How bad is air travel for the climate, really?
July 24, 2013 3:43 PM   Subscribe

I'd like to better understand the climate impact of flying, as someone who flies quite a lot but in a rather unusual manner.

So this answer makes it seem like flying is actually more fuel-efficient than driving, but is this all there is to it? Are jet fuel emission better or worse than auto emissions? Is flying bad for the environment because of the distances traveled?

Snowflake details in case anyone can give me more specific info: I have a relative who is a pilot so I can fly for free on standby. That means I am not giving the airline any economic incentive over, say, trains, which in theory I favor. I only get a seat if there is space, the plane flies either way. So in thinking about my own flying, I am really interested in marginal fuel usage rather than average fuel usage.

For people who are not in my unique situation, what is the best policy for travel? Avoid it? Take a train or bus?
posted by mai to Travel & Transportation (8 answers total) 5 users marked this as a favorite
Nature revisits some research from 2002: Can aircraft trails affect climate?

Wikipedia: Environmental impact of aviation
posted by Blazecock Pileon at 3:52 PM on July 24, 2013

Here is a study from 2013.

Regarding the airplane vs. car question, they say: "While sharing a long car journey with two or three others in a small car could reduce the emissions per person to the equivalent of a train or coach ride, making the same trip alone in a large car could have just as negative an impact in terms of emissions as taking a flight."

They conclude: "If you can, choose public transport like a train or coach for your holiday or business trip."
"Try to use flying only as a very last resort – what is emitted thereby in one trip is hard to compensate for by other personal measures like cycling, a vegetarian diet or using green electricity."

posted by travelwithcats at 4:02 PM on July 24, 2013

One thing to note is that airplanes are *very* weight-sensitive. Your extra weight on board the plane does cause it to burn measurably more fuel.

The number I heard once is that an object on board an airplane will cause its own weight in fuel to be burned roughly every 20,000 miles. So, if you and your luggage weigh 200 pounds, you'll burn one extra pound of fuel every hundred miles - about one gallon every 700 miles.

So, figure that at the margin, you'll burn less fuel by flying standby than you would driving.

Note that an airplane's actual fuel consumption is about one gallon per 100 passenger-miles.
posted by Hatashran at 6:08 PM on July 24, 2013

Is flying bad for the environment because of the distances traveled?

This is a big part of it, but related to that I think that comparing it with car is misleading because realistically, flights do not swap out car travel, flights are taken in addition to car travel.
In other words, if flying was not an option and you had to take a car or boat, I'd think more than 90% of those trips just wouldn't happen at all. People aren't going to waste two weeks stuck a car all day just getting to Boston and back for a business meeting, or spend a month crammed together cattle-class on a ship each year to visit Grandma over the sea. We'd do things other than making frequent visits in person. Car travel wouldn't increase much.
posted by anonymisc at 7:03 PM on July 24, 2013

Fly all you want, and use part of the money you save to contribute to tree-planting, basic research or political lobbying to balance out the carbon emissions of your flight.
posted by sninctown at 7:53 PM on July 24, 2013 [3 favorites]

Best answer: It sounds like the question is: how much extra fuel do you burn by taking that standby seat versus letting it stay empty and taking a bus or train instead?*

This article has a table estimating the amount of fuel consumption attributable to the weight of a single passenger for two example flights. For both flights, the weight of fuel consumed is directly proportional to the passenger's weight. The shorter flight (LHR-DUB) shows fuel consumption for an Airbus A319-100, which is a midsize plane seating about 130-140 passengers, similar to a Boeing 737, and a representative aircraft for mid-range domestic trips. The LHR-DUB flight gives a fuel consumption of 0.23 kg of fuel per kg of body weight for a 280-mile trip. With a typical jet fuel density of 6.84 lb/gal, this converts to about 0.00082 kg fuel per kg body weight per mile (0.00082 lb fuel per lb body weight per mile), or 0.12 gallons of fuel per lb of body weight per 1,000 miles traveled. So, a 160-pound person taking an otherwise empty seat on a 1,000-mile flight would consume an extra 19.2 gallons of fuel compared to that seat being empty.

