With family equally divided between North America and Europe, I am doomed to an immoral life of using commercial airplanes to interact with them in person, between continents. Of course, additional immorality comes from flying for pleasure within Europe.
This weblog post reflects on the content of The six problems aviation must fix to hit net zero, an article by Joycelyn Timperley appearing in The Observer 2021-09-05. In it, she commented: Aviation is a complicated sector to decarbonise. It has some prickly ingredients: difficult technological solutions, hidden extra climate effects, an association with personal freedoms and a disproportionately wealthy and powerful customer base.
Almost four and a half years later, this weblog post will use her subject headings, but look what has happened in the intervening years, to address these issues. The first comment is that journalist Timperley is attempting to quote people to support her arguments. I have eliminated these quotations because they are general and unoriginal.
1. The fuel problem
Flying requires a lot of energy, and fuels with high energy density. I disagree with the premise that fossil fuels are the only available option for airplanes. One answer is to insist on the use of synthetic fuels, commonly called sustainable aviation fuels (SAF). This may require engine manufacturers such as Rolls Royce, to make/ modify engines specifically designed for the fuel. Even if fossil fuels continue to be used, they should be priced to ensure that the damage they contribute to the planet can be fully mitigated. There is no reason why the equivalent quantity of CO2 and other waste gasses cannot be scrubbed from the atmosphere, to make a carbon neutral product. SAFs accounted for less than 0.1% of aviation fuel consumption in 2018, in 2023 it was still less than 0.1%.
The fuel efficiency of aircraft improves over time. There is no magic involved, just the out-phasing of older aircraft with more efficient new aircraft. For example, switching from an older Boeing 747s to a more efficient Boeing 787s or Airbus A350s, can reduce carbon emissions by up to 30%. However, this improvement will not reduce total emissions. If aviation is becoming about 3% more efficient each year, passenger demand is increasing by about 5% a year.
In 2021, the European Commission presented the Fit for 55 package: a series of proposals to make the EU’s climate, energy, land use, transport and taxation policies fit for reducing net greenhouse gas emissions by at least 55 % by 2030, compared with 1990 levels. The European Commission proposes obligations on fuel suppliers to provide a minimum share of SAF that increases over time. The main goal is to increase use of SAF, resulting in a reduction of overall aviation emissions. A major problem with these commission proposals, is that the numbers are not concrete, with adherence voluntary. This will result in most airlines ignoring the proposals to avoid increased costs.
SAF is technologically ready for use, but a European Union framework to increase SAF is not. Other governments, such as the UK, want at least 10% SAF in place by 2030. There seems to be no plan to increase that to anything above that level. There are currently less than 6 years to ramp up from 0.1 to 10%. Regulations in effect restrict SAFs to 50% of fuel used. The first SAF-powered transatlantic flight, Flight100, involved a Virgin Atlantic Boeing 787, equipped with Rolls-Royce Trent 1000 engines. It took place 2023-11-28 between London Heathrow and New York JFK. This demonstrated that such journeys are possible.
The SAF used on Flight100 was: 88% HEFA (Hydroprocessed Esters and Fatty Acids) supplied by AirBP and 12% SAK (Synthetic Aromatic Kerosene) supplied by Virent. HEFA is made from waste fats, SAK is made from plant sugars, with the remainder of plant proteins, oil and fibres continuing into the food chain. SAK is needed in 100% SAF blends to give the fuel the required aromatics for engine function.
The real reason SAF is not used has to do with its price. Airlines as well as their customers prioritize lower costs. This means that regulators, government or international, will have to impose relevant regulations to ensure useage of SAF.
Despite many believers the most promising sustainable fuels will not be made from waste biofuels, like used cooking oils. They may be cheap and offer good life-cycle emissions, but its supply is limited. Even if all of these fuels were used exclusively for aviation, they would only provide about 2% of jet fuel use in the EU and US. In other words, it is not a solution.
