by Diane Englander

The first thing you need to know about aviation’s effect on climate is that carbon emissions cause less than half the harm.

When someone concerned about climate change thinks about airplane emissions, she thinks about carbon. In fact, carbon has also been the focus of high-level efforts to regulate aviation both within various countries and internationally. In October 2016, the United Nation’s International Civil Aviation Organization and its 191 member states finally reached an agreement to cap international aviation emissions by limiting CO2 with a carbon offset approach.

But the twist is that the agreement doesn’t cover other aviation emissions, which could double or more the warming effects of CO2 alone.

Delft University atmospheric physicist Volker Grewe, who specializes in aerospace emissions, has concluded that “Aviation is different from many other sectors, since its climate impact is largely caused by non-CO2 effects, such as contrails and ozone formation.”  

Nitrogen oxides emitted in flight cause the ozone formation Grewe refers to; sulphate aerosols and water vapor emissions create contrails and cirrus clouds, which also contribute to warming. These effects result in a doubling or more of the warming effects of carbon emissions alone, according to a study commissioned in 2015 by the European Parliament’s Committee on Environment, Public Health and Food Safety (ENVI).

The International Panel on Climate Change recognized the role of these non-carbon emissions in a 1999 report. So why no action to regulate them?

First, the magnitude of these additional warming effects has proved difficult to pin down, because the emissions are short-lived, so their effects are localized and subject to the variables of location, altitude, season and time of day. With cirrus cloud formation, the science of trapping thermal radiation is still not fully understood. Carbon dioxide, on the other hand, has global effects because it persists in the atmosphere for a very long time.

Second, these same variables complicate thinking about how to reduce the warming effects. There are two obvious ways to reduce the harm from CO2 emissions: use fuel that produces less carbon — and use less of it.

For non-carbon emissions, the possible solutions are more varied and complicated. They include

• less flying at night, when the radiation that contrails and cirrus clouds reflect back to earth are not partly offset by reflecting radiation away from earth, as happens during the day
• less flying in winter, because contrails and clouds are more likely to form when it’s cold
• flying lower, because greater altitude increases the effects of nitrogen oxides
• rerouting to avoid regions particularly sensitive to non-carbon emissions, such as tropical rainforests and alpine regions, among others.

While airlines already have a strong incentive (their bottom line) to burn less fuel (“the US commercial aircraft fleet emits just one-third the CO2 per passenger-mile that it did back in 1970”), they have no profit motive to think about flying their planes at different altitudes, at different times of day, on different routes. In fact, rerouting could cause more air traffic congestion just as we’re trying to reduce congestion, and would use more fuel. Another wrinkle is the challenge of predicting the effect of the several variables at any given time.

Finally, the international nature of much air travel makes regulation by any single national government difficult, which has perhaps allowed carriers to protect all air travel from meaningful regulation.

For now, what can be done? Just one powerful action: fly less.  

Remember, carbon is at most half the story. If you’re concerned enough to carry a reusable water bottle, consider putting solar panels on your home or drive a hybrid car, keep in mind that one economy-class round-trip flight from NY to London has a warming effect of about 3 tons of carbon per person. That’s a large part of the average American’s carbon footprint of 19 tons per year.

You can calculate the impact of your intended flight here. Just remember to double the number. Then, if a video meeting will save you a business trip, do it. If a vacation closer to home is an option, take it. Stop the damage caused by flying reflexively. Planes are hurting the climate twice as much as the general public thinks. 

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Footnotes:

1. https://www.reading.ac.uk/news-and-events/releases/PR712903.aspx
2. http://www.europarl.europa.eu/RegData/etudes/STUD/2015/569964/IPOL_STU(2015)569964_EN.pdf,  p. 14.
3. https://www.sciencedaily.com/releases/2016/02/160218060945.htm
4. http://www.vox.com/2016/5/6/11569202/aviation-emissions-solar-plane

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