There are many figures regarding how much CO2 is emitted per passenger and per km.

However, I have not been able to find anywhere how much CO2 would an airplane emit if it has to carry an additional kg of weight.

I think it would be a very interesting figure.

Does anybody have an idea about how to find this out?

  • I would think it would correlate with fuel consumption, at least to some extent, so I would start there; airlines track their fuel usage quite exactingly. – choster Jan 21 at 20:15
  • I seem to recall reading that a ballpark figure is 1 kg extra CO₂ per 1 kg extra weight for a transatlantic flight, but I don't have a source right now. – gerrit Jan 22 at 8:38
  • It is indeed an interesting question, but when thinking about your own behaviour remember that your getting on a plane is also contributing to the airline's bottom line and enabling it to keep flying, helping to keep flying socially acceptable, signalling to policy makers that there is a demand for flying, etc. So there is a good case for acting based on the CO2 per passenger km, rather than the marginal CO2. Assuming you are interested in sustainability. – aucuparia Jan 22 at 16:17

A few years ago, a question popped up that spurred me to do some research and crunch some numbers (https://sustainability.stackexchange.com/a/6204/4886):

I just calculated some more specific numbers for the opportunity cost of a single passenger on an A 300-600 over a 2,000km trip. Assuming the plane is half-full of just about everything (fuel, cargo, passengers, etc.) it works out to be ~26L of aviation fuel. That's it. You getting on the flight will only add 26L to the amount of fuel consumed by the plane over the entire trip. That's about 69kg worth of CO₂ emissions — a far cry from the 1.3 tonnes you are worried about. How far can you drive with 26L of petrol in your car?

The numbers vary, of course, according to the type of plane, the distance flown, the direction and speed of the wind, temperature, humidity, and a whole host of other factors. If you wave away the ones beyond your control, play the averages game, and reduce it down to a simple CO₂/passenger figure, the answer I got was 69kg.

I can't remember what the airline's average gross passenger weight (passenger, carry-on and luggage) was, but wouldn't be surprised if it was around the 95kg mark. So each kilogram of mass being transported on a 2,000km international flight by one of those Airbuses works out to about (69/95=) 726 grams of CO₂.

Over a 2,000km trip, therefore, the emissions would be about (726/2000=) 0.36 grams of CO₂ per kilometer flown per kilogram of mass transported.

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  • Long haul trips are the best case, right? It would be cool to see this compared to shorter trips - eg New York to DC or even Boston to New York. – Jean-Paul Calderone Jan 22 at 13:18
  • @Jean-PaulCalderone Generally, yes, long-haul is where flying really does make sense. Once the distance drops below ~1,600km air travel is no longer the clear winner, and it gets worse as the distance shortens. Flights shorter than ~400km should probably be banned outright. Electric planes will change all that, but we're stuck with dinosaur juice-powered planes for the time being. – Tim Jan 23 at 7:51
  • Awesome answer, thanks! So it does indeed make a real instant difference if one does board into an airplane or not. This could help to counter-argue when somebody says: "the plane is going to flight anyway, so it does not matter whether I fly in it or not". – J0ANMM Feb 6 at 19:11
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    @J0ANMM Well, technically, if you consider 0.36g/km/kg to be 'a real instant difference', then yes, it does. But since 99.936% of the emissions will still be released even if a single person refuses to board a long distance/international flight, those that say is doesn't make a difference are 99.936% correct. The math favours avoiding short (<1600km) domestic flights (which do have a possibility of being consolidated or cancelled) and boycotting flights <400km entirely. There's nothing really wrong with flying long distances, or to international destinations, on under-capacity flights. – Tim Feb 7 at 10:33
  • Specifically, if you need to travel >2000km and/or to another country, then boarding a plane that's less than about ⅔ full is an environmentally acceptable (perhaps even 'responsible') thing to do. – Tim Feb 7 at 10:38

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