Need to fly? Fly like a NERD!

In my last blog, I wrote about who flies, how that impacts the climate, and how we need to start thinking about curbing traffic growth in addition to accelerating investments in low-carbon technologies. But in countries like the United States, with its low population density, generally mobile population, and substantial immigrant population, it can be hard to work or visit family without flying. So, what can we do about the trips that can’t realistically be avoided?

This is a question I’ve grappled with myself, given that three-quarters of my direct energy CO2 footprint is linked to flying, overwhelmingly for work. There’s no doubt that flygskam, or flying shame, is legitimate. While aviation is only 2.4% of global CO2, that statistic hides the fact that only a small fraction of the world flies regularly. This means that most people don’t fly much, and that about two-thirds of all aviation emissions can be linked to a small number of frequent fliers.

Broadly speaking, your choices to reduce the climate impact of flying are to either 1) choose flights with higher fuel efficiency or 2) choose flights using fuels that produce less CO2 on a lifecycle basis when burned. (Note that I’m ignoring here strategies that might reduce the non-CO2 climate impacts of flying. That’s because there’s still scientific uncertainty about these impacts, and because in most cases those impacts will scale approximately with CO2 emissions.) Let’s consider fuels first.

Industry showcases its efforts to develop alternative jet fuels for aviation. Progress has indeed been made to certify fuel blends as safe for drop-in use, but the story pretty much stops there. According to the UN’s International Civil Aviation Organization, roughly 7 million liters of alternative jet fuel was produced in 2018. As illustrated in the figure below, this is dwarfed by the about 360 billion (with a “b”) liters of fossil jet fuel consumed that year. This means that enough alternative jet fuel was produced last year to fuel the global commercial aircraft fleet for 10 minutes — certainly not much for the average traveler to rely upon. And it’s worth noting that not all alternative jet fuels reduce greenhouse gas emissions on a lifecycle basis, as discussed here.

Chart, fossil vs alternative jet fuel use, 2013 and 2019

Fossil vs. alternative jet fuel use, 2013 and 2018

A handful of European carriers have spun up ways for consumers to offset their CO2 emissions by paying a premium for alternative fuels. But those fuels remain very expensive. SAS, for example, has a program that allows fliers to purchase alternative fuels to cover their flights at the cost of €10 per 20 minutes of flight. That rate could increase the cost of a long-haul flight by about 50%. Lufthansa is marketing alternative fuel purchases on its flights as an alternative to classic offsetting, with implied costs of about U.S. $500 per tonne. So that’s one option, albeit one that seems unlikely to scale quickly, given public demand for ultracheap flights.

Another approach that could actually save you money is to choose more fuel-efficient flights. I advise travelers to fly like a NERD, as shown in the figure below. N stands for new aircraft. E points to flying in economy class. R stands for regular. D stands for flying direct. These tricks will reduce the CO2 linked to your trip and steer airlines to adopt lower-emitting aircraft, routes, and configurations in the future.

New Newer aircraft like the A320neo or Boeing 787-8 have ~15% lower fuel burn than older designs
Economy More seats, and fewer unfilled seats, means lower fuel burn per passenger.
Regular Regional jets and very large aircraft with four engines are fuel intensive. Regular, medium-sized jets tend to be more fuel efficient.
Direct Fly direct, without layovers, where possible to reduce fuel burn due to circuitous routes.

Fly like a NERD to reduce your climate footprint

Flying on new aircraft reduces fuel burn and CO2 because, on average, each new generation of aircraft burns about 15% less fuel than the generation it replaces. Also, an existing type often gets modest (up to 5%) improvements in fuel efficiency across its production run, so a newer aircraft of the same generation may emit less CO2 than one first delivered 10 years earlier.

On a systemwide basis, flying in economy is more fuel-efficient for two reasons. First, more seats per unit of floor area amortizes the empty weight of the plane over more seats. Second, a higher proportion of economy seats tends to be filled on a typical flight compared to business-class or first-class seats. Taken together, we’ll all have more neighbors to share the emissions with when flying in cattle class, although the impact of shifting a single person from the back to the front of a given flight is basically zero.

Regular points to avoiding both very small (regional jets) and very large (quad aircraft like the B747 and A380) planes, which tend to be less fuel-efficient than regular narrow body and widebody jets. Finally, whenever possible, try flying direct to avoid the extra miles from layovers that take you away from a straight line from your origin to destination airport. Using these tricks, you can reduce CO2 emissions from your flights by 20% to 45%, depending on the route.

I should caveat all of this by saying that none of us should have to do this sleuthing ourselves. The data needed to select lower-emitting flights is already available – airlines and travel search engines just don’t show it to you. Luckily, they may have to soon. Sweden may introduce legislation next year that requires carriers to disclose information about the carbon intensity of flying compared to other modes of transport. The European Aviation Safety Agency is investigating labeling schemes for aircraft, airports, and airlines, and polling suggests that there’s wide support in the United Kingdom for airline reporting of carbon data. So it may be only a matter of time before you won’t need to fly like a NERD anymore.