11
Despite the pleasure I’ve derived from my flight-free journeys so far, I can (grudgingly) acknowledge the fact that not all air travel can realistically be canned. Aside from the issues it would cause for tourism (as we saw in chapter 7), there are plenty of other considerations: families spread across the globe, conferences and business collaborations that can only really happen in person, freight that needs to be transported by aircraft.
And, if that’s the case, surely we need to be focusing all our attention and energy on the future tech that has a shot of decarbonising aviation. Just how far away are we from zero-emissions or carbon-neutral flights?
The good news is that there are several avenues being pursued in this space, some of them with truly exciting potential. The bad news is that the real technological game changers are a long way off making it into the realm of widespread commercial flights. Take my hand, dear reader, as we jump down the rabbit hole and into the world of the aviation techno-fixes – the good, the less good and the just plain problematic …
More efficient aircraft
This is the least sci-fi, most practical method for reducing flight emissions, and it’s something that’s already happening on a wide scale. Upgrading an airline’s fleet by swapping old jets for aircraft models with more efficient engines, can have a significant impact – for example, exchanging four-engine aircraft for modern long-haul twin-engine aircraft can represent an increase in fuel efficiency of more than 20 per cent per passenger.1
Airlines globally have been cranking up their investment in modernising their fleets in recent years; Jet2 said it had put in a ‘new order for up to 60 Airbus A321 NEO aircraft, which is in our view the most efficient and environmentally friendly aircraft in its class today’ in its 2021 sustainability strategy, while easyJet said it would be ‘transitioning its fleet to increasingly more modern, fuel-efficient aircraft, flying them in ways which maximise fuel efficiency, and optimising passenger loads as much as possible’.
Carbon dioxide emissions per passenger flight have fallen more than 50 per cent since 1990 due to improved engines and operations.2 However, improved efficiency in current aircraft technology has in no way increased in line with emissions growth. Between 2013 and 2019, passenger transport-related CO2 emissions increased by 33 per cent, according to a study by the International Council on Clean Transportation (ICCT).3 Over the same period, the number of flight departures increased 22 per cent and revenue passenger kilometres (RPKs) increased 50 per cent. ‘This means that passenger air traffic increased nearly four times faster than fuel efficiency improved,’ reads the report.
Though more efficient planes replacing creaky old models will reduce carbon emissions in-flight, evidently there won’t be any real benefit if there’s no curb on growth of the number of flights overall.
‘Modernizing fleets and improving operational efficiency are important; however, in the best case, annual industry growth counters the emissions that they save,’ according to analysis by consultancy McKinsey.4
Sustainable aviation fuel
Sustainable aviation fuel (SAF) is the latest Great White Hope that the aviation industry is throwing all its energy behind.
In 2021, it was as if the sector had collectively committed to this as the new party line. IAG, the group that owns British Airways, Aer Lingus, Iberia and Vueling, was the first European airline group to commit to powering 10 per cent of its flights with SAF by 2030;5 the same pledge was made by all airlines in the One World Alliance (which includes American Airlines, Cathay Pacific, Qantas and Qatar Airways) a few months later;6 and US airlines announced they aimed to use 3 billion gallons of SAF a year by 2030 after the White House promised to issue funding and fiscal incentives for the use of biofuels.7
British Airways, the UK flag carrier, said ahead of the COP26 conference in November 2021 that it would source SAF to take delegates between London, Glasgow and Edinburgh during the event, as well as committing to investing £290 million into SAF development over the next twenty years.8
But what actually is SAF? And how does it compare, emissions-wise, to traditional aviation fuel?
What is SAF?
From an outside perspective, all of the above sounds very positive. Airlines are taking the initiative and vowing to change. And SAF must be, well, sustainable, right? It’s right there in the name, for crying out loud! Au contraire, mon ami. At this point, I think we’re all well aware of the sometimes chasm-like gap between sustainability claims and sustainability reality.