Biofuels can also be made from crops such as palm, soya and corn. However, environmental groups have been arguing against these because they can compete with food production and drive deforestation – proposed EU legislation that aims to ramp up SAFs specifically excludes their use. Advanced biofuels from cellulosic plants and agricultural and forestry waste show more promise.
A final type of fuel that could be used in current aircraft is “electrofuel”, made using clean electricity and hydrogen. In theory, these could have an “almost unlimited supply”, says Rutherford, but they are currently very expensive to make.
There are also completely different kinds of aircraft on the horizon. While the size and weight of current battery technology mean electric propulsion is still a long way off for larger aircraft, electric planes are appearing on shorter routes. Yet, one of the key areas where electric aircraft need to make an impact, is with flight schools. For example, the Slovenian Pipistrel Velis Electro aircraft are in use for pilot training at Green Flight Academy in Skellefteå, Sweden. Starting in 2019, several smaller electric aircraft have appeared in this weblog: A retrofitted Beaver at YVR airport in Richmond, British Columbia;
Some companies are working on new kinds of aeroplanes designed to run on hydrogen gas, which could also be produced using clean electricity. Last year, Airbus revealed its concept for a hydrogen aircraft that it said could enter service by 2035, although it has also admitted such planes won’t be widely used until after 2050.
Chances of being solved? Clean fuels are likely to be used more and more but will make up only a few percent of fuel by 2030 and are unlikely to make a significant impact until after 2050.
2. The non-CO2 problem
Aviation accounts for about 2.5% of global CO2 emissions, but its warming impact is far larger because of other gases and particulates it emits at high altitudes. These are often called non-CO2 impacts, these include nitrogen oxides and contrail clouds = line-shaped vapor trail clouds produced by aircraft engine exhaust or changes in air pressure, typically at aircraft cruising altitudes several km above the Earth’s surface. They are composed primarily of water, in the form of ice crystals. These are rarely specified in aviation climate goals, but they could triple the climate impacts of aviation compared with CO2 alone.
What’s problematic, but also promising, about these effects is that they vary substantially depending on the surrounding climatic conditions. For example, one study found that just 2% of flights contribute to 80% of contrail warming effects. Night-time flights are particularly bad, because contrails produce their warming impact mainly at night.
It’s important to note that low-carbon fuels can still produce non-CO2 impacts, although these are expected to be lower than for kerosene for most fuels.
Chances of being solved? Unlikely in the near term given low prominence. However, the EU is beginning to pay more attention to this issue.
3. The frequent flyer problem
Some argue technological solutions will be too slow to reduce emissions in the aviation sector, and measures to reduce the amount people fly are needed to limit the damage to the climate.
But flying is not an evenly spread activity. In the UK about 15% of the population take 70% of all flights, and around half of people don’t fly at all in any given year. “That’s a pattern replicated in many other counties,” says Cait Hewitt, policy director at the Aviation Environment Federation (AEF).
The inequality in flying is even more stark at a global level. One study estimated that just 1% of the world’s population emits 50% of CO2 from commercial aviation, while just 2-4% of people fly internationally in a given year.
Some campaigners therefore support a “frequent flyer levy” as a fairer way to limit aviation emissions. The UK campaign A Free Ride argues everyone should have one annual flight free from the levy, then pay a rising charge for every extra flight taken that year. The UK’s first climate assembly also backed the idea of a frequent flyer levy.
The problem with such a levy is that many people in the frequent flyer category are likely to have the wealth to pay a moderate levy, or to have it paid by their employers, says Wood.
Manuel Grebenjak, a campaigner at the Stay Grounded network, says measures to limit flights overall, such as banning flights on certain routes, could help to stem rising emissions in a fairer way. “If a flight is banned from a certain city to another one, no one can fly, so it’s very just,” he says.
France has already moved to ban domestic flights on routes that can be travelled by train within two-and-a-half hours. Even just providing an alternative to flying can be effective: new high-speed rail lines have reduced aviation transport on the same routes by up to 80%, according to the International Energy Agency (IEA).
