We found that as much as 19.8 exajoules of sustainable aviation fuels could be needed for the entire sector to reach net-zero CO₂ emissions. With other efficiency improvements, that could be reduced to as little as 3 exajoules. To put that into context, 3 exajoules is almost equivalent to all biofuels produced in 2019 and far surpasses the 0.005 exajoules of bio-based jet fuel produced in 2019. An exajoule is a measure of energy.

Flying less and improving airplanes’ energy efficiency, such as using more efficient “glide” landings that allow airlines to approach the airport with engines at near idle, can help reduce the amount of fuel needed. But even in our rosiest scenarios – where demand grows at 1% per year, compared to the historical average of 4% per year, and energy efficiency improves by 4% per year rather than 1% – aviation would still need about 3 exajoules of sustainable aviation fuels.

A rapid expansion in biofuel sustainable aviation fuels is easier said than done. It could require as much as 1.2 million square miles (300 million hectares) of dedicated land to grow corps to turn into fuel – roughly 19% of global cropland today.

Another challenge is cost. The global average price of fossil jet fuel is about about US$3 per gallon ($0.80 per liter), while the cost to produce bio-based jet fuels is often twice as much. The cheapest, HEFA, which uses fats, oils and greases, ranges in cost from $2.95 to $8.67 per gallon ($0.78 to $2.29 per liter), but it depends on the availability of waste oil.

Fischer-Tropsch biofuels, produced by a chemical reaction that converts carbon monoxide and hydrogen into liquid hydrocarbons, range from $3.79 to $8.71 per gallon ($1 to $2.30 per liter). And synthetic fuels are from $4.92 to $17.79 per gallon ($1.30 to $4.70 per liter).

Realistically, reaching net-zero emissions will likely also rely on carbon dioxide removal.

In a future with similar airline use as today, as much as 3.4 gigatons of carbon dioxide would have to be captured from the air and locked away – pumped underground, for example – for aviation to reach net-zero. That could cost trillions of dollars.

For these offsets to be effective, the carbon removal would also have to follow a robust eligibility criteria and be effectively permanent. This is not happening today in airline offsetting programs, where airlines are mostly buying cheap, nonpermanent offsets, such as those involving forest conservation and management projects.

Some caveats apply to our findings, which could increase the need for offsets even more.

Our assessment assumes sustainable aviation fuels to be net-zero carbon emissions. However, the feedstocks for these fuels currently have life-cycle emissions, including from fertilizer, farming and transportation. The American Society for Testing Materials also currently has a maximum blend limit: up to 50% sustainable fuels can be blended into conventional jet fuel for aviation in the U.S., though airlines have been testing 100% blends in Europe.

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