Policy Watch: From contrails to e-fuels, how a UK-led coalition is helping plot a flightpath to greener aviation

Source: By Angeli Mehta, Reuters • Posted: Tuesday, July 9, 2024

July 8 – Speed is of the essence. The world has a very short space of time to decarbonise and, while there’s no shortage of innovation, promising technologies have yet to scale. How do policymakers decide which levers to pull to incentivise innovation and investment, while avoiding the sort of unintended consequences that accompanied an early push for biofuels? And how can they be encouraged to move swiftly?

Aviation is a good example of the challenge. The industry is responsible for more than 2% of global carbon dioxide emissions, but once non-CO2 emissions are considered the figure could be at least twice as high.

No one knows what its decarbonised future will look like. Sustainable aviation fuel (SAF), hydrogen or battery electric could all play a role, but how much will depend on factors such as the speed of grid decarbonisation, competition for feedstock from other sectors (for example, shipping) and new battery chemistries.

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In 2020 Professor Rob Miller, director of the Whittle Laboratory at the University of Cambridge, was involved in a series of aviation workshops organised by the then Prince of Wales, through his Sustainable Markets Initiative. All the relevant players were in the room, from technology experts to air traffic controllers and airport operators.

“What we realised in those meetings was that people were talking past each other; there was no common language,” says Miller. The field of aviation had “become very siloed … nobody saw the whole picture anymore.”

Having pioneered rapid technology teams to shrink research and development times in the aerospace sector from years to months, Miller’s group wondered if the same approach could work here, building across boundaries to develop a common language that could enable better and faster decision-making. The Aviation Impact Accelerator was born, led by the Whittle Laboratory and the Cambridge Institute for Sustainability Leadership.
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At the Whittle, named for the inventor of the jet engine, they set about building a model covering the whole picture of potential aviation decarbonisation pathways taking account of all the resources required – from land, water and finance, to distribution networks and the transition requirements of other sectors – to assess the climate impacts of different technologies, fuels and policies. The model also makes clear where the uncertainties lie.

There’s now a suite of linked models that can be tailored for different audiences, opening up a new interface between science and policymakers. For example, one tool helped the UK government develop its sustainable aviation fuel mandate, which set a target of 10% of all fuel in flights leaving the UK to come from sustainable sources by 2030.

The whole system is a result of partnerships with universities and companies around the globe, from disciplines as diverse as propulsion technology, philosophy and sustainability. That expert knowledge is essential, notes Miller, because “one technology shift can change the whole playing field”.

When policymakers road-tested the model at an international workshop in the United States early last year, Miller says they discovered “we have this sudden moment where there are bifurcations or tipping points. So, there are actions that as a policymaker you could put in place in the next five years, which totally change the future.”

That’s critical, says Miller, because current transition mapping suggests a linear pathway to multiple technologies in 2050.

“If you looked at cars in the early 2000s, people were all working on biofuels. They were absolutely convinced there was a wedge chart of biofuels that went to 2050 and was going to be the answer. Then Tesla came along and changed everything. We are not at that moment in aviation. We’re either going to run on SAF into the long term, or we’re going to have a ‘Tesla moment’ and there’s going to be hydrogen or another technology that will come in and cause the transition.”

So what options does the sector have to decarbonise? The Aviation Impact Accelerator has international teams working on fuels, technology, energy efficiency and non-CO2 impacts such as contrails. Later this month they’ll report on their detailed findings.

Contrails, the white trails of cloud that some planes leave in their wake, is one area of great uncertainty. Whether or not they form depends on atmospheric conditions, and they can reflect sunlight back into space as well as trapping outgoing radiation as heat. Miller explains that fewer than one in 30 flights causes the bulk of the warming attributed to contrails and, although they disappear within 24 hours, their warming impact over 50 years is thought to be as great as the CO2 emissions of all 30 flights.

Last year, Google and Breakthrough Energies teamed up with American Airlines to demonstrate that using artificial intelligence to predict when contrails are likely to form could help pilots avoid those altitudes. . They reported a 54% reduction in contrail formation, for just an additional 2% fuel burn.

The Cambridge team is advocating setting up living flight labs in a controlled area of airspace, such as the North Atlantic, to learn the best approaches to contrail avoidance before legislation is put in place.

Focusing on energy efficiency is also crucial: big gains could be made by designing aircraft better-suited to the distances they travel, so that a plane built for a transatlantic voyage isn’t flying between European cities. Breaking up long-haul flights into two shorter hops is also beneficial.

Miller estimates that pulling all levers to the full could reduce the expected fuel burn from aviation in 2050 by about half, compared with business as usual. That’s a big intervention since the expected growth in aviation suggests a doubling of today’s fuel consumption by 2050.

The aviation sector has yet to work out which fuel or technology options can replace fossil kerosene. Plants to make SAF are being built – although at a fraction of the rate industry requires – and governments, including the UK, EU and Japan, have set SAF mandates.
At present, most SAFs are being made from used cooking oils. But, as many observers have pointed out, they can only meet a fraction of the industry’s requirements, with the potential for fraud as demand outstrips supply. SAFs can also be made from biomass waste but again, supply is limited.

So-called power-to-liquid, or e-fuels, are promising. Here green hydrogen, made using renewable electricity, is combined with carbon dioxide captured from the atmosphere using a well-established chemical process that converts the ingredients into liquid hydrocarbons. Neither biomass nor e-fuels eliminate carbon dioxide but could cut well-to-wheel emissions by up to 90%.

Meeting all the sector’s current demand with e-fuels would require 40% of today’s global electricity production, but expected demand could see that double to 80% (of today’s output) by 2050. Waste biomass alone can’t meet the industry’s demand, but there is a third way, Miller explains. Combining the two technologies reduces the energy required to produce fuel and uses the carbon contained in biomass to the full. “It’s a push, but it is doable,” he suggests.

A team is also exploring hydrogen propulsion, working with Rolls-Royce on a new jet engine powered by liquid hydrogen. This could cut the energy required by up to 20%. While the volume of liquid hydrogen is four times greater than that of kerosene, its weight per unit of energy (even including the weight of the fuel tanks) is half that of kerosene – an advantage that comes into its own for very long-range flights, where fuel weight at take-off is 40% of total weight.

“I don’t know what’s going to win, but the cost of demonstrating the technologies at scale are miniature compared to the costs of the total transition,” says Miller. “So, you want to be moving those demonstrators really early, with total focus. And at that point, you’ll be able to decide whether the future is hydrogen or not.”

Aviation doesn’t sit in a vacuum. The next big change in SAF policy will be to consider how the transition will occur across different sectors, and their demands for hydrogen and electricity, for example. “We need to play all those scenarios out and make sure there are solutions which are robust to what other sectors do,” says Miller. That also requires international coordination.

The Sustainable Markets Initiative has set up working groups of chief executives from across the globe, to address some of the challenges that have been identified.

The Cambridge group is also in the process of setting up a land use accelerator, an idea that grew out of work on global biomass availability for SAFs. The new focus will consider implications for biodiversity and water use. Also in prototype are tools for the maritime sector.

The work of the Aviation Impact Accelerator has generated excitement on both sides of the Atlantic. Will policymakers the world over now seize on the tools they’re being offered to go for the moonshots that could get us over the line in 2050?