Jet zero: pie in the sky?

Can we really decarbonise aviation by 2050? The Government’s Jet Zero consultation thinks not, but we should be able to offset the residual emissions.

Aviation is one of the hardest sectors to decarbonise: the expected lifetime of aircraft is over 25 years, new aircraft designs take around 10 years and the potential range of low carbon fuels is limited. Although today aviation contributes only 2-3% of global greenhouse gas (GHG) emissions, unless we act now, its share will grow as other sectors decarbonise. By 2050, it could be the second largest contributor to UK’s emissions.

To address this, Government has published a package of policies: the Transport Decarbonisation Plan; a consultation on Jet Zero; and a consultation on a Sustainable Aviation Fuels mandate. It wants to set an even earlier net zero target of 2040 for domestic aviation and airport operations. Key themes emerging from the policies are:

Efficiencies

A quick win is to improve the efficiency of the aviation system, rather than wait for new technologies and fuels. There are three ways we could do this:

• increase the efficiency of conventional aircraft through design improvements. Research suggests that an updated version of an existing design typically provides 12-15% fuel consumption reduction, while more unconventional designs could deliver even higher reductions of up to 40%. Government estimates that replacing older aircraft still in operation with the latest models could save around 20 Mt CO₂ by 2050;
• changes to airport operations: use of a single engine for taxiing, increasing efficiency of airside vehicles, reducing aircraft weight by precisely matching fuel and water requirements with passenger loads, better maintenance procedures and optimisation of speed, route and altitude in flight planning; and
• airspace modernisation: more direct flight paths at more efficient altitudes and speeds and addressing holding in stacks for aircraft waiting to land at busy airports.

To achieve this, it is proposed that all airport operations in England should be zero emission by 2040 and that all airlines should sign up to a voluntary agreement to avoid tankering where there is no practical reason to carry additional fuel.

Wider policy changes may include consideration of environmental performance in the airport charges and/or slot allocation and possible use of formation flying, where the aircraft behind the lead aircraft take advantage of the wake energy.

But in the face of a growing demand, efficiency gains alone are not enough.

Zero emission aircraft

In the UK, hydrogen-electric and battery-electric aircraft have already been demonstrated and the potential of hydrogen and ammonia is being considered in longer term. But these are really only suitable for small aircraft on regional routes and the use of hydrogen-powered aircraft is unlikely to be feasible until after 2035.

For long-haul flights, that have the biggest impact on climate and may be more challenging to conduct by zero emission aircraft, biofuels are the most promising alternative for aviation, being largely compatible with the existing engines.

Biofuels

The proposed way forward is to scale up biomass-derived fuel made from waste feedstocks (Sustainable Aviation Fuel or SAF) which can be mixed with conventional jet fuel and blended into existing aircraft.

SAF faces significant operational and technology risks and financial and revenue uncertainty. To overcome these barriers, generate demand and encourage private investment, Government is proposing to introduce a SAF mandate in the UK from 2025.

Unlike the existing Renewable Transport Fuels Obligation (RTFO) which rewards SAF volumes, the SAF mandate will prioritise carbon emissions savings, so that only those SAF whose GHG emissions intensity is below a set target and meets specified technical criteria, will be eligible for credits.

Also unlike the RTFO, which is voluntary, SAF mandate would be a mandatory obligation on suppliers of jet fuel to the UK, possibly with a buy-out mechanism for those who fail to produce SAF. To avoid double-counting, any SAF supplied under the mandate will not be eligible for incentives under other schemes, in the UK or abroad (including RTFO, CORSIA, UK ETS and EU ETS).

Government believes that SAF use can reduce UK’s aviation emissions by up to 36% by 2050.

Offsetting

Markets will play a role in offsetting the residual emissions that remain after implementing the above measures.  Schemes include the UK Emissions Trading Scheme, which covers emissions from domestic flights, flights from the UK to the European Economic Area and flights between the UK and Gibraltar; the EU ETS; and the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).

CORSIA requires qualifying aircraft operators to monitor emissions on all international flights and offset the growth above the baseline in emissions from flights between participating states by purchasing and cancelling eligible emission units generated by projects that reduce emissions in other sectors (for example, renewable energy). The UK has committed to participating in the pilot phase and has already implemented the scheme’s monitoring, reporting and verification provisions. The offsetting provisions are expected to be implemented by April 2022.

Consumer travel choices

According to the Committee on Climate Change, 59% of emission reductions to reach net zero will involve some form of societal behaviour change. An example is to have journey planning apps that include carbon emissions data for different modes of transport. This would help influence travel choices.  Variations can be significant: one study has found that emissions per passenger can differ by up to 63% on the same transatlantic route.

To ensure that relevant data is available, Government is developing a Transport Data Strategy (TDS). It will also look at ways of rewarding those parts of the aviation sector that move more quickly to decarbonise.

Conclusion

With so much uncertainty and constraint, the best way of successfully decarbonising the transport sector is to pursue multiple options through policies that are durable and adaptive. The main hurdles are expected to be high costs (production of SAF, CCUS), supply constraints (biofuels) and uncertainty.