After almost a decade of negotiations, the International Civil Aviation Organisation (ICAO) has finally agreed a target for the industry to become net zero by 2050. Aviation has long been seen as lagging on climate action. In part this was because of the cross-border nature of air travel that makes agreement difficult and in part because of the physics of air travel. There are very few low-carbon options that offer the energy density of kerosene, making it much more difficult to decarbonise flights than other forms of travel.
So, what are the key ways to decarbonise aviation?
Batteries can power smaller aircraft but, currently, those with sufficient power to propel larger aircraft are too heavy to get planes off the ground, or at least to do so and travel any distance.
NASA has recently announced a new solid-state battery that could open up an era of electric aviation. Solid-state batteries are lighter than traditional lithium-ion devices, hold more energy and are safer. Until now, though, solid-state batteries have been unable to discharge energy fast enough for transport applications. However, NASA researchers believe they have solved that problem and that they could, in time, create more powerful, lighter batteries that could power longer flights and larger aircraft.
Hydro-jet by 2035?
UK based discount airline EasyJet plans to be flying short haul routes using low-carbon aircraft by 2030. Its initial focus was on electric aircraft, but it is also exploring hydrogen-powered flight. A growing number of companies throughout the aviation value chain, from Airbus and Boeing to start-ups such as ZeroAvia, are working on hydrogen aircraft, with the EU saying that the first commercial versions could enter the European market by 2035.
This would require not just significant changes to aircraft engines, and ultimately aircraft design, but also the creation of a low-carbon hydrogen infrastructure to manufacture the gas, which produces only water when it is used in a fuel cell or as a jet fuel in its own right. This hydrogen economy is being scaled up rapidly, but from almost nothing, meaning that it will, in reality, be more than a decade before there is enough hydrogen for flights to become a reality. Significant advances in hydrogen storage technology are also needed.
The EU says that hydrogen could feasibly power a commercial passenger aircraft on a flight of up to 3,000 kilometres by 2035, meaning that virtually all European routes could be hydrogen-powered. By 2040 or beyond, a medium-range flight of up to 7,000 kilometres should be possible, leaving just the very longest flights to be powered by fossil fuels. In the US, American Airlines has just announced an investment in Universal Hydrogen, a company building a green hydrogen distribution and logistics network for aviation.
The industry is also seeking to scale up the use of “sustainable aviation fuels” (SAFs). These can be made from 100% renewable waste and residue, raw materials such as used cooking oil and agricultural waste. Another possible route to scaling up SAF production is to make it from CO2 emissions captured either from industrial facilities or directly from the atmosphere.
These fuels have the advantage of being a direct replacement, or drop-in, for existing jet fuel, meaning that the industry does not need to introduce new fuelling infrastructure or change existing engines and fuselages.
SAFs cut emissions by up to 80% compared to fossil jet fuel over the fuel’s life cycle, according to Neste, a Finnish SAF producer. They are also free of sulphur, oxygen and aromatics, which combined with their high energy content, means that they burn cleaner in aircraft engines.
But while more than 450,000 flights have taken to the skies using SAF and over 100m litres of SAF were produced in 2021, this is still a drop in the ocean compared to the total amount of jet fuel consumed around the world – 432bn billion litres in 2019.
However you make it, SAF is currently about three times the price of kerosene, although recent energy price rises are narrowing that gap. Yet, because SAFs are a direct replacement for existing fuel, it can start to make an impact immediately by being blended with jet fuel to reduce its carbon content, with that proportion increasing as more SAF becomes available. By contrast, hydrogen or batteries are an all-or-nothing replacement.
There are also opportunities to cut emissions by optimising route management and landing approaches, phasing out fossil fuels for ground vehicles at airports and a range of other options. Singapore Airlines, for example, has just announced that it has adopted a tool that helps to optimise fuel use when airlines are climbing after take-off. The tool will cut the airline’s emissions by up to 15,000 tonnes a year.
The battle to cut aviation emissions is just beginning and it will be fought on multiple fronts.