Can flying ever go green?

Define green.

Today I learned that United Airlines uses biofuels from municipal sewage for a portion of their jet fuel for flights out of LAX.  In 2016, they contracted to purchase up to 15 Million gallons of biofuel over 3 years.  At the end of the contract, they signed up to purchase up to 10 M gal/year, doubling their use.

In 2016, WaPost wrote that the biofuel would be blended in a mixture of 30 percent biofuel and 70 percent traditional fuel.

But the use of biofuels is one possibility for existing machines to cut down on their emissions without having to upgrade their engines or other aspects of their design or engineering. “Drop-in” fuels are renewable fuels that are designed to work safely with existing engines, although as in the case of the United flights, they sometimes require mixing with traditional fuels.

This is analogous to cars in California using a blend of 15% bioethanol and 85% gasoline. If the ethanol comes from grains like corn, then the carbon savings is minimal.  If the bioethanol and biomethane comes from food waste, then the payoff is bigger.

Putting it in perspective.  United Airlines used 4292 Million gallons of fuel in 2019, of which 5 M gal was biofuel.  Even if they were to double that to 10 M gal/year, that would be 0.2% of their fuel use.

So, biofuels in airplanes is better than diesel.  But it's even better if we cut down on our flying overall.  It doesn't have to be much.  Cut down on one round trip long haul flight per year and it's as much carbon savings as if you traded in your gasoline-powered car for an electric car.

I copied the figure from Quantifying the potential for climate change mitigation of consumption options, which I also wrote about in New Paper on Global Data-Driven Climate Actions.

We cut back on personal flights so that we make one long-haul trip every few years.  I was supposed to fly home from Germany yesterday-today.  Bad Dad was going to represent his family at the commemoration of the liberation of Bergen Belsen 75 years ago.  The ceremony will be postponed.

We don't fly long distances for short trips.  We make fewer, longer trips.  We had planned to spend 3 weeks, visiting Berlin, Munich and some smaller towns in between.  I even planned to show him the small town where I had been an exchange student in high school (German Gymnasium.)  It will have to wait.