Sustainable Aviation Fuel Bill

Viscount Hanworth Excerpts

Thursday 20th November 2025 Lords Chamber

[Viscount Hanworth (Lab)]

My Lords, the carbon content of fossil fuels has been accumulating over eons by the removal of carbon dioxide from the earth’s atmosphere via biological processes of photosynthesis, depending on chlorophyll and powered by sunlight. Such processes are highly efficient in their use of energy but they are far too weak and gradual to remove from the atmosphere the quantities of carbon dioxide that have been emitted by burning fossil fuels.

Capturing this carbon dioxide requires artificial processes that are far less efficient than the biological processes and far more consumptive of energy. Only by expending a large amount of energy that could be supplied by nuclear fission, and possibly in the long run by nuclear fusion, can there be any hope of cleansing the atmosphere of its excess carbon dioxide. According to a recent analysis, about 3% of carbon emissions are due to aviation. This figure is rising. We have heard that it is about 7% of UK emissions. Jet aircraft consume high-octane kerosene, which is refined from petroleum. Each flight powered by hydrocarbons adds to the burden of atmospheric carbon dioxide. If global heating due to carbon dioxide is to be addressed, something must be done to staunch the carbon emissions of aviation.

The problem is that there is no viable means of powering long-haul aviation other than kerosene, which has an unequalled energy density. Moreover, the technology of jet turbines, which has developed over the past 80 years, is not easily replaceable. Electric batteries or hydrogen fuel cells can be used in short-haul aviation, but their weight penalty precludes their use in long-haul aviation. Hydrogen, which has been used to power space rockets, has been proposed as an alternative for aviation fuel. Hydrogen has a very high energy content per mass, which is significantly greater than that of gasoline, but it has a low energy density per volume, meaning that it requires a large space to store it, even when compressed or liquefied. Liquid hydrogen has an energy content of about 5.6 megajoules per litre, whereas gasoline has about 32 megajoules per litre—almost six times as much. To use hydrogen to power aircraft would require a technology radically different from the current aviation technology, which would take a long time to develop. Its efficiency in transporting passengers would be severely limited by the storage requirements of the fuel.

If we are to sustain the present aviation technology, we need to develop sustainable aviation fuels, or SAFs. The ultimate requirement for such fuels is that they should emit to the atmosphere no greater quantities of carbon dioxide than are removed from the atmosphere for the purpose of creating their carbon feedstock. At present, so-called sustainable aviation fuel, which forms a very small proportion of the total supply of fuel for aviation, depends on a carbon feedstock that originates in biomass. Such aviation fuel cannot be relied on to reduce significantly the net emissions of carbon dioxide. They can have a beneficial effect only if the net supply of biomass can be increased to cover their use.

There are three cases to consider. First, the carbon feedstock might be grown for the purpose without displacing any other processes, but this is unlikely to happen. Secondly, the feedstock might be freely available, such as materials that would otherwise be consigned to landfill. Finally, and at worst, the production of the feedstock could displace other activities, such as the growth of foodstuffs.

Only in the first case, where there might be a net increase in photosynthesis, could there be a subtraction from atmospheric carbon dioxide. In the other cases, the emission of carbon dioxide from burning the fuel would be more rapid than if it had resulted from the natural decay of the feedstock, which might gradually add carbon dioxide and methane to the atmosphere.

It should be observed that wood, unless it is burned, will lock away carbon for many human generations. Therefore, forestry products should not be used as a carbon feedstock for synthetic fuels. Sustainable aviation fuel will deserve its name only if its carbon content can be removed directly from the atmosphere via the so-called technology of direct air capture.

This Bill has the ambition of stimulating the production of sustainable aviation fuels. It proposes to do so via minor financial interventions modelled on those that intend to encourage investment in renewable means of generating electricity.

The Bill itemises three levels, or generations, of SAF production. The first-generation SAFs are made from hydrogenated esters and fatty acids derived from oils or fats, such as used cooking oil. The second-generation SAFs are to be made from waste sources, including so-called municipal solid waste. The third-generation SAFs, also known as power-to-liquid aviation fuel, are to be made by combining hydrogen produced by electrolysis and carbon monoxide, which can be produced from captured carbon dioxide.

Regarding the first generation of SAFs, hydrogenated esters and fatty acids—commonly described as chip fat, because that is their major source—are already pre-empted to produce biodiesel. There is a good deal of mystery and doubt surrounding the second generation of SAFs. Their primary feedstock, which is described as municipal solid waste, is poorly defined, and different processes will be needed to cope with different categories of waste. A website of the British company Johnson Matthey, which is proposing to build plants in the US and Germany to produce second-generation SAFs, mentions a variety of sources for the carbon feedstock, including agricultural residues, forestry biomass, captured carbon dioxide, and the ill-defined municipal solid waste.

At the heart of the second generation of SAFs is the venerable Fischer-Tropsch process, which was invented in Germany in 1925 and used extensively in Germany during the war to create synthetic fuels using coal as the predominant carbon feedstock. The process generates hydrocarbons from syngas, which is a mixture of carbon monoxide and hydrogen. The syngas will be the product of a gasification plant, which must be specific to the nature of the primary feedstock. If this process were to take its carbon dioxide from captured industrial emissions then it would emit carbon to the atmosphere that might otherwise be sequestered in the ground. The conclusion of this critique is that the only sure way of reducing aviation emissions would be to capture the carbon directly from the atmosphere. In that case, the Fischer-Tropsch process would continue to be used to synthesise the fuel.

The Bill appears to envisage a gradual transition between the three generations of SAF production, and it imagines that this can be achieved by financial incentives that could be structured by the Government. There would be no other government intervention and the Government would bear no costs. The costs would be covered by levies on the aviation industry and maybe by the suppliers of hydrocarbon fuels.

This is a weak proposal for addressing a crisis. The Bill has been inherited from the Conservatives, and it bears the marks of their social and economic philosophies. One might have expected a more interventionist approach from a Labour Government. One is reminded of how an early post-war Labour Government sought to revolutionise the supply of power to industrial and domestic users by creating a completely new industry: the nuclear industry. A similar endeavour would be required to create a sustainable aviation fuel industry, but there is little indication that this will be forthcoming.