Txchsplainer: How Do You Calculate the Carbon Footprint of Flying?

July 18, 2011

With the summer air travel season fully underway, GE Reports presents a look at the carbon footprint of flying – assembled by the Txchnologist, the GE-sponsored online magazine about new technology:

By now, we’re all familiar with the idea that our lives, from the food we eat to the cars we drive, have carbon footprints. Flying comes under special scrutiny both because jets pump carbon directly into the upper atmosphere and because it is often volitional — we fly for business instead of teleconferencing and jet to Cabo for an all-inclusive vacation instead of going camping.

But measuring carbon emissions from airplanes is tricky and results can vary widely. The U.N.’s International Civil Aviation Organization (ICAO) set out to end disputes over aviation emissions in 2008 by introducing one carbon calculator to rule them all, complete with a section on methodology (pdf). Not that it settled anything. One prominent critic noted that the ICAO calculator doesn’t allow flyers to select the aircraft they’ll be flying on or indicate whether the flight is full or empty. “In general,” a contributing editor to Consumer Reports noted, “the more information a calculator requests about your trip, the better.”

It may not matter a whole lot if you are responsible for 804 pounds of carbon dioxide on a one-way flight from Los Angeles to Newark, as ICAO claims, or almost 1,200 pounds, as ClimateCare does, or 644 pounds, as TerraPass suggests. But if the European Union starts making airlines pay for their carbon emissions, which it has announced plans to do in 2012, passengers might start to care how their contribution is calculated. Especially if airlines start charging for it. So we decided to take a peek underneath the hood of ICAO’s methodology. Here’s what we found:

Click image to enlarge:

 

Carbon footprints of some popular domestic and international routes according to calculators from ICAO, TerraPass (which requires users to choose their airline) and ClimateCare:

New York Laguardia (LGA) – Chicago O’Hare (ORD)
ICAO: 280 pounds of CO2
TerraPass (on American Airlines): 316 pounds of CO2
ClimateCare: 308 pounds of CO2

New York Kennedy (JFK) – London Heathrow (LHR)
ICAO: 849 pounds of CO2
TerraPass (on Delta): 979 pounds of CO2
ClimateCare: 1,700 pounds of CO2

Los Angeles (LAX) – San Francisco (SFO)
ICAO: 163 pounds of CO2
TerraPass (on United): 166 pounds of CO2
ClimateCare: 154 pounds of CO2

Hong Kong (HKG) – Taipei (TPE)
ICAO: 218 pounds of CO2
TerraPass (on Cathay Pacific): 188 pounds of CO2
ClimateCare: 220 pounds of CO2

Sydney (SYD) – Los Angeles (LAX)
ICAO: 2,064 pounds of CO2
TerraPass (on Cathay Pacific): 2,100 pounds of CO2
ClimateCare: 4,034 pounds of CO2


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  • Russell Ziprik

    You have an error in your article. You state that on a flight from LAX to EWR, that you would burn 31,800 lbs of fuel (approx 4650 gal of Jet-A). You also state in the figure that 802 lbs of CO2 per person would be created. With 170 souls on board, 170 x 802 = 137,360 lbs??? How can you create more carbon than the weight of the fuel???
    I think you meant 808 lbs total for the flight.

  • Ken

    Dear Ressull,
    One mole of fuel can produce a couple of moles of CO2.
    If we take an example of Octane (similar to gasoline) as a fuel, the chemical equation is given by: C8H18 + 12.5*(O2 + 3.76N2) –> 8*CO2 + 9*H2O + 47*N2. In this case, one mole of fuel generates 8 moles of CO2. In terms of mass, 114 kg fuel (=12*8+1*18) produces 352 kg CO2 (= 8*(12+2*16)) if the fuel is ideally (i.e., stoichiometrically) burned.

  • GE Reports Editor

    This is where we get deep into weeds — and you can see the documentation if you click the PDF link in the Txchnologist story. You have to reconvert the numbers to metric, then multiply the fuel tonnage by 3.157, which is a constant representing the number of tonnes of CO2 produced by burning a tonne of aviation fuel. You also have to factor in that while the average flight has 170 seats, they are not all filled (the load factor part of the equation). ICAO does not provide enough data to reproduce the exact calculation but the equation is 3.157x(total fuelxpassenger to freight factor)/(number of economy seatsxPassenger load factor)

    So, yes, the weight of the CO2 emissions exceeds the total weight of the fuel.

  • Russell Z

    Hadn’t thought about the chemistry. I tried to quit thinking about it after college.
    You have some valid points there.

    The article states that 808 pounds of carbon is produced per passenger and there are 170 passengers.
    Based on that information simple math then tells you that 137,360 lbs of carbon are produced for this flight.
    However, per multiple sources, 1 gallon of Jet-A (i.e. Kerosene) produces approx 22.4 lbs of carbon per gallon. Therefore 4650 gallons of Jet A at 22.4 lbs per gallon comes to 104,160 lbs (not 137,360).
    How you divide that among freight and passengers, doesn’t really matter, but lets have some fun.
    Empty weight of a 757 is 127,520 lbs
    Max fuel load is 11,489 gallons (or 78,125 lbs)
    Max take off weight is 255,000 lbs.
    So if we add fuel weight to the empty weight we get 202,645 lbs. Subtract that from the MTOW of 255,000 and we have 49,355 lbs left for passengers and cargo.
    Per the FAA the standard person weights 170 lbs. So 170 passengers weigh in at 28,900 lbs.
    Subtract that from the 49,355 leaves us 20,455 lbs for freight.
    So the split between passengers and cargo is 59% for passengers and 41% for freight.
    Back to our original flight info we know we produced 104,160 lbs of carbon. That means the passengers are responsible for 59% of the carbon produced, which comes to 61,454 lbs. Divided evenly among our 170 passengers and we get 361.5 lbs per person.

  • GE Reports Editor

    I love that you’re thinking about this so deeply Russell.

    But you’re still assuming that there are 170 passengers on this flight. That is actually the number of seats. Multiply this number by the load factor for this route – which I don’t know and ICAO doesn’t provide. The average for all domestic flights, per the U.S. Bureau of Transportation Statistics, is about 80 percent.

    That gives us 136 passengers * 804 lbs = 109,344 lbs of CO2, which is close to your 104,160 number.

    It seems you’re also assuming that baggage is freight. For the purposes of this calculator it is considered passenger weight – an assumed average of 100 kg, or 220 pounds. The calculator also assumes a further 50 kg of infrastructure to account for onboard equipment for passenger use. I don’t know what the passenger to freight factor is for this flight, but I’m assuming it’s close to 1.

    In any case, this piece is about how one organization, the International Civil Aviation Organization, calculates the carbon footprint of flying. If we take their equation (in metric) it looks like this

    Carbon footprint per passenger =3.157*(Fuel burn of 14,412 kg* passenger to freight ratio) / (170 seats *0.80 load factor). Assuming that the passenger to freight factor is 1 that comes to 334 kg per person or 736 pounds per person. That’s still short of the mark, so I’m assuming that the load factor is even lower – perhaps 70-75 percent

    It’s fair to dispute their conclusions, but as far as flight carbon calculators go, their numbers are on the low side.