Flight Emissions Are a Big, Hairy Problem
If you traveled in 2019, then you were aboard one of 40 million flights that had departed worldwide—more than 100,000 trips per day (ICAO). That number could explode in the coming years.
The effects of CO2 emissions from air travel create quite a conundrum for would-be environmentalists. This became apparent when I set out to trace my transportation and residential energy carbon footprint over the last 12 years.
While I had developed spreadsheets for accurately estimating per passenger transit emissions, along with meticulous record-keeping of my vehicle trips and home energy use, I was thunderstruck by the extent to which flight emissions consumed my overall carbon budget.
A personal assessment
From 2008–2019, I had averaged 3.5 economy class round-trip flights, domestic and international, for work and leisure. Here’s how CO2 emissions from air travel compared to CO2 emissions from everything else:
First, here are three important caveats you need to know:
- Flight emissions matter if you fly. Many Americans don’t fly at all. Just 12% of Americans take two-thirds of all passenger flights (ICCT, 2018). Even if you don’t fly, flight emissions may matter insofar as your purchasing decisions rely on air freight shipment, which is considerably worse than transporting the same volume of cargo by sea or land.
- These figures include only the CO2 generated by burning fuel—not any of the externalized emissions associated with planes, airports, and ground operations. There can even be wide variation between per passenger emissions for different airlines. The same goes for everything else: vehicle emissions don’t include emissions from highway construction or battery production, nor do natural gas emissions include emissions from fracking operations or pipeline construction.
- Everyone’s transportation mix is different. So is your fuel mix. For instance, I don’t drive all that much, and I prefer to ride my bike to work. If you have a substantial work commute, and you drive a gas-powered car, your vehicle emissions will be higher than mine and may therefore be a bigger source of emissions than flying.
Needless to say, airplane rides are one of my environmental failures.
But it gets worse, because aviation emissions are generally released into the upper atmosphere, where its impact is amplified. At the interface of the troposphere and stratosphere, higher-intensity light produces more ozone (O3) from nitrogen oxide emissions (NOx), which has a greater warming effect than the same emissions released at sea level.
Long-haul flights take place at higher altitudes and release more oxides of nitrogen into the upper troposphere. In my simplified accounting of flight emissions, I’ve taken into account the difference between short and long-haul flights, but only for CO2. That means other, non-CO2 induced effects are unaccounted for.
Does this mean short-haul flights are better? No.
Many of my domestic flight trajectories involved layovers, which require more climbs and descents during the course of the trip. The phase before reaching cruising altitude consumes more fuel—upwards of 25 percent of the fuel used during a flight (Worldwatch, 2019). Even when accounting for the secondary effects of high-altitude non-CO2 emissions on long-haul flights, domestic and other short-haul flights are the most environmentally damaging form of travel.
Aviation emissions will soar
Here’s the scoop on global and U.S. aircraft emissions:
- Commercial aviation accounts for 2.5% of the world’s global energy-related carbon emissions (IEA, 2018). Include non-CO2 effects and the industry’s total contribution becomes 5% (EESI, 2019).
- Flights from airports in the United States were responsible for almost one-quarter of global passenger CO2 emissions (ICCT, 2019). The top five commercial aviation emitters? The U.S., China, U.K., Japan, and Germany.
- Aircraft contribute 12% of U.S. transportation emissions (EPA, 2018). But road vehicles are still the biggest source of U.S. transportation emissions. Medium and heavy-duty trucks are twice this amount, 23%. Light-duty passenger vehicles contribute the most, a whopping 59%.
Innocuous, right? Commercial aviation in the U.S. contributes a paltry 12%. Not so fast. There are two important reasons why this reasoning may prove to be perilously wrong in the near future.
First, we are traveling farther and more frequently. Passenger flights are up more than 300% since 1990 (IATA, 2019). This number could triple in the next three decades, given the projected growth of passenger air travel and freight (ICAO, 2018). And in economies with a burgeoning middle class, like China and India, that number may rise even faster.
Second, unlike cars, aircraft cannot be entirely battery powered—yet. At best, airline manufacturers can make small efficiency gains with modifications to airplane bodies and engines, and airlines can include fractional amounts of sustainably sourced biofuels in their fuel mix. Hybrid electric engines may provide a bridge to fully electric aircraft fleets, but a full-scale electrified future is decades away.
Herein lies the unremitting environmental dilemma with commercial aviation: It’s growing like gangbusters while there are few “drop-in” fuel alternatives and no revolutionary battery electric aircraft.
Contrast the upgradability of airplanes with light, medium, and even heavy-duty vehicles, all of which can be swapped with electric engines. And their batteries can be recharged from renewable energy sources. Of course, this transformation of the vehicle sector is only just getting started. But commercial aircraft don’t even have a theoretical alternative; the batteries weigh too damn much.
So, as other sectors of the global economy become greener—with more wind and solar power, for example—aviation’s proportion of total emissions is set to rise.
You can observe the same shifting proportions in my transportation and residential energy carbon footprint: Choosing 100% wind and solar sources for my electricity effectively brought electricity emissions to zero. Switching from a gas-powered vehicle to an all-electric vehicle had the same effect. Same, too, for trading in my gas-powered scooter for an electric bicycle.
The airplane does not yet have a low-carbon alternative.
What can we do about it now?
Aside from holding out for a possible Tesla narrow-body jet or a Boeing wide-body jumbo jet that runs only on electrons, there are a few strategies to consider that might reduce your environmental burden:
- Opt for taking fewer connecting flights to your destination. It may cost more to take a direct flight, but now you have a great excuse.
- Consider taking an extended trip over a longer period of time, rather than taking two shorter trips at different times. This strategy works for visiting megaregions in the U.S. or neighboring countries abroad.
- Choose airlines with overall newer aircraft fleets, or routes that tend to use newer, more efficient aircraft. (Delta has one of the oldest fleets in the U.S., with an average fleet age of 14.5 years as of 2020.)
- Don’t fly first-class, which takes up more space with fewer people.
- Pack light. Increased fuel consumption is one reason why airline operators charge additional fees to transport heavy luggage. The total weight of the aircraft directly affects its emissions output.
- Buy carbon offsets to reduce your carbon footprint. This option may become increasingly overextended, however, as countries preserve land to offset their own rising emissions.
- Choose rail or a coach bus for short domestic “hops” and inter-city travel (or inter-country travel in Europe). It’s also more affordable.
- For non-essential work trips, advocate for teleconferencing instead. Collaborate with your boss, peers, and customers to promote a culture that recognizes the value of remote meetings.
- For essential work trips to destinations that interest you, combine them with a vacation befitting of a cross-country trek through the sky. Use that free round-trip flight to stick it to the Man!
If you’re up for it, ditch human flight altogether and sail to your destination like climate campaigner Greta Thunberg, who chose to sail to a UN climate conference in New York in a zero-emissions yacht rather than fly.
Clearly, Greta outshines me in every way.
EESI: Environmental and Energy Study Institute
EPA: United States Environmental Protection Agency
IATA: International Air Transport Association
ICAO: International Civil Aviation Organization
ICCT: International Council on Clean Transportation
IEA: International Energy Agency
IPCC: Intergovernmental Panel on Climate Change