Originally published on February 8th, 2020
Dear airlines, please sell us sustainable aviation fuels (SAF). It’s the only feasible way to green up aviation at the moment.* I’ve cleaned up most of my CO2-emitting activities, but now flying remains as the largest remaining slice of the pie. I have a family that is spread out over multiple continents and travel a decent amount for work, which usually involves flying. I’m not the only one in this situation: several others have simply decided to stop flying or shame those who do. I’m a strong believer that aviation is good for modern society: about a third of global trade by value is transported by air, and traveling to other places makes us more open and creative. As Mark Twain famously stated, “Travel is fatal to prejudice, bigotry, and narrow-mindedness.” With that said, I’d like to work with you to make aviation a better global citizen as we move into the next decade.
How should airlines address this?
What I’d like all of you to do is add an option in your booking flow to “fly my seat with sustainable fuel.” You’re clearly experts at upselling exit rows, early boarding, bags, and other things, so I know that building the web experience should be trivially simple for you. From a pricing standpoint, you can compute the marginal cost differential between SAF and fossil jet based on the route, the aircraft assigned, and historical fuel burn to spit out a number. Then we, the consumers, can simply select the option and be on our way. Microsoft has pledged to remove its historical CO2 and go CO2-neutral by 2030, so selling them the option should be a slam-dunk (Delta and Alaska, I’m looking at your corporate contract teams right now) (Edit: looks like KLM has part of the pie). More will surely follow. Some of you have already gotten started in the space, but if I didn’t proactively search for these resources, I wouldn’t find them. If the emergence of flygskam in 2019 is an indicator for the future, then you need to start skating to where the puck’s going by adding the SAF booking option for us. That cash flow will boost SAF investment to accelerate the closing of the cost gap to fossil jet. The IPCC tells us that we’ve got 10 years, so get to work.
*Why is SAF currently the only real option?
Right now, commercial aviation represents roughly 2% of global CO2 output, and that fraction is climbing. Aircraft efficiency has improved in leaps and bounds during the jet age and continues to improve about 10–15% with every new generation of airliners. These improvements in efficiency make it so much cheaper for people to fly that we are seeing overall passenger numbers climbing at 5% per annum while total emissions are climbing at 3%. By 2050, emissions are expected to be at triple their current amount. What we need is not just to reduce unit emissions (efficiency), but total emissions as well, and quickly.
Global agreements to limit emissions have not gone well, as evidenced by the squabbling over the ETS and the fizzled COP 25 summit. Most people think their governments are dysfunctional, so those waiting for a few hundred of those to cooperate must have a lifetime supply of popcorn.
What can be done to reduce emissions?
Several ideas have been proposed over the years to address aviation’s growing CO2 emissions. Pioneers in electric propulsion like Harbour Air have flown an e-Beaver using a magni-X motor, which will help improve air quality, reduce noise, and reduce maintenance costs. The problem with electric propulsion remains energy density: lithium-ion batteries have 2% the energy per unit weight as jet fuel. Factoring in better powertrain efficiency gets us closer to 7%. I’m excited to see the batteries improve, but it will likely be decades until a battery-powered plane can cross oceans with a useful payload at a reasonable cost. For longer distances, hydrocarbons are presently the only realistic energy source that can keep planes in the air.
CO2 offsets have been proposed as a solution, but many of them have their own problems: dig up fossil fuels from long-term storage, introduce it to the short-term carbon cycle by flying, and pay someone to plant a few trees to offset that. Seems great, but how can anyone be sure that those trees don’t get chopped down for firewood in a decade?
This leaves us with SAF as our only realistic option. Broadly speaking, SAF includes synthetic fuels made from renewable energy and second-generation biofuels that don’t compete with food production like first-gen biofuels. SAF, due to its production process, usually consist of fewer molecule types and fewer impurities than fossil jet, which results in cleaner combustion, 50–70% fewer particulates, and in turn fewer heat-trapping contrails.
Why are we not flying with 100% SAF yet? Two reasons: fuel composition requirements and cost. The fuel specification for Jet-A, ATSM D-7566, currently requires 50% petroleum-derived fuels to ensure sufficient aromatics in the blend to preserve engine seals. Many forms of SAF don’t have sufficient aromatic compounds, which can cause seal shrinkage. Some companies, like Byogy, have addressed the problem of the aromatics content, so the specification could be amended once adequate experience shows that the fuels perform similarly. Regarding the economics, SAF is currently more expensive than fossil jet fuel for a few reasons: