Airplanes provide transportation for people, goods, and more, connecting our economies and cultures. But flying is also one of the most carbon-polluting human activities contributing to climate change. A single passenger’s carbon footprint from a round-trip flight from New York City to London is higher than the annual CO2 emissions of the average person in 49 countries in the world, including Burundi and Nicaragua. According to the Environmental Protection Agency (EPA), aviation is the third largest source of US transportation greenhouse gas emissions annually, and overall the transportation sector is responsible for the largest portion of greenhouse gas emissions. Globally, the aviation sector accounts for 2% of CO2 emissions every year. However, it is worth noting that this impact is not distributed evenly among flyers. UK surveys in 2013 and 2014 found that 70% of annual flights were on account of 15% of the adult population, while a 2022 poll found that the average American had taken only 1.4 trips over the course of 12 months. Annually, the average amount of CO2 produced by the average person is 7 metric tonnes, versus a 3,300 average for celebrities and the wealthy. Private aircrafts are partly to blame for this disparity; in 2019, 10% of all departing flights from France were private planes. As the aviation industry continues to expand, with 8 billion passengers expected by 2050, solutions are direly needed for both the public and private sectors to reach the 2050 net zero goals set by the International Civil Aviation Organization (ICAO) in alignment with the Paris Agreement.

Accelerated development and widespread deployment of sustainable aviation fuels (SAFs) have  become an increasingly popular focus, as SAFs are projected to reduce emissions by up to 80% throughout their lifecycle when compared to petroleum-based jet fuels. SAFs are biofuels produced from renewable biomass and waste. In the US alone, enough biomass can be sustainably collected annually to produce 50-60 billion gallons of low-carbon fuels, more than enough to meet the demands of the national aviation industry. The International Air Transport Association (IATA) has estimated that switching to SAFs would cover 65% of the emissions reduction needed for  the global aviation industry to reach net zero by 2050. Additionally, SAF production from these renewable resources can provide benefits beyond lowering global greenhouse gas emissions, including enhancing aircraft performance, improving the environment, and creating extra revenue for farming communities. 

SAFs have been on the rise since the first test flight with biojet fuel was performed by Virgin Atlantic in 2008. As of 2022, SAFs have been used for 450,000 flights by more than 50 airlines, 300 million liters of SAFs are being produced annually, and around $17 billion of SAFs are in forward purchase agreements. Private aviation company Victor has partnered with SAF producer Neste to allow customers to purchase SAFs as a replacement for conventional jet fuels, already encouraging 20% of customers to book using this reduced carbon footprint. The SAF market is expected to see a 70-fold increase to $15.7 billion by 2030.

SAFs are presently used as blended fuels with conventional jet fuels, taking advantage of existing infrastructure and tampering costs. Currently, there are seven technological pathways to SAFs that have been approved by the American Society of Testing and Materials (ASTM) for blends containing up to 50% SAFs by volume. A summary of these pathways and their feedstocks can be found in the table below. 

table describing the 7 pathways to sustainable aviation fuels and their feedstocks, processes, maximum blend levels, and years of approval
The Seven Currently Approved Pathways to SAFs

Despite these technological developments in SAF production and accelerated usage, biofuel still makes up a small portion of the fuel used in the aviation industry that consumed over 360 billion liters of fuel in 2019 alone. There are currently only two companies that produce SAFs on a large scale used by major airlines, US company World Energy and Finnish Company Neste, although startup companies are beginning to break into this space such as Illinois-based Lanzajet and Colorado-based Gevo. Startup company Alder Fuels, in collaboration with the National Renewable Energy Laboratory (NREL), is developing a new pathway to SAFs, for which they received a Department of Energy (DOE) grant for a demo facility and are seeking ASTM approval. Analysis so far shows that this technology could produce fuels from wet waste with a negative carbon footprint and be used for high-volume fuel blends of up to 100%. Additionally, Air Company is another startup breaking into the SAF market with a SAF derived from carbon dioxide that has already been approved and flown by the US Air Force. Additional buyers already lined up include the jet maker Boom Supersonic and airlines JetBlue and Virgin Atlantic. 

Still, even the largest consumer of sustainable fuel in the US, United Airlines, only used SAFs for <1% of their total fuel consumption in 2022. This is in large part due to cost. Biofuels are currently triple the cost of conventional petroleum-derived fuels. Recent scientific advances and funding have focused on expanding available pathways to SAFs and lowering costs. For example, in 2021 the Biden Administration outlined a Sustainable Aviation Grand Challenge to produce 3 billion gallons of SAFs and reduce airplane emissions by 20% by 2030. Aligning with this goal, the US DOE Bioenergy Technologies Office (BETO) announced nearly $65 million in funding for projects to generate cost-effective, low-carbon biofuels. Most recently, in February 2023, United Airlines started a $100 million venture capital fund for SAF technology investments to support its goal of reaching net zero by 2050 without carbon offsets.

This growing momentum for decarbonizing the aviation sector is due in part to customer accountability and supportive policy innovations. For an industry wherein fuel accounts for 30% of expenses, the switch to SAFs for the aviation industry greatly benefits from public and government motivation. Along these lines, recent policies have focused on continuing to support this momentum for realizing sustainable aviation. Discussions concerning the need for higher blend limits are ongoing, as compatibility must be accessed. However, it has been proposed by scientists in a recent Environmental Science & Engineering article that using SAFs in higher blends for planes with higher emissions, rather than distributing them uniformly, would increase the climate benefits of SAFs by a factor of 9-15 — an attractive potential strategy if fuel supplies are constrained with increasing demands. The European Commission has proposed a SAF blending mandate of 63% by 2050 for fuel supplied to EU airports. Furthermore, with the Inflation Reduction Act of 2022, the Biden Administration passed tax credits for SAFs, and Canada recently implemented a 10% tax on luxury aircrafts.

Air travel has become crucial to the interconnected world in which we all live. Continued development and deployment of SAFs supported by governments, industry, and scientists shows promise for realizing the net zero goals that many have set for 2050 and reducing a significant source of CO2 emissions adversely affecting our climate. Let’s hope we keep this momentum up in the air with some lighter environmental baggage.


Peer Editors: Devan Shell and Sy’Keria Garrison

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