A new study in the peer-reviewed scientific journal Nature highlights plausible pathways to net-zero emissions aviation, including the relative potential and trade-offs of changes in behaviour, technology, energy sources and carbon equivalent removals.
According to the IEA, in 2019, aviation accounted for 1.03GtCO2, or 3.1% of total global CO2 emissions from fossil fuel combustion.
The report explains that recent analyses have evaluated the technological potential of powering aircraft with sustainable aviation fuels (SAFs), hydrogen or electricity and offsetting aviation emissions by removing equivalent quantities of CO2 from the atmosphere.
SAFs include biofuels and synthetic fuels that are ‘drop-in’ replacements for jet fuel (that is, they would require little or no changes to existing aircraft and fuelling infrastructure) that meet ICAO’s sustainability criteria a net greenhouse gas emissions reduction on a life-cycle basis of at least 10% compared to fossil jet fuel, respecting biodiversity and contributing to local social and economic development.
One of the conclusions from the study is that “further reductions will depend on replacing fossil jet fuel with large quantities of net-zero emissions”.
SAF is considered the most important way to decarbonise airline operations in the next few decades, before alternatively powered aircraft can be widely deployed in commercial operations.
Compared to conventional jet fuel, SAF can reduce up to 100% carbon emissions on a lifecycle basis, depending on the SAF technology used. Aircraft today are powered by liquid aviation fuel, made mostly from fossil fuel sources. Yet new fuels have been developed that have the potential to dramatically reduce aviation’s net CO2 emissions. Although supply is currently limited (0.01% of global jet fuel use), sustainable aviation fuels (SAF) are already in use today and take-up is increasing.
With aviation currently accounting for approximately 3% of manmade global carbon emissions, the sector could end up consuming up to 22% of the global carbon budget by 2050 without significant action. To maintain growth and at the same time address its environmental impact, the wider aviation industry has committed to reducing net aviation carbon emissions to 50% below 2005 levels by 2050. Of all commitments by the sector, most prominently, the International Air Transport Association (IATA) committed in 2021 that emissions from global aviation would be net-zero by 2050.
Sustainable Aviation Fuel is a clean substitute for fossil jet fuels. Rather than being refined from petroleum, SAF is produced from sustainable resources such as waste oils from a biological origin, or non-fossil CO2. It is a so-called drop-in fuel, which means that it can be blended with fossil jet fuel and that the blended fuel requires no special infrastructure or equipment changes. It has the same characteristics and meets the same specifications as fossil jet fuel.
Since the first commercial flight operated by KLM in 2011, more than 150,000 flights were powered by SAF. Commercial aviation currently accounts for approximately 2-3% of manmade global carbon emissions, but without action, aviation could consume up to 22% of the global carbon budget by 2050.
More than 99% of airline emissions and approximately 50% of airport emissions are related to the combustion of jet fuel. Although increased energy efficiency and reduction in energy demand are effective ways to reduce fuel consumption and related greenhouse gas emissions, these improvements do not offer a sole solution to aviation-related emissions.
The aviation industry has a clear vision for its use of SAFs and will adopt only fuels made from feedstocks that can be grown or produced without the risk of unintended environmental and social consequences, such as competition with food production or deforestation.
Several airlines are driving forward the use of SAFs by signing multi-million dollar forward purchasing agreements. Others have invested in start-up support for SAF deployment, and some have promoted SAFs through test flights, research, and investigation of local opportunities. Five airports also have a regular SAF supply: San Francisco, Los Angeles, Oslo, Bergen, and Stockholm.
However, scaling up the use of SAFs to a global market is challenging and requires substantial investment. The industry has called on governments to assist potential SAF suppliers to develop the necessary feedstock and refining systems – at least until the fledgling industry has achieved the necessary critical mass and prices drop thanks to economies of scale.
SAF remains expensive, however – and high costs make fuel switching the most difficult in developing regions, where aviation demand is growing the fastest. Projected decreases in the costs of electrolytic hydrogen and captured carbon would make synthetic fuels more affordable, and higher conversion efficiencies and lower feedstock costs would help more airlines make the switch.
More than 45 airlines, including Qatar Airways, British Airways, Iberia, American Airlines, and Qantas now have commitments with SAF, or direct experience with SAF, and over 14bn litres of SAF are in forward purchase agreements.
  • The author is an aviation analyst. Twitter handle: @AlexInAir