Green skies need more than decarbonisation
cessna 208 transparent.png
Dominic Weeks
April 24, 2022

This year will be a crucial one for the aviation industry. As recovery from the pandemic picks up pace, the industry must wrestle with supply chain and fuel effects caused by the deteriorating geopolitical situation. It will be hard, but essential, for the industry to focus on sustainability plans ahead of the ICAO general assembly later in the year.

The problem is not going away. While it represents around 2.4% of global carbon emissions (
ICCT) and 12% of transport’s contribution (ATAG), aviation has come to be the poster child for transport’s climate impact—hence the recent dictionary entry for flygskam.

It is not an unjustified focus. In line with passenger demand, the sector’s carbon emissions are predicted to sky-rocket. It is also one of the hardest sectors to decarbonise. So are governments’ visions of net zero aviation (or “jet zero” as the UK Government has termed it) realistic and, if so, are we on course?

There are significant reasons to be optimistic. Appetite in the industry to support technologies that can aid in reducing carbon emissions is pervasive, and airlines and airports alike are seriously considering their transition plans.

However, targeting just carbon emissions belies the fact that, when it comes to aviation, a much broader climate change challenge exists. New climate modelling techniques
suggest that total aviation emissions are warming the climate at about three times the rate of CO2 aviation emissions alone (EASA). Combustion, even of Sustainable Aviation Fuels (SAFs), creates nitrogen oxides (NOx), sulphur oxides (SOx) and other particulates like soot, and their release at altitude creates contrails. According to an EASA report, aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO2 emissions alone. Aviation’s climate impacts go far beyond just carbon emissions, not to mention the air quality impacts for communities living in and around busy airports.

While SAFs are rightly celebrated as a crucial bridge technology to curb carbon emissions on longer range flights in the short term, the downsides need to be articulated so that they are not seen as the long-term solution, hampering adoption of true zero emissions technologies. A drop-in fuel for existing aircraft engines, SAFs have both the blessing and the curse of convenience, but also the significant downside of combustion and the related non-carbon climate impacts.

Just as with road vehicles, electrification is the key to reducing global warming impact in aviation. The difference is that electrification need not mean only battery power. Battery electric will play a role for very small aircraft over short distances, such as air taxis, but unlike with electric vehicles, the power requirements for commercial aviation cannot be met by current battery technology due to poor energy-to-weight ratio.

Hydrogen-electric aviation, using fuel cells and electric motors in engines, can overcome this barrier. Hydrogen has over 100 times more energy per unit of mass than the best lithium-ion batteries today and hydrogen fuel cell technology utilised to propel aircraft emits only water vapour. If powered by green hydrogen, produced from renewable energy at airports, the system-wide greenhouse gas emissions impact is extremely limited.

Governments have been responding alongside industry to this opportunity. The UK Government last year published its
Hydrogen Strategy, setting out a framework for supporting the target of 5GW of low carbon hydrogen production and envisages aviation as a key end use case over the coming years, with airports acting as important hubs for hydrogen supply. It will later this year build on the success of the Jet Zero Council by releasing a Jet Zero Strategy.

Bill Gates’s Breakthrough Energy Ventures (an investor in ZeroAvia) last year announced a $1.5 billion public-private partnership with the U.S. Department of Energy to accelerate the adoption of next-generation clean energy technology including green hydrogen, building on a similar arrangement with the European Commission. The U.S. DOE is also busy building out its Office for Clean Energy Demonstrations to help with the rollout of the hydrogen hubs funded by the Infrastructure Investment and Jobs Act, or BIL (Bipartisan Infrastructure Law). 

This is encouraging as using green hydrogen in aviation is the furthest reaching solution, but still too much of the debate looks at decarbonisation in isolation.

Momentum is building around supporting a transition to green flight. It is crucial now that we set the long-term target at zero carbon while also looking at the non-carbon emission climate change impact of aviation.