By Katherine Tu
Global Aviation Emissions on the Rise
In 20 years, the demand for flying has quadrupled, with passengers traveling a total of 2 trillion kilometers in 1990 to 8 trillion kilometers (~5 trillion miles) in 2019, about the same as a light year. However, while energy efficiency has doubled, the carbon intensity of the fuel has not changed, resulting in a twofold increase in carbon emissions. The world now emits over 1 billion tons of CO2 from aviation (passenger and freight combined), an exponential jump from practically no emissions less than a century ago.
Source: Hannah Ritchie, Our World in Data, What share of global CO₂ emissions come from aviation?
Today, aviation accounts for 2.5 percent of the global emissions, and contributes around 4 percent to global warming when the non-CO2 emissions, such as water vapor, are included. That is roughly equal to the emissions of Russia in 2022, which is the 4th largest emitter in the world by country. However, only 2-4 percent of the global population flew internationally in 2018, and merely 11 percent of the world travelled by air (although the data is slightly dated, COVID had slowed down traveling and from 2019-2021, so it is a reasonable estimate for today). As income level and accessibility of air travel increase, global passenger traffic is projected to double by 2042, compared to 2024 levels. If our approach to flying remains the same, our global emissions from commercial flying could triple by 2050, reaching 1800 MtCO2/year based on ICAO (International Civil Aviation Organization) projections.
Sustainable Aviation Fuel (SAF) as a Solution
To address the high carbon intensity of aviation fuels, a cleaner alternative is needed. While EVs and hydrogen are the leading technologies for land transportation, SAF, a type of biofuel, is the biggest hope for the air.
There are 9 certified pathways in the production of SAF, involving various feedstocks such as biomass (agroforestry waste, non-food crops, algae, etc.), waste fats and oils, municipal solid wastes, and even direct capture of carbon dioxide from the air. To avoid emissions from land use change, such as deforestation, the biomass used must not be obtained from land converted from high carbon stock areas (primarily forests, wetlands, peatlands) after January 1st of 2008 to qualify for a CORSIA eligible fuel, which is an internationally recognized standard for SAF.
As shown in the figure above, the GHG emissions across the various SAF production methods and feedstocks are universally lower than the petroleum jet fuel baseline of 89 gCO2e/MJ across the lifecycle. This is thanks to the nature of using bio-feedstocks, where the GHG released during combustion is cancelled out by the carbon captured during their growth, essentially reaching net-zero combustion. The only exception is due to having a 40 percent mix of non-biogenic carbon in its municipal solid waste feedstock, resulting in a red bar showing combustion. Since combustion occupies 83% of lifecycle emissions in petroleum fuels, being able to avoid these emissions is the main driver of making SAF a viable clean alternative.
On the other hand, unlike other alternative fuels like electric or hydrogen, SAF also has the advantage of being readily integrable with existing systems. Its hydrocarbon composition is equivalent to the fossil Jet A fuels, which means that it can be safely blended with traditional fuels and used through the same pipes and engines. Although the current technology only supports SAF blends in 10% and 50% mixes, a 100% SAF will have the potential to reduce 94% of GHG emissions compared to conventional jet fuel. The International Airline Transport Association (IATA), therefore, estimates that 65% of the carbon reduction would come from SAF to reach net-zero across the aviation industry in 2050, calling for a push in policy incentives for scaled-up, innovative production.
Source: IATA, Developing Sustainable Aviation Fuel
Where is SAF Going in the US?
To meet the net-zero goal in 2050, global SAF use in aviation needs to exceed 10% by 2030, but the existing and planned projects can only supply 2-4% of fuel demands by 2030. As the United States holds the highest emissions in passenger and freight flights globally, the country must lead the way in decarbonizing aircraft to reach the net-zero goal.
In 2021, the Biden Administration announced the SAF Grand Challenge, which is a combined Memorandum of Understanding (MoU) of the Department of Energy, Department of Transportation, and Department of Agriculture to scale up technologies to increase SAF production. Specifically, they aimed to achieve:
- A minimum of a 50% reduction in life cycle emissions compared to conventional fuel
- 3 billion gallons per year of domestic SAF by 2030
- 35 billion gallons of SAF to satisfy 100% of domestic demand by 2050
According to its mid-2024 tracker, there has been considerable success, as the U.S. domestic production has increased from 5 million gallons/year in 2021 to 26 million gallons/year in 2023, importing 93 million gallons in 2024, which reduced approximately 200,000 metric tons of CO2e.
Meanwhile, under the Inflation Reduction Act, producers of SAF are given a $1.25 per gallon tax credit for fuels that reduce GHG emissions by 50%, while an additional $0.01 is awarded for each additional percentage that is reduced. As this bill expired at the end of 2024, it is interesting to see that the most recently passed “One Big Beautiful Bill Act” also included a “Clean Fuel Production Credit (45Z)” that provides $0.35 per gallon for SAF producers.
The Trump Administration has also approved a $782 million loan to the Montana Renewables Refinery in February, one of the few domestic SAF production facilities in the United States, allowing it to expand its production capacity from 140 million gallons to 315 million gallons. It seems like, despite the administration’s general skepticism toward climate policy, sustainable aviation fuel (or “synthetic aviation fuel”, as updated recently) still aligns with the energy independence goal.
Challenges Ahead
Despite its generally optimistic outlook, SAF still faces many challenges as it scales. First, it is rather costly to produce, as it remains 2-3 times pricier than traditional fuel. This may be passed on to the customers, and alter their support for the transition. Meanwhile, it takes time to establish the necessary supply chain and infrastructure for refinery, blending, and logistics, which may add to the production costs. As production scales, the current waste-based feedstock may be insufficient, and concerns arise about potential competition with food crops or land-use changes that could lead to undesirable consequences.
Although there are many considerations, there is no time for hesitation. Governments and businesses must collaborate to find solutions that make flying safer, more affordable, and more environmentally friendly for everyone.
Question for Readers
- What do you think about sustainable aviation fuel as an alternative? Do you think it’s a growing and profitable business, and do you think it will grow globally?
- What are some things we can do as passengers to help reduce emissions from flying?