible for long haul flights within the next three decades
  • Using green hydrogen would require radical and expensive redesign of aircraft and airport infrastructure which would take a long time – fleet renewal takes about 25 years
  • Non-CO2 emissions, which have a very strong climate impact (tripling the total warming effect of flying) would only be partially reduced

Cost: all types of alternative aviation fuels are likely to be significantly more expensive to produce than conventional fossil jet fuel. The aviation industry is lobbying hard for major public subsidies for production, especially for biofuels which it regards as its only short-medium option to reduce carbon.

We believe the aviation industry should meet the full costs of attempting to scale up biofuel supply. Research shows that 75% of the UK population takes no flight at all, or just one flight, in any given year. By contrast, 20% of the population takes 70% of all flights. It would be unfair to use taxpayer’s money to subsidise an activity that is disproportionately enjoyed by a relatively wealthy minority.

Climate Change Committee’s key recommendation for aviation: stop expanding airports

In its 2023 Progress Report to Parliament, the Committee reiterated its deep concerns with the Conservative government’s Jet Zero Strategy, describing it as ‘high risk’. That is, the current Conservative government policy of allowing airport expansions, and relying on alternative fuels and other new technologies to decarbonise aviation at some point in the future, is highly likely to result in UK aviation failing to reach net zero by 2050.

The Committee’s key recommendation was:

No airport expansions should proceed until a UK-wide capacity management framework is in place to annually assess and, if required, control sector GHG emissions and non-CO2 effects. A framework should be developed by DfT in cooperation with the Welsh, Scottish and Northern Irish Governments over the next 12 months and should be operational by the end of 2024. After a framework is developed, there should be no net airport expansion unless the carbon-intensity of aviation is outperforming the Government’s emissions reduction pathway and can accommodate the additional demand. (R2023-037).

We are asking you, the next government, to follow the Committee’s advice. Please impose an immediate three year moratorium on all airport expansions unless there is credible evidence that alternative fuels and new technologies are actually reducing aviation’s emissions at the scale and pace required for the UK aviation industry to reach net zero by 2050.

Independent assessments of alternative aviation fuels

Contact details

This paper was produced by the campaign group No Airport Expansion in March 2024:

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