The aviation industry needs a drastic reduction in its carbon dioxide emissions – and fast. At present, aviation accounts for 2% of all global energy-related CO2 emissions. Even with efficiency improvements, emissions are set to triple by 2050 on current growth projections.

Innovators are developing aircraft powered by electricity or hydrogen, but there are considerable challenges. Even on the most optimistic timescale, these challenges will not be overcome soon enough to achieve the carbon emission reduction required to achieve ‘Jet Zero’ by 2050.

Sustainable aviation fuels (SAF) offer a low-carbon option that could be scaled up faster than alternative engine types. However, it is not clear if even SAF will be sufficient to achieve the required reduction in aviation emissions.

The impact of aviation emissions

Around 70% of the exhaust gas from an aircraft burning conventional fuel is CO2. This greenhouse gas is emitted at around 3.16kg CO2 for every 1 kg of fuel consumed. CO2 stays in the atmosphere for a prolonged period – around 30% is gone in 30 years, 50% stays for a few hundred years and 20% will remain in the atmosphere for thousands of years.

Reducing the level of carbon dioxide released into the atmosphere is a clear priority for addressing climate change. However, opinions differ about other impacts of aviation emissions. 

Some scientists claim aviation has other non-carbon dioxide-related impacts on climate. These include complex chemical reactions of nitrous oxides released at high altitudes, as well as condensation trails forming cirrus clouds that contribute to the warming effect. If these additional effects contributing to climate change need to be factored into solutions then sustainable aviation will be considerably harder to achieve.

A critical timescale

There is an urgent need to reduce emissions from aviation. The problem is that it’s a heavily-regulated industry where innovation is complex and expensive.

Many see hydrogen or battery-fuelled aircraft as a solution. This is an area of intensive research, but it is estimated that 2040 is the earliest alternative engine types such as hydrogen or battery-powered engines could start to replace older conventional passenger jets. This is important as 95% of aviation emissions come from aircraft with 100 or more seats. While progress has been made in these engine types, this has focused on smaller or short haul aircraft.

It will simply take too long to design alternative engines, scale up production and replace older jets in the global fleet – even without factoring in the cost. And, by 2040, it is projected that increases in air traffic mean that the aviation industry will be responsible for 40% more emissions than today.

There simply isn’t time to defer change in the industry until hydrogen or battery powered aircraft become feasible at scale. SAFs will need to be used in the interim.

The potential offered by biofuels

Sustainable fuel must have a lower carbon footprint than conventional fuel, but this is only one element. To meet industry needs, SAF should also be suited to production and distribution at scale for roughly the same cost as traditional fuel. It also has to be compatible with current infrastructure and air fleets. Biofuels currently look like the best interim solution.

It is estimated that the industry could reduce 80% of carbon emissions by 2050 by using biofuels and rethinking jet engine design. Biofuels alone can achieve up to 83% reduction in carbon emissions generated by traditional aviation fuel, while also delivering 50-70% reduced ice crystal contrails.

The barriers to using SAFs

Sustainability is also about more than carbon footprint; SAF need to be sustainable in the sense of having minimal negative impacts on people and the environment.

Currently, the total global crop yield currently used for biofuels could produce calories to feed 1.9 billion people. With climate change and the war in Ukraine putting pressure on the food system, it becomes harder to justify producing biofuel crops on land that could be used for food production. Growing biofuels can also create competition in feedstock markets, pushing up costs for farmers and increasing food prices.

Biofuels also require water, land and fertiliser to grow, increasing pressure on natural resources and potentially contributing to deforestation and pollution. Biofuel production may also require fossil fuels through use of farm machinery, transportation and processing equipment.

What progress has been made?

Change is taking place in the aviation industry. In the US plans are in place to increase SAF production to 3 billion gallons by 2030, up from 60 million in 2022. The pressure to find solutions is also supporting innovation in the sector, with start-ups and research programmes shaking up a sector where change has traditionally taken a much slower pace.

For example, a major initiative from the World Economic Forum and Airports Council International is setting out to overhaul airports to support Jet Zero. Airports of Tomorrow will involve adapting airports for hydrogen and battery electric flight, use of SAF and electrification of airport operations.

As with any fast-developing area, standards have a crucial role to play. They can provide a common vocabulary to facilitate collaboration, offer guidance on best practice, support legislation and regulation, and help to create a level playing field for newcomers to the market.

Particular standards that may be of interest include:

• PAS 2060 Specification for the demonstration of carbon neutrality

• BS EN ISO 14064-1 Greenhouse gases – Specification with guidance at the organization level for quantification and reporting of greenhouse gas emissions and removals

• BS EN ISO 17225-1 Solid biofuels – Fuel specifications and classes – Part 1: General requirements

While battery or hydrogen powered aircraft may still represent the long-term future of sustainable air travel, the technology won’t reach most commercial flights any time soon. SAFs could well present the clearest immediate route to low carbon flight, and standards can help us get there.

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