Advanced BioFuels USA

by Candelaria Bergero and Steve Davis (The Conversation) … In a new study, we examined different options for aviation to reach net-zero emissions and assessed how air travel could continue without contributing to climate change.

The bottom line: Each pathway has important trade-offs and hurdles. Replacing fossil jet fuel with sustainable aviation fuels will be crucial, but the industry will still need to invest in direct-air carbon capture and storage to offset emissions that can’t be cut.

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We developed and analyzed nine scenarios spanning a range of projected passenger and freight demand, energy intensity and carbon intensity of aviation to explore how the industry might get to net-zero emissions by 2050.

 

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.

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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.

How to overcome the final hurdles

To meet the climate goals the world has set, emissions in all sectors must decrease – including aviation.  READ MORE