AEF: Claim that new jet fuel from waste will massively cut aviation CO2 is dangerously misleading

UK Government has launched new funding to spur the development of “sustainable aviation fuel” (SAF) from waste. There have been claims that US scientists have found a way to ‘massively reduce carbon emissions from flying’. The benefits of the novel way to make jet fuel are exaggerated. The Aviation Environment Federation (AEF) says that the claims require some very dodgy carbon accounting. They are adding the methane that might be generated by decomposing rubbish, and assumptions about carbon emissions – but ignoring the CO2 emissions produced when the fuel is burnt. In fact these emissions would be slightly higher, from waste-derived fuel, than conventional fuel, as it has a slightly higher carbon content.  A better way to prevent methane from rotting landfill waste would be to cut food waste, divert biodegradable rubbish away from landfill sites and use methane capture technologies there. Cait Hewitt of AEF said “any government incentives for use of alternative fuels for aviation will need very clear and transparent guidelines to ensure that they actually cut aviation emissions, to avoid this kind of accounting smokescreen in future.” Government is  In the meantime, cutting back on flying is easily the best way of reducing aviation emissions.”



16th March, 2021

By AEF (Aviation Environment Federation)

A press story yesterday[1] claimed that US scientists had found a way to ‘massively reduce carbon emissions from flying’.

In fact, though, the ‘up to 165%’ emissions reduction claimed by the report authors arises largely from supposed savings as a result of preventing methane emissions that would otherwise arise from landfill, together with ‘carbon credit incentives’ for using energy sources other than fossil fuels. When the fuel is burnt in an aircraft the emissions it generates would actually be higher, the authors admit, than from burning conventional fossil fuels, as a result of its slightly higher carbon content[2].

Methane generated by rotting landfill waste is a powerful greenhouse gas. Cutting food waste, diverting biodegradable rubbish away from landfill sites and putting in place methane capture technologies can all help to tackle these emissions. For the UK to achieve net zero, these steps need to be delivered in addition to – not instead of – the decarbonisation of aviation.

The BBC story was published the day before the UK Government launched new funding to spur the development of Sustainable Aviation Fuel from waste[3]. There will also be a consultation this year on potential mandates for the purchase of ‘sustainable aviation fuels’ with a view to stimulating the market for these fuels, which are currently significantly more expensive than kerosene (which remains untaxed).

AEF deputy director Cait Hewitt said:

There seems to be some very dodgy carbon accounting behind the claim that this fuel will cut emissions from flying. Genuine answers to the aviation emissions problem are in fact still few and far between.

Any government incentives for use of alternative fuels for aviation will need very clear and transparent guidelines to ensure that they actually cut aviation emissions, to avoid this kind of accounting smokescreen in future. Including international aviation emissions in carbon budgets would be one way to help ensure proper accountability for this sector, which has so far fallen through the net when it comes to climate policy.

In the meantime, cutting back on flying is easily the best way of reducing aviation emissions.

Between 1990 and 2019 emissions from international flights departing UK airports increased by 138%. In the year the UK will host the global COP meeting, green groups have highlighted the need for government action on aviation emissions[4].


Contact: Tim Johnson // Cait Hewitt

Notes to editor:

[1] Climate change: Jet fuel from waste ‘dramatically lowers’ emissions

[2] See page 24

[3] Jet Zero launches £15 million competition to reduce aviation emissions

[4] Open letter: Government must include aviation and shipping in net zero legislation


Climate change: Jet fuel from waste ‘dramatically lowers’ emissions

By Matt McGrath
Environment correspondent (BBC)

Read with caution – there is a lot of dodgy carbon accounting in this.

A new approach to making jet fuel from food waste has the potential to massively reduce carbon emissions from flying, scientists say.

Currently, most of the food scraps that are used for energy around the world are converted into methane gas.

But researchers in the US have found a way of turning this waste into a type of paraffin that works in jet engines.

The authors of the new study say the fuel cuts greenhouse gas emissions by 165% compared to fossil energy.   [sic]

This figure comes from the reduction in carbon emitted from airplanes plus the emissions that are avoided when food waste is diverted from landfill.  [There are other, better, ways of dealing with the methane problem, other than turning it into jet fuel, to be burned at 36,000 ft – adding non-CO2 climate impacts. AW comment]

The aviation industry worldwide is facing some difficult decisions about how to combine increased demand for flying with the need to rapidly cut emissions from the sector.

In the US, airlines currently use around 21 billion gallons of jet fuel every year, with demand expected to double by the middle of the century. At the same time, they have committed to cutting CO2 by 50%.

With the development of battery-powered airplanes for long haul flights a distant prospect at this point, [so distant that it is either extremely unlikely ever, or not for at least 30 years. AW comment] much attention has focussed on replacing existing jet fuel with a sustainable alternative.
In fact the UK government has just announced a £15m competition to encourage companies to develop jet fuel from household waste products.

Making paraffin from wet-waste

Current methods of making green jet fuel are based on a similar approach to making biodiesel for cars and heavy goods vehicles.

It normally requires the use of virgin vegetable oils as well as waste fats, oil and grease to make the synthetic fuel.

At present, it is more economical to convert these oils and wastes into diesel as opposed to jet fuel – which requires an extra step in the process, driving up costs.

Now, researchers say that they have developed an alternative method able to turn food waste, animal manure and waste water into a competitive jet hydrocarbon.

Much of this material, termed wet-waste, is at present is turned into methane gas. However, the authors found a way of interrupting this process so it produced volatile fatty acids (VFA) instead of CH4.

The researchers were then able to use a form of catalytic conversion to upgrade the VFA to two different forms of sustainable paraffin.  [There is, of course, no reason why these fuel could not be used for vehicles – heavy lorries etc – that need liquid fuel. They do not have to power aircraft.  AW comment] 

>When the two forms were combined they were able to blend 70% of the mixture with regular jet fuel, while still meeting the extremely strict quality criteria that Federal authorities impose on aircraft fuels.

“>”There’s exciting jet fuels that rely on burning trash and dry waste but this actually works for those wastes that have high water content, which we normally dispose of in landfill,” said Derek Vardon, a senior research engineer at the US National Renewable Energy Laboratory and the lead author on the study.


“Being able to show that you can take these volatile fatty acids, and that there’s a really elegant, simple way to turn it into jet fuel – that’s where I see the broader applicability of this one, and folks can continue to develop and refine it.”


The new fuel has a potentially significant impact on emissions as it not only limits the CO2 that comes from fossil sources used by the airlines, but it also gets rid of the methane that would bubble up from landfill if the waste food was just dumped.


Another major advantage is that this new fuel produces  [are they sure?] around 34% less soot than current standards. This is important because soot plays a key role in the formation of contrails from airplanes which adds a powerful warming effect to CO2 coming from the engines.

“>”That’s where we see the most potential for this technology is that you’re preventing methane emissions, and dramatically lowering the carbon footprint of jet fuel. And you just can’t do that with fossil fuels without getting into things like offsets,” said Derek Vardon.


The research team say they are planning to scale up the production of the new fuel and aim to have test flights with Southwest Airlines in 2023.


Many environmental groups are sceptical about attempts to develop sustainable aviation fuels, believing that it amounts to green-washing. They argue that people should just fly less.

“Sustainable aviation fuel is not a silver bullet,” Derek Vardon says.

“So we do want to definitely emphasise that reduction is the most important and most significant change you can make. But there’s also pragmatism and need for aviation solutions now, so that’s where we want to strike a balance as we need a basket of measures, to really start getting our carbon footprint down in a variety of sectors, including aviation.”

The study has been published in the Proceedings of the National Academy of Sciences (PNAS).

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