The aviation industry body Sustainable Aviation has just released a road map to net zero by 2050. While this is a welcome change in ambition from the previous industry-set target of halving emissions by 2050, it rests on a lot of assumptions which don’t stand up to close examination and it has some important omissions which will make it difficult or impossible to keep global heating to 1.5C.
Given the uncertainties, a plan to allow aviation to grow 70 per cent in the next 30 years is reckless and the report does not offer a credible road map to decarbonisation. If we allow this to happen vast amounts of carbon will have to be removed from the atmosphere by technologies that are currently unproven and untested. With the aviation industry likely to be one of the biggest contributors to climate change as other sectors decarbonise more rapidly, getting it right is critical for the UK to meet its emission targets.
Carbon emissions are only half the problem
The report notes that it will be focusing only on the CO2 impacts of aviation. This ignores the fact that the non-CO2 impacts of aviation on the climate are roughly double the impacts of CO2 alone. As the Paris Agreement is a target to keep warming to within 1.5 degrees, ignoring the non-CO2 impact of aviation is not a responsible approach. At present, the only definitive way to reduce the non-CO2 impacts of aviation is to have fewer planes in the air, which is at odds with Sustainable Aviation’s plans for a 70 per cent increase in passenger numbers.
In terms of CO2, the report suggests significant carbon savings can be made through better efficiency in air traffic management (ATM) and the use of sustainable aviation fuels (SAF) made from biomass rather than fossil fuels.
The scale of the savings suggested by Sustainable Aviation are unlikely to be realised. The Department for Transport has assessed the opportunity for ATM to contribute to decarbonisation and found it to be zero, only just able to keep up with the increased pressure from more planes in the air.
‘Sustainable Aviation Fuels’ are not exactly sustainable
The claims around SAF are more credible, in that the Committee on Climate Change agrees that they can play a role in decarbonising the sector. The CCC suggests that, by 2050, SAF will make up between five to ten per cent of the aviation fuels market. Sustainable Aviation, however, assume a 32 per cent market share and that carbon savings of SAF over fossil fuel will be 70 per cent.
These assumptions do not agree with academic literature estimates of the carbon savings possible from SAF. A study conducted by the US Argonne National Laboratory suggested that, depending on the source of the feedstock, between 55 and 85 per cent savings could be realised. A more recent study of the EU suggested that, if waste sources of biomass were used, 70 to 90 per cent savings are possible.
However, if energy crops are used, 60 per cent savings are the best possible scenario and some crops will actually increase overall emissions. This is important as, as the Energy Transitions Committee notes, by 2050 the demand for sustainable biomass will vastly outstrip supply, meaning a full spectrum of feedstocks will be used, not just the best ones. As an example, oilseed rape, an energy crop which can be grown in the UK, only gives a 40 per cent saving in emissions.
There is competition for scarce resources
The figures in Sustainable Aviation’s report would only stack up if a commitment were made to give all of the most sustainable biomass to the aviation sector. This would be to the detriment of the rest of the economy. In reality, any alternatives to fossil fuel are likely to be from a mix of multiple sources depending on biomass availability, price and policy. And other sectors, such as the fledgling bio-based plastics industry, also have plans to use the same low carbon waste biomass to bolster their own green credentials.
Future plans to create completely zero carbon fuels from captured CO2 are technically possible, but will need rapid development and are likely to make flying extremely expensive. Until these are proven and deployed at scale, it would be wise to be cautious on aviation growth.
Continued growth is a risky strategy
Given the lack of a plan to deal with non-CO2 heating effects, the practical limitations on availability of sustainable feedstocks for fuel, and the need to prove and develop truly scalable technologies, a plan that allows 70 per cent growth in flights over the next 30 years is vanishingly unlikely to be compatible with 1.5C heating. If truly net zero e-fuels and technologies to capture and store carbon from the atmosphere can be developed and deployed at scale, then aviation may have a route to sustainable growth. But in the meantime, the only responsible course is to limit demand.
Until it has a more credible plan to decarbonise and address its non-CO2 impacts, it would be reckless to allow the aviation industry to continue to grow unchecked. Although support for lower carbon fuels is welcome, allowing growth at the rate the report suggests would leave the UK at risk of missing its legally binding greenhouse gas emission reduction targets.
It is good that the industry sees the need to act and is signalling that it will invest in solutions. But what is needed is a clear commitment to end airport expansion, steps to lower demand in a fair way and incentives to adopt the most carbon efficient planes and fuels possible.