Most SAF in practice is jet fuel that’s produced from ‘sustainable’ feedstocks, such as waste cooking oil and other non-palm waste oils from animals or plants; solid waste from homes and businesses, such as packaging, paper, textiles and food scraps that would otherwise go to landfill or incineration; forestry waste, such as waste wood; and energy crops, including fast-growing plants and algae. It’s very similar in its chemistry to traditional jet fuel – which is why airlines are going so big on this as the aviation panacea. For SAF to be used in aircraft, it must have ‘drop-in’ characteristics – automatically be compatible with existing aircraft technology, with a performance comparable to or exceeding existing fossil fuels during the combustion process – which, simply put, means airlines can use SAF in the aircraft they already have.9 Aside from the more efficient aircraft solution outlined above, it’s the cheapest, easiest method of adaptation to achieve lower emissions from flying without having to reduce the number of flights (which, as we know, they are exceptionally keen not to do).
Another fuel type that sits under the SAF umbrella, and which is potentially pretty exciting, is synthetic fuel, also known as e-fuels or synfuels. These are derived from hydrogen and captured carbon emissions and require water, renewable electricity (to produce hydrogen) and CO2. These fuels are several times the cost of conventional kerosene at the moment, ‘though we expect a significant cost reduction for green hydrogen (via reduced costs of renewable electricity and “electrolyzers”) in the coming years’, according to McKinsey. It envisages that, in the short-term, the CO2 could be captured as waste gas from carbon-intensive industries, such as steel, chemicals and cement, with longer-term production methods using direct air capture (DAC – remember this from our look at the offsetting options?) to extract the necessary CO2 from the atmosphere.
However, ‘While synfuels could become an answer to cutting emissions over the long run, it is unclear, at this point, which SAF sources will emerge as winners,’ writes McKinsey. All of the above fuels are way more costly than kerosene; it’s a chicken-and-egg scenario, where airlines don’t have a viable business case for scaling up SAF, so the production volume is small, so there’s no economy of scale to make it cheaper.
How much carbon does it save?
One key thing to note before we look at the numbers is that this kind of fuel must currently still be blended with traditional jet fuel – the non-SAF kind – in order to be compatible with existing planes. SAF can be blended at up to 50 per cent with traditional jet fuel – so when an airline says a flight is being powered by SAF, it could be that half of the fuel (or likely more) being used is still of the fossil variety.10
In general, the number that airlines and the oil industry all bandy around for SAF is 80 per cent. ‘SAF gives an impressive reduction of up to 80% in carbon emissions over the lifecycle of the fuel compared to traditional jet fuel it replaces, depending on the sustainable feedstock used, production method and the supply chain to the airport,’ says BP.11
There are a fair number of caveats in that statement. First and foremost, it would be more accurate to say that SAF has ‘the potential’ to save this; second (and second-most), the ‘up to’ bit is quite important – it certainly doesn’t mean that all or even most SAFs will be hitting this figure. And then we get to perhaps the most telling part – all of the above is based on ‘the lifecycle’ of the fuel. The wording is important: note that it is not claiming that this results in 80 per cent fewer carbon emissions from a SAF-powered flight compared to a kerosene-fuelled one.
It’s all a bit sneaky, because if you’re not reading the fine print, you could easily be forgiven for thinking SAFs saved in-flight emissions. But the reality is that SAFs emit at least as much CO2 as kerosene.12 At least as much. Additionally, SAF-powered flights produce the same amount of harmful non-CO2 emissions, which also have a significant warming effect.
The greenhouse gas savings all come in the production stage, when the fuel is manufactured (for example, with some biofuels, fast-growing plants are used, meaning carbon has been removed from the atmosphere in the process). With the right balance – particularly in the case of synfuels using DAC, if the same amount of carbon was being removed from the atmosphere in the creation of the fuel as was then emitted when it was burned at altitude – this could arguably lead to carbon-neutral flights. Nifty, huh?