That's a little bit better fuel economy than some other estimates for air travel, which typically don't vary based on passenger weight. Here's a DOE estimate showing 44.56 passenger-miles per gallon (about 22.4 gallons of fuel for that 1,000-mile flight), and this study done for the American Bus Association estimates about 42.3 passenger-miles per gallon (or about 23.6 gallons for that same flight). That bus study also estimates about 15.2 gallons of fuel to take the same 1,000-mile trip on Amtrak, or 5.4 gallons to take that trip on a Greyhound bus-- remember, study was done for a bus association. So, the extra fuel you burn by taking that standby seat could be anywhere from 4 to 18 gallons for a 1,000-mile trip, depending on how you estimate fuel use, and your alternate mode of transit (and assuming you wouldn't otherwise just stay at home). It's all better than driving alone, which would take about 36 gallons of fuel for that trip.

Put into perspective, U.S. per capita consumption of all petroleum products was about 952 gallons per person per year in 2010, based on daily consumption from here and U.S. population from here. A single one-way airline trip of 1,000 miles is very roughly about 2 percent of the average American's petroleum consumption for a year. (Five round-trips like that in a year would be an extra 20 percent, which starts to seem like a significant amount of fuel use.)

*Or at least, a question that can be answered. The impact of your personal air travel on the climate is super hard to estimate, partly because it's like asking which straw is going to break the camel's back (your share of a plane trip adds a few hundred more pounds of CO2 to the atmosphere, out of trillions of pounds the whole world is adding every year), partly because how much "bad" will happen isn't known yet since it depends enormously on our future behavior as well as decades and centuries of watching the consequences play out, and partly because "bad" can mean a hundred different unpleasant things. Maybe it would mean something if we could say every plane trip meant 10 extra gallons of Greenland glacier melt per year, and one extra Ponderosa pine destroyed by fire or pine beetles per decade, and 0.001 extra micrometers of sea level rise per century. But I do think we can say it's mostly the CO2 we care about for climate change, rather than anything else in the exhaust. While jet exhaust is dirtier than automobile exhaust per gallon of fuel burned, the amounts of those pollutants, and their potential climate effects, are very small compared to the amount of CO2 released, despite the fact that contrails and high-altitude soot can even cause atmospheric cooling by reflecting sunlight into space.
posted by Dixon Ticonderoga at 8:34 PM on July 24, 2013

Are jet fuel emission better or worse than auto emissions?

Jet fuel emissions are worse. The greenhouse gas inventory calculators I've used include a radiative forcing index of 2.8 as a multiplier on air travel CO2 emissions. This helps account for the additional, non-CO2 warming effects of air travel. More details from the Intergovernmental Panel on Climate Change and Carbon Planet (PDF, p. 7).
posted by JackBurden at 8:38 PM on July 24, 2013 [3 favorites]

A comparison between air and car travel is not as useful, imho. Almost all of the flights I make cannot be replaced by car travel without significant additional costs (both time and money), and I'd be surprised if that wasn't the case for most flight travelers. So instead, let's look at what you can do to minimize your flight travel's environmental impact!

There are carbon offset calculators and services you can use to make your flight travel a zero-carbon-footprint experience with very little effort, and for less money than the average fuel tax on a flight (not to mention far less than the average airport tax).

I fly Air Canada a lot, and they have their own official carbon offset program that allows you to donate your footprint money to good causes that help restore some balance in nature.

For a generic service that does the same, I've used Carbon Neutral Company's flight calculator.

Also, remember when that volcano in Iceland erupted, and people were talking about how a single volcano eruption causes more environmental Co2 than hundreds of flights? That eruption's resulting ash in the sky cancelled so many flights that it wound up being better in the end. The point is, it's all relative, what matters is your own personal carbon footprint at the end of the day. Or, year.
posted by KuraFire at 11:35 PM on July 24, 2013 [1 favorite]

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