In Which I Go Home for the Holidays (Soon!)
by Sarah Gillig Sunu -- November 30th, 2012

Final papers, presentations, and projects are keeping me very busy!   However, I’m really looking forward to going to my hometown, Frankfort, Ky., for the family Christmas celebrations.

Usually  there isn’t a lot of debate about how we’re getting there.  For the last 10 years I’ve been living more than 800 miles away, and most of that time I didn’t have a car or a driver’s license (I didn’t really need them until I got married).  I was flying; end of story.

But this year, there’s a choice.  My parent’s house is only about 350 miles away (8.5 hours in the car, blech), and we live about 20 minutes from a major airport.  For the first time in ages, there are viable options!

Steve and I have already decided to drive because of the dollar cost of flying this time of year, but I got curious about the carbon cost of driving versus flying.  Is there a big difference?

There are a number of online calculators available to say how much money the gas I buy will cost, how many miles it is, and how long it will take, but most of those didn’t tell me how much carbon I’d be emitting.  Eventually I found a few that would tell me the carbon cost of my travel options—but I still had some questions.

These results are from the Native Energy carbon calculator.  Round trip drive from Chapel Hill to Frankfort: 1 ton of CO2.  Round trip flight from Chapel Hill to Frankfort: 1 ton of CO2.  Wait a minute….

Estimate from the Native Energy calculator of the carbon cost of flying home.

Common sense dictates that it takes a lot more energy for my body to fly through the air than roll along the ground, due to the force of gravity, etc.  This result doesn’t tally with that (particularly since our little Yaris is fairly fuel-efficient for a non-hybrid), so what gives?  I went to “How we calculated this” to find out.

Their equation for the carbon consumed by flying is:  Flight Miles Traveled x Flight Emissions Factor (fuel use and length of the flight) x Radiative Forcing Index (based on Intergovernmental Panel on Climate Change data on the overall impact of CO2 in the air)=Total Tons of CO2 Produced.

The equation for carbon consumed by driving is:  Miles Traveled/ Miles per Gallon x CO2 Produced per Gallon= Total Tons of CO2 Produced.

Estimate from Native Energy of the carbon cost of driving home.

Hmm.  The equation for flying doesn’t say anything about whether that’s the CO2 for the whole plane, no matter how many people are on it, and the equation for driving doesn’t say anything about the number of passengers either (relevant, since my husband is of course coming with me).  I decided to check the results on another carbon calculator.

Most carbon calculators want to give you a total estimate for all your carbon consumption, but some will give you step-by-step estimates.  I decided to try this one from Carbon Footprint for comparison.

Estimate from Carbon Footprint of the carbon cost of flying home

Here it says my carbon footprint for two round trip flights from Raleigh to Louisville is 0.5 metric tons of CO2, and the carbon footprint for one 700-mile (Chapel Hill to Frankfort and back) trip in our car will emit 0.20 metric tons of CO2 (they also had my car’s model information in a database so they used that instead of my estimate).  Unfortunately I couldn’t find how they make their calculations on this website, but based on my comparison of the results, it looks like this one breaks down carbon emissions on a flight to a per-passenger basis, which is what I wanted to know (though not all flights are always full).

Even with the decrease to a per-passenger CO2 footprint for the flight, it’s still a lot less carbon for us to drive (especially when you consider that neither calculator considered how many people were in the car—with two people it essentially halves the emission rate from 1 ton to 0.5 tons (first calculator) or from 0.2 tons to 0.1 tons (second calculator)).

I’d still like to know more about the assumptions behind these calculators (do I drive the speed limit? Is my plane a 747? How much difference does the body weight of an additional person make in a compact car? Is my time valuable?), but I have to write a paper (so yes, my time is valuable!).

This exercise was mostly to satisfy my own curiosity, but both calculators that I used had one important additional step—I could choose to offset my emissions with just a click and a credit card.  I wonder if that’s a factor in their emissions calculations….

Tides for Friday, November 30th, 2012, Beaufort, NC

Low: 2:09 AM, 0.16 ft.

High: 8:41 AM, 3.56 ft.

Low: 3:03 PM, 0.34 ft.

High: 8:57 PM, 2.82 ft.

From NOAA Tide Predictions


  1. Jane Dietterich
    Dec 1, 2012

    Very interesting, Sarah! Confusing, but interesting.
    Good for you to even think about this and compare.

  2. Sarah Gillig Sunu
    Dec 4, 2012

    Thanks! It’s confusing for me too, even though it’s the kind of thing I think about a lot. See you soon!

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