In 2024, aviation’s greenhouse gas (GHG) emissions were 38 million tonnes of carbon dioxide equivalent gases (MtCO2e). In addition, the global warming effect of aircraft contrails is at least as harmful as GHG emissions. Aviation now accounts for 8% of UK GHG emissions which makes it the UK’s sixth highest-emitting sector. This is not surprising, as a transport mode that lifts its passengers seven miles up and propels them at 500mph will always require much more energy than surface transport.
At the Railway Industry Association’s (RIA) annual conference, I asked Secretary of State for Transport Secretary Heidi Alexander if it was government policy to drive modal shift to more carbon friendly modes as achieving net zero aviation GHG emissions is far from certain.
She did not answer the modal shift question though the DfT press office subsequently advised that action is being taken to support the uptake of public transport and active travel. There are, however, no plans to follow the French example of banning domestic flights with a rail alternative of less that 2.5 hours. As shown in the table, GHG emissions per passenger on a London to Glasgow flight are 27 times greater than those of a rail passenger.
Responding to my question, Ms Alexander said that she “would probably take issue a little bit” about my views on net zero aviation. She described the sustainable aviation fuels (SAF) mandate which will steadily increase the current 2% of jet fuel that has to be SAF. She also mentioned improvements in aircraft efficiency and airspace modernisation to reduce flight distances. Yet the Government’s Jet Zero Strategy (JZS) shows that such measures will only reduce aircraft GHG emissions by 37% by 2050.
Jet Zero Strategy
The JZS considers that, with no mitigation, UK aviation emissions will be 52 MtCO2e by 2050. It describes the aircraft GHG emission measures mentioned by Ms Alexander but does not consider the cost of SAF which a DfT report considered to be “high and uncertain”. SAF is currently at least twice the cost of conventional jet fuel. Furthermore, a Royal Society report showed that replacing all UK aviation fuel with SAF produced from biofuel would require half the UK’s agricultural land.
The JZS also considers that, after implementing aircraft GHG emission reduction measures, the remaining residual emissions will have to be sucked out of the atmosphere. It predicts that this will be done by removing 19 MtCO2e by direct air carbon capture and storage (DACCS) and 14 MtCO2e by offsetting schemes (forestry and renewable energy). In this way the JZS believes that aviation net zero can be achieved by 2050 without any requirement to limit aviation growth.
The JZS additionally forecasts that UK domestic services will have zero emission planes by 2030 as there are now small aircraft powered by batteries and hydrogen. Yet this claim ignores the fact that aircraft weight increases exponentially with length. Moreover, replacing the 60 tonnes of fuel used in a transatlantic flight would need a battery weighing 800 tonnes.
As an alternative, Airbus is considering liquid hydrogen (as used in Saturn V moon rockets) which has 10 times the energy density of batteries. However, this hydrogen would take up a third of the fuselage. Moreover, powering all UK planes by green hydrogen would require more than half the UK’s current electricity generation to produce it.
The CCC view
The Climate Change Act required the creation of the independent Climate Change Committee (CCC) to advise government. Unlike the JZS, the CCC has consistently recommended a reduction in aviation demand growth. It also considers that the full cost of decarbonising aviation should be reflected in the cost to fly and estimates that, by 2050, this would add £300 to the cost of a return transatlantic flight.
The CCC considers that the JZS is “high risk” due to its reliance on unproven technology as DACCS has yet to operate anywhere at scale. As CO2 constitutes only 0.04% of the atmosphere, DACCS would require filtering of a volume of air equivalent to 30,000 Millenium Domes per day to remove the 19 MtCO2e of GHG required by the JZS. This would also require costly carbon capture and storage infrastructure which CCC figures indicate would require 5% of current UK electricity consumption and cost £billions per annum.
A CCC report on the effectiveness of offsetting found that it suffered from inaccurate claims, funded carbon reduction measures that would have happened anyway, and that different carbon credits were being used to fund the same project. Hence, the CCC concluded that emissions should only be reduced by offsetting as a last resort. A mature tree absorbs 25kg of carbon per year, offsetting the 14 MtCO2e of GHG required by JZS would require 600 million trees occupying a forest the size of Surrey, Suffolk, and Kent combined.
The CCC’s 2019 Net Zero report considered that aviation demand growth should be limited to 60% above 2005 levels by 2050. Its 2023 report to Parliament recommended that there should be no airport expansion without a demonstrable reduction in aircraft emissions. This is also the view of the Parliamentary Environmental Audit Committee. Government chose not to follow the advice of the independent body set up to provide climate change guidance. Instead, it relies on the JZS’s unconvincing claim that aviation net zero by 2050 is achievable.
In the last two years, aviation emissions have increased by 26% to 38 MtCO2e. With continuing aviation growth this makes it unlikely that the JZS target of 35 MtCO2e by 2030 will be achieved. The CCC considers that if this target is not met, policies to further reduce demand for flights will be required.
The UK aviation sector is an essential part of the UK economy and supports Britain’s aerospace industry. It also provides international connectivity to allow UK companies to access global markets and brings tourists, who spend billions of pounds, to the UK. Yet aviation is the most carbon intensive form of transport and, as both the CCC and JZC recognise, it is only possible to eliminate less than half of aircraft GHG emissions.
Telling it as it is
The scale of tree planting, air filtering, energy consumption, and costs associated with removing of 31 MtCO2e of GHG from the atmosphere each year show that JZS proposals for atmospheric carbon removals are not credible. Furthermore, it is not clear who will pay for the significant costs of DACCS and carbon credits which offer no benefit other than removing GHG.
The JZS advises that its aim is to “future proof aviation so passengers can look forward to guilt-free travel.” Yet, as this feature shows, it does this by disguising wishful thinking as certainties. The government’s aviation policy is therefore based on the false promise that aviation net zero is possible.
Instead of relying on JZS, government should follow the CCC’s advice. The reality of current, and likely future, aviation emissions should also be made clear to potential flyers so that they can choose whether to fly or, if possible, take more environmentally friendly surface transport.
Given aviation’s importance to the economy, it would not be unreasonable to accept that aviation cannot achieve net zero, though some form of demand management is surely necessary. For domestic flights, policies that encourage modal shift to rail would be a good idea.
Image credit: iStockphoto.com/oversnap