Chances of being solved? Governments,including the UK, tend to shy away from demand management approaches to limiting aviation emissions, but France and Austria are making good first steps.
4. The policy problem
All this feeds into a wider need for strong policy to tackle aviation emissions, which has largely been lacking so far. “International aviation sits outside the Paris climate agreement, because that agreement is about a country’s domestic emissions,” says Harvey. “So there was a real push to have a scheme for international aviation.”
After years of inaction, in 2016 countries at the UN aviation agency, ICAO, agreed on the Carbon Offsetting and Reduction Scheme for International Aviation (Corsia), a global deal to “offset” the growth in aviation emissions above the average levels in 2019 and 2020. However, when flights plummeted during the pandemic, countries changed the baseline of this scheme, which means there are currently no obligations on airlines. Egeland says Corsia’s effectiveness will “ultimately depend on the quality of carbon offsets that ICAO will accept”.
ICAO is also in discussions over a long-term climate goal for aviation for 2050, but it is not clear when this will be agreed or what the target will be.
Meanwhile, policies are being increasingly discussed at the national and regional level. In particular, the EU’s proposed “Fit for 55” climate legislation includes plans to mandate targets for SAFs and to end aviation’s fuel tax exemption. “Aviation fuel is exempt from any taxes almost everywhere,” says Grebenjak. “The EU wants to end the basically free rider status of aviation, and implement a kerosene tax that’s at the same level as other fuels.”
Chances of being solved? ICAO has been notoriously slow to act on aviation emissions, and many environmental groups criticise CORSIA for being far too weak, but recent policy moves at the EU level represent a significant step change.
5. The new middle class problem
Action at the EU level is encouraging, and the UK government even has a consultation out on its strategy for net zero aviation. However, the biggest growth in flying in the coming decades is expected outside Europe and the US, especially among the growing middle classes of developing countries.
Asia and the Pacific, Africa and the Middle East are the regions expected to see the most growth in the next 20 years, and last year China overtook the US as the world’s largest air passenger market. “The rise of a travelling middle-class in China and India has seen passenger demand grow at around 10% per annum,” says Hewitt.
Rutherford adds that frequent flyers look similar wherever in the world they are, namely upper-middle-class professionals. A global frequent flyer levy could therefore be one way to curb the growth, he says.
Chinese airlines will also increasingly have to meet local rules designed for climate mitigation if they want access to international airports, says Hewitt. But the vast majority of flights in China take place within its borders, which international policies would not apply to. “States will need to take domestic action to supplement international agreements in order to achieve net zero for aviation by 2050,” says Hewitt.
It’s worth noting that China also has the world’s largest high-speed rail network by far, while some developed countries, such as the US, have yet to install a single high-speed rail line. “We have to do our own homework first before talking about China,” says Grebenjak.
Chances of being solved? It’s up to developed countries to lead the way on reducing aviation emissions, which will then give more leeway to put pressure on developing countries.
6. The supersonic problem
Even amid growing efforts to reconcile aviation with a net zero world, some companies are pushing to develop aircraft that are even more polluting.
Earlier this year, United Airlines announced plans to buy 15 supersonic aircraft from Boom Supersonic, with the aim to begin using them by 2029. Rolls-Royce and the US air force also have deals with Boom.
As well as the noise issues with supersonics, these super-fast flights could consume five to seven times as much fuel for each passenger as subsonic aircrafts. There’s also a concern that supersonics, which will be operating high in the stratosphere, will have a disproportionate impact through non-CO2 emissions, says Rutherford. Developing emissions-intensive supersonic planes could also end up being a distraction from zero emission technologies such as hydrogen planes, he adds.
Rutherford says the best way to prevent climate damage from supersonic aircraft may be to require them to meet the same environmental standards as other airplanes. “That would, in essence, act like a ban,” he says. “They just can’t meet those standards.”