But often this ‘life cycle’ approach to fuel emissions is not based on carbon removals, but rather makes assumptions about what would have happened to, for example, the waste used to make the SAF if it hadn’t been turned into a fuel. The AEF says:
As waste with a high proportion of ‘biogenic’ material in it can generate methane – a powerful greenhouse gas – if left to rot, a large benefit is assumed to arise if the waste is instead turned into aviation fuel even though this still generates at least as much CO2 as fossil kerosene once burned.
The claimed ‘net’ reduction therefore relates to avoided emissions rather than to any actual reduction. But to achieve net zero by 2050 across the economy, these methane emissions will need to be avoided as well as aviation emissions reaching net zero, not instead. 13
What are the problems?
Even with the aforementioned considerations, SAFs should be preferable to traditional kerosene if they’re less emissions-intensive in their production (and, in some cases, remove carbon in the process). But there are a number of other stumbling blocks to watch out for.
One of them is scale. As we saw, airlines – and the industry in general – are making some big claims about the projected use of SAFs by 2030. The thing is, this isn’t the first time they’ve laid down impressive-sounding pledges. ‘Aviation biofuel scale-up has been promised by the industry for more than a decade but this has not materialised,’ wrote Finlay Asher from Safe Landing, a group of workers within the aviation industry who raise awareness of the climate reality of aviation, in an article entitled ‘The Trouble with SAF’.14 ‘Targets have been routinely missed by significant margins, and then ambition ratcheted-down across successive years. There was a target for 25% by 2020, but SAF use is currently at less than 0.01%.’
According to McKinsey’s analysis, in a 1.5°C pathway (as defined by the Paris Agreement), SAF would have to account for 20 per cent of all jet fuel by 2030 – or, at a minimum, 10 per cent, ‘in a scenario in which transportation lags in decarbonisation compared with other sectors’ (looking pretty blooming likely at this stage).
And yet a 2021 paper from the ICCT, which estimated SAF feedstock availability to meet growing European Union demand, concluded:
Without taking into account the political or economic barriers to SAF production, we estimate that there is a sufficient resource base to support approximately 3.4 million tonnes (Mt) of advanced SAF production annually, or 5.5% of projected EU jet fuel demand in 2030. The estimated production potential takes into account feedstock availability, sustainable harvesting limits, existing other uses of those materials, and SAF conversion yields.15
It’s unclear, then, how myriad airlines expect to be able to meet even the underwhelming 10 per cent SAF target by that same year.
The scaling up of synfuels is even further away – 2030 is looking like the earliest point at which these could be successfully blended with kerosene. It will then clearly take a significant amount of time before production in any meaningful quantities can be achieved.
Another sticking point is resource. Various biofuels come from ‘virgin crops’, not from waste; land is used for ‘energy’ crops, including palm oil, rapeseed or soy. This can be ‘hugely damaging’, according to Finlay, as they’re a leading driver of deforestation and are a nightmare when it comes to biodiversity. ‘The overall effect is that using biofuel can be worse than using fossil fuel,’ he argues.
Land use is a hot-button issue in this context too. To properly scale up the production of this particular type of SAF, land currently used for food production would need to be used to grow biofuel crops instead. Finlay says:
Biofuel has been scaled up for road transport and it’s had a devastating effect on land in places like Malaysia, Indonesia and some countries in South America, leading not only to a decline in biodiversity but also humanitarian effects such as water shortages, rising food prices, and land conflicts.
Synfuels might on the surface look more promising but present their own resource issues. Creating liquid hydrocarbons is an energy-intensive process. The idea is to use renewable energy to power this – but we only have a limited amount of renewable energy available. ‘We should be prioritising the use of renewable energy in powering our homes and our road transport before we start to power aviation,’ writes Finlay. When we look at any energy use, there is a hierarchy of need – with transport, particularly aviation, coming near the bottom of the list. A 2020 independent study projected that it would take three to four times the current global renewable energy generation to produce enough synthetic e-fuels for aviation based on current consumption trends.16
In the UK, at least, it looks as if the government is addressing some of the above issues. In a set of proposals published in July 2021, there was a commitment not to allow SAFs from food or feed crops, and not to divert renewable energy from other applications into making e-fuels.17 The proposals also focused on fuels capable of delivering high carbon savings that generally avoided direct or indirect land use or wider environmental impacts.
