​​​​​​​Hot topic: are we on our way to zero-emission flying?

Have the latest innovations in aviation fuel, electric batteries and hydrogen-powered aircraft led us one step closer to taking to the skies sustainably?

Despite accounting for just over 2% of the world’s greenhouse gas emissions, the aviation industry — almost exclusively dependent on fossil fuel — is seen as the poster child for global warming.

Photograph by Getty Images
By Graeme Paton
Published 6 Nov 2021, 06:00 GMT, Updated 23 Nov 2021, 11:13 GMT

From the heavy whiff of kerosene to the roar of jet engines and the criss-crossing of contrails, the recent return of commercial flights to our skies is an all-too-familiar attack on the senses. How aircraft will look, sound and even smell in another 30 years is altogether less certain. Despite accounting for just over 2% of the world’s greenhouse gas emissions, the aviation industry — almost exclusively dependent on fossil fuel — is seen as the poster child for global warming. Two years ago, the UK became the first major world economy to introduce a legally binding target to end its contribution to global warming, promising to achieve ‘net zero’ emissions by 2050 across every sector of the economy, from housing to energy, business to transport. However, it won’t be easy for airlines. Put simply, nothing else currently propels a plane as efficiently and cheaply as kerosene. 

What’s the future of ‘green’ air travel?

In the short-term, the focus will be placed on the fuel rather than the plane. Airlines are investing heavily in ‘sustainable aviation fuel’ — kerosene mixed with renewables and waste — to cut levels of carbon dioxide (CO2). In September 2021, British Airways operated its first flight between Heathrow and Glasgow using fuel from recycled waste cooking oil, cutting overall CO2 by 28%.

But a much more radical solution is needed in the long term.

Several companies have been pinning their hopes on battery power. As recently as 2018, EasyJet claimed it would be flying full-sized battery-electric planes by the end of the 2020s. However, there are serious doubts that large-scale pure electric flights will be feasible for decades, if ever, because of the size and weight of batteries required to generate the necessary thrust. In recent years, therefore, the focus has increasingly switched to hydrogen as a more efficient alternative.

Which carriers are at the forefront?

Hydrogen packs a huge amount of energy — three times that of kerosene and more than 100 times that of lithium-ion batteries — while producing zero CO2 from the engine and less noise. The problem facing airlines is making it commercially viable. In the UK, development of the technology has been led by ZeroAvia, a US-UK start-up. In September 2020, it operated the world’s most advanced hydrogen-powered flight. The company, backed by a £12.3 million UK government grant, tested its hydrogen fuel cell system in an adapted six-seat Piper M350 light aircraft on a 19-mile flight from Cranfield airport in Bedfordshire. Hydrogen is fed into the fuel cell and a chemical reaction generates electrical energy which, in turn, powers the motors, with only water vapour released.

The company is now preparing for the next stage, when it will develop a hydrogen-electric propulsion system that can power a far larger 19-seater. BA is among the airlines investing in the company.

Airbus, the European aviation giant, is also developing its own hydrogen-powered aircraft, the ZEROe, which will use liquid hydrogen as a fuel. Three design concepts have been drawn up, with backing from airlines such as EasyJet.

When will we be buying a ticket on a zero-emission plane?

It’s possible that zero-emission flights will be a reality for very short routes within three years. Loganair, which operates between the Scottish islands, is part of a UK government-backed consortium, Project Fesson, to develop a hydrogen fuel cell-powered plane, which could enter service by 2024. It is doubtful, however, that a large hydrogen aircraft — carrying 100 passengers plus — on longer routes will be possible until well into the 2030s. The Airbus ZEROe project is unlikely to produce results until 2035 at the earliest, mainly because the fuel cell and surrounding components are heavy and complex, while the hydrogen itself requires bulky storage tanks. This is relatively straightforward on short flights but can cause a major logistical challenge for larger commercial aircraft where more hydrogen is needed.

Will the price of air travel be cheaper?

The move to hydrogen — or ultimately battery power — should, in time, produce cheaper and quieter aircraft. Estimates suggest that hydrogen planes will be around a third cheaper to operate than kerosene aircraft because of the density of the fuel combined with the fact that they have far fewer moving parts, cutting down on costly maintenance. However, it will take time for these savings to be passed on to the customer. In the short term, the huge price of developing the technology, rather than relying on decades-old jet engines, will probably lead to higher initial costs.

Will planes of the future be truly ‘zero-emission’?

Potentially, yes, but there are significant hurdles to overcome. Aircraft production, like most manufacturing, is hugely carbon-intensive. Last year, Boeing claimed it had achieved ‘net zero’ in its worksites but only by offsetting some of its emissions, a practice condemned as ‘greenwashing’ by Greenpeace. Additionally, most of the world’s hydrogen, which will be needed to propel future aircraft, is produced by reforming methane from natural gas, a fossil fuel, which produces CO2. Efforts are underway to develop ‘green hydrogen’ using an electric current from a renewable source to convert water into oxygen and hydrogen, but the technology is still largely in its infancy.

In numbers...

1.1 billion tons
The annual CO2 emissions produced by global aviation — 2.5% of the world’s total (pre-pandemic).

The rise in CO2 emissions from aviation between 2013 and 2018 caused by increased flights, despite more efficient aircraft.

53 tons
The amount of CO2 produced by a flight from London to New York.

0.33 tons
The CO2 equivalent produced by one economy class passenger on a London to New York flight, rising to 0.6 tons in premium.

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