Can flying ever be sustainable?

When it comes to debate around sustainable travel, there is one sector that comes under particular scrutiny. Despite research (published in the Global Environmental Change Journal) stating just 11% of the world’s population travel by plane, and only 1% fly frequently, aviation currently accounts for around 2.5% of global carbon emissions. What’s more, it contributes to as much as 5% of climate change attributed to human activity. And as things stand, these figures are only set to rise.

At the current trajectory, emissions from commercial air travel have been predicted by the United Nations aviation body to triple by 2050. It is for this reason that many governments – including the UK – are investing in alternative fuels, in the hope of reducing carbon emissions and tackling this major contributor to climate change.
Biofuels, green hydrogen and synthetic e-fuels are just some of the substitutes being researched and tested as potential replacements for traditional jet fuel, but it’s currently ‘sustainable aviation fuel’ (SAF) that is getting the most attention.

What is SAF?

While traditional kerosene-based jet fuel derives from fossil fuels (primarily crude oil), SAF is typically created using waste oils (such as used cooking oil), animal fats and ethanol derived from corn production. Like traditional jet fuel it is a hydrocarbon, refined via a three-stage process, and produces a similar amount of CO2 when burned. So, where does the name come from?

The ‘sustainable’ tag arises from the life-cycle of SAF emissions, which considers its origin (from plants and livestock rather than fossil fuels) as well as its renewability. There are also significant practical benefits, in that the use of SAF requires little alteration to current aircraft and could, in theory, be introduced quickly and efficiently in a heavily diluted form. Current regulations only allow airlines to use up to a 50% blend of SAF and regular kerosene fuel without special permission.

Is SAF truly sustainable?

Unfortunately, SAF isn’t as ‘sustainable’ as its name makes out. A 2023 report by The Royal Society states that to meet the commercial aviation needs of the UK, more than half the country’s farmland would need to grow SAF-purposed crops. Even if this were possible, monoculture farming is a huge driver of deforestation, land degradation, freshwater pollution and biodiversity loss.

“Biofuels and SAF are simply not sustainable, as we need our crops for food,” explains Helena Bennett, head of climate policy at Green Alliance. “There are people living in poverty, so transforming land used for food crops into fuel crops isn’t tenable.”

Added to this is the fact that the majority of recycled oil stocks is currently used to reduce emissions in ground transportation. If it were to be primarily used in aviation, the scarcity elsewhere might push other industries into using less sustainable fuels.

It’s understandable why the airline industry wants to get behind SAF as an idea. The UK’s Advertising Standards Authority (ASA) recently pulled up airlines for promoting its use as a means of ‘protecting the environment’. But there are lots of issues to be addressed first.

One of the more concerning is that the CO2 emitted by aircraft in flight is not reduced by using SAF. “These emissions are also more potent than at surface level,” adds Helena. Indeed, CO2 has a larger heat-trapping effect in the cooler temperatures found in the upper atmosphere, and it is a problem for which there is no obvious solution.

The use of SAF also doesn’t change aircraft emissions of other greenhouse gases, such as nitrous oxide – which has a Global Warming Potential (GWP) 273 times that of CO2. However, studies carried out by NASA and the German Aerospace Center do suggest SAF use may at least produce fewer contrails (icy clouds formed from water vapour), which are a large contributor to aviation-induced warming – though this is still under investigation.

Investment and innovation

Last year, the British government proposed that SAF should be a major source of fuel in UK commercial aviation by 2030 – its Jet Zero strategy demands at least 10% of fuel used should be SAF. It also aims to build a minimum of five UK-based commercial SAF plants by 2025. The bare facts, however, are that even if production could be proportionately scaled, biofuels currently represent less than 0.1% of total jet fuel used today, so widespread use of 100% SAF would takes years to implement.

“The only way to build a fully zero-emissions flight is to create new ways to propel planes,” believes Helena. For many people, green hydrogen (made from water using renewable energy) looks to be the best future alternative, but even this would require huge supplies, airport infrastructure and for planes and engines to be redesigned, which is both a timely and expensive process.

What travellers need to know

We’re on an evolutionary journey with alternative fuels. SAF has gained traction because politicians and the industry are getting behind it, but the general scientific consensus is that it currently doesn’t have the potential to be a genuinely sustainable fuel source.

The good news is that there are scientists, engineers and experts working hard to build true zero-emissions flights, but they need government investment and industry support to make that happen in the next decade.

In the meantime, travel is a £6.07 trillion industry on which many nations depend, so the answer isn’t to travel less but to find alternatives to flight. Taking the train more regularly and embracing overland travel for short-haul trips are currently the most powerful ways to reduce your carbon footprint. It’s just one step in what will be a long journey for us all.

Case study

Virgin Atlantic flies on 100% SAF

In late November 2023, Virgin Atlantic became the first commercial airline to complete a long-haul flight from London Heathrow to New York JFK airport using 100% SAF.

At the time, Virgin Atlantic CEO Shai Weiss announced: “Flight100 proves that sustainable aviation fuel can be used as a safe, drop-in replacement for fossil-derived jet fuel and it’s the only viable solution for decarbonising long-haul aviation.”

However, as reports show, the availability of the feedstock from which SAF is derived is simply not at the levels needed for this alternative fuel to go mainstream. Transforming land used for food crops into fuel crops will only transfer the problem, putting pressure on the global food system and risking more environmental degradation.

What Flight100 does demonstrate is how innovative technology can be built – providing there’s large investment from both industry and government – and that gives us all hope for change.