Only a small range of fuels was identified as meeting these criteria: waste-derived biofuels, renewable fuels of non-biological origin (RFNBOs), SAF from nuclear energy and recycled carbon fuels (RCFs). While on the one hand acknowledging and addressing these issues is to be commended, on the other it significantly curtails the scale to which you could realistically ramp up SAF use – rather than being the ‘big solution’ the aviation industry has been presenting it as.
‘In fact these fuels may be a rather small and/or expensive solution, and there’s a big danger in creating the illusion of climate action while in fact continuing very largely with business as usual,’ says the AEF.18
So, should we just dismiss SAFs? Not necessarily – they could certainly have a place in the future of a lower-carbon aviation industry. But at present there doesn’t seem to be a clear pathway of how this would be scaled up to what’s needed to make a significant impact without further detriment to the planet; and, crucially, it won’t put a stop to the emissions produced by flights themselves. Even the name ‘sustainable aviation fuels’ is probably misleading at this stage, suggesting that passengers will be stepping aboard some magic, zero-carbon aircraft.
Safe Landing’s Finlay summed it up thus: ‘There might be a place for SAF, but it must go hand in hand with an overall reduction in fuel consumption. As ever, the most reliable way to reduce emissions from aviation is to fly less.’
Hydrogen-powered and electric planes
There are two technologies currently in development that are capable of offering real, bona fide, zero-carbon flights: liquid hydrogen and electricity.
The former, H2 propulsion, eliminates CO2 emissions in-flight and can be produced carbon-free. Estimates show that H2 combustion could reduce climate impact in-flight by 50–75 per cent and fuel-cell propulsion by 75–90 per cent, compared to around 30–60 per cent for synfuels.19 Hydrogen also means a significant reduction in the other non-carbon emissions associated with aviation that contribute to global warming (nitrogen oxides and water vapour, for example). The only waste product it produces is clean water, and it packs in three times more energy per unit of mass than conventional jet fuel, plus more than a hundred times that of lithium-ion batteries.20 Ooh la la!
According to a 2020 study by Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings, ‘hydrogen propulsion has the potential to be a major part of the future propulsion technology mix’.
‘The 2020s will be the “Decade of Hydrogen”,’ said Ron van Manen, head of strategic development at Clean Sky Joint Undertaking:
There is no viable path to a zero carbon or climate neutral aviation system that does not involve hydrogen: whether in liquid form as a true ‘zero carbon’ energy source, or as a key building block in the liquid fuels of the future.
A fair amount of investment is going into the development of this technology. In 2020, a partnership between California-based start-up ZeroAvia and various other enterprises, backed by the UK government, saw the successful maiden flight of a hydrogen-powered, six-seater Piper M-Class from Cranfield airfield.
ZeroAvia’s Founder and Chief Executive Val Miftakhov said the company expects to offer commercial flights by as early as 2023; flights of 500 nautical miles (926km) in aircraft with up to eighty seats by 2026; and 100-seater single-aisle jets by 2030.21
Airbus, the world’s largest aircraft manufacturer, announced in September 2020 that hydrogen-fuelled propulsion systems would be a key element of its ZeroE project, which will see it produce a new generation of zero-emissions aircraft. Hydrogen ‘is one of the most promising technology vectors to allow mobility to continue fulfilling the basic human need for mobility in better harmony with our environment’, Grazia Vitaldini, chief technology officer at Airbus, said.
