okay, so clear this bit for me, please.

if "one person or four drives in the generic mid-size car, it emits about 104 kg CO2 total."
how does that compare with one person or