The French planemaker has presented three aircraft designs, all of which will be hybrids, combining gas-turbine engines that burn liquid hydrogen with electricity generated via hydrogen fuel cells.
The other possibility garnering attention is that of electric planes. These are powered by one or more electric motors that drive propellers, with the electricity usually sourced from batteries or solar cells.
Developments have come thick and fast over the last few years. In 2017, Slovenian aircraft manufacturer Pipistrel developed one of the first all-electric planes, which was certified for use in flying schools. In 2019, Harbour Air completed the world’s first successful all-electric commercial aircraft flight; its ePlane, a six-passenger DHC-2 de Havilland Beaver, flew for half an hour over the Canadian Fraser River. This was swiftly followed up in 2020 by AeroTEC and magniX, who created the biggest commercial plane to take off and fly powered solely by electricity. The nine-seater modified Cessna Caravan 208B, dubbed the eCaravan, flew for thirty minutes after taking off from Grant County International Airport in Washington state. The flight, though brief, was incredibly cost-effective: around £4.80 as opposed to the £240–320 it would have cost using engine fuel.
Airbus, meanwhile, has made progress with this over the last decade. In 2010 it developed the world’s first all-electric, four-engine aerobatic aircraft, CriCri; it followed this up with an all-electric, twin-propeller aircraft, the E-Fan, which successfully crossed the English Channel in 2015. It has since been working on electric vertical take-off and landing (eVTOL) projects, and in 2021 launched its inaugural ‘electric airplane race’, the world’s first all-electric aircraft race.
Designing for Uber Air, American planemaker Boeing has created an electric passenger air vehicle capable of being fully autonomous, with a range of up to 80km. The idea is that it will provide a flying taxi service, potentially rolled out to customers within the next few years.
One of the big goals on the table is to develop a 180-seater electric plane that could cover 500km (roughly the distance between London and Cologne in western Germany). EasyJet has partnered with start-up Wright Electric to design a prototype with the aim of achieving this and being able to operate commercial electric flights from 2030. These would likely be used initially only on very short-haul hops, such as London to Paris.
The drawbacks
If all of the above sounds like a blessed utopia of zero-carbon flying, I’m afraid I’ve got some bad news (when don’t I?). There’s a reason – in fact several – that no one is talking seriously about these two techno-fixes being the saving grace for the future of aviation.
For starters, both have significant built-in limitations with regards to capacity and distance. Assuming all necessary technological and infrastructure developments happen over the next five to ten years (a significant barrier in itself that we’ll look at in a moment), H2 propulsion ‘is best suited for commuter, regional, shortrange, and medium-range aircraft’, according to the Joint Undertakings report. As it stands, it’s very difficult to see how hydrogen could possibly be used for long-haul flights.
This is due in part to the volume of liquid hydrogen needed to power flights. Hydrogen has higher energy by mass than jet fuel, but lower energy by volume – so you need four times the volume of hydrogen compared to that of kerosene.22 For a journey of the same distance, you would therefore need a fuel tank four times the size in your lovely H2-powered aircraft – not so lovely when you consider that’s taking up valuable space that can no longer be used for cargo or passengers, and is adding significant weight into the bargain.
With electric planes, the issue is very much weight-based. Batteries’ lower energy density compared to fuels means aircraft would need to carry more than 50kg of battery weight to replace 1kg of kerosene (based on current technology).23 Oh boy. And because battery weight doesn’t decrease as the plane flies – unlike fuel, which burns off, making the aircraft lighter and more efficient as it travels – extra energy is required to carry the extra burden. This affects longer flights in particular. Plus, current batteries are a more awkward and cumbersome shape to be accommodated in comparison to liquid fuel, which can be stored in the aircraft wing.24
Dr Duncan Walker, an applied aerodynamics expert at Loughborough University, calculated that the world’s largest passenger plane, the Airbus A380, could fly just 1,000km powered by batteries compared to its usual range of 15,000km.25 ‘To keep its current range, the plane would need batteries weighing 30 times more than its current fuel intake, meaning it would never get off the ground,’ he said.
‘The use of fully electric aircraft carrying more than 100 passengers appears unlikely within the next 30 years or longer,’ according to McKinsey’s analysis.
Aside from that, when we consider hydrogen propulsion, we must return to our infrastructure problem. Unlike the SAF ‘solution’, the hydrogen techno-fix requires an entirely new, very expensive set-up, in addition to new aircraft.
Although ‘smaller aircraft powered with hydrogen could become feasible in the next decade’, according to McKinsey, ‘for aircraft with more than approximately 100 passengers, significant aircraft-technology development would be required, and infrastructure constraints would need to be overcome.’
Airports would need new parallel refuelling infrastructures, including fuel trucks able to store liquid hydrogen; refuelling times would grow for longer-range aircraft, which would in turn impact on airport gate and aircraft utilisation.
‘Creating a hydrogen infrastructure will be critical: no infrastructure means no ZEROe aircraft,’ said Glenn Llewellyn, VP of zero-emission aircraft for Airbus. ‘We will need efforts from energy providers, airports and the entire aviation industry in order to make it possible to refuel our ZEROe aircraft at airports in the future.’
Although the Joint Undertakings report champions the use of hydrogen, it acknowledges that ‘as a disruptive innovation it will require significant research and development, investments, and accompanying regulation to ensure safe, economic H2 aircraft and infrastructure mastering climate impact’.
Cost will be a significant barrier too. Hydrogen fuel is around four times the price of kerosene at present. As improvements are made, that gap will get smaller – but it’s still likely to remain around double the price for the next few decades.26 This alone will put airlines off pursuing it in any meaningful capacity, unless they’re forced to do so by some kind of legislation.
You see the problem? For this to be developed and rolled out with any kind of urgency, at any kind of scale, it needs a huge, coordinated effort from all the key stakeholders in the industry. It would take a monumental amount of investment in airports around the world, in addition to the development of all the necessary tech (which would then need extensive testing, as with everything in the air-travel sector, to ensure safety isn’t compromised).
‘Our belief is that it will take a while for all the technology and elements of hydrogen propulsion to be worked out before we can get to … commercial use,’ Sean Newsum, director of environmental strategy at Boeing Commercial, told the Financial Times.27
It’s why these solutions, though clearly the most likely to achieve truly ‘zero-carbon’ flights, are only seen as playing a marginal role in reducing the aviation industry’s carbon emissions in the next thirty years.
The bottom line
If it isn’t obvious by now, all the techno-solutions that have thus far been identified come with their own challenges and pitfalls.
The ‘cleanest’ fixes are also the ones with the biggest hurdles – financially and technologically – and they’re also the ones likely to take the most amount of time to implement due to infrastructure constraints.
The less clean ones – namely SAFs – are easier to put into practice but come with their own sizeable issues in terms of scalability, cost and question marks about whether they are really better for the planet depending on how they’re sourced and produced.
More and more weight and money is being thrown behind R&D for all of this stuff – but even the most optimistic projections don’t see a massive overhaul of the current system happening anytime soon. All of it is difficult and expensive; using untaxed kerosene is easy and cheap. There’s therefore still very little incentive for the industry to aggressively pursue even the more problematic alternatives that are available.
I think it’s clear that, at some point, the ingenious human race will achieve carbon-neutral flying – it’s only a matter of time. But time is the thing we no longer have when it comes to making the reductions necessary to meet that 1.5°C climate target. This tech will not conclusively solve the problem of aviation emissions in the next ten, twenty or thirty years. And with 2050 as the big, booming deadline, that’s simply not good enough.
As far as I can see, there is no way around it: reduction will be necessary. We need to fly less, no matter what noise the industry makes about SAF, synfuels, H2 propulsion, electric planes or whatever else. Technology is an incredible tool in our arsenal – but it isn’t, and never has been, a magic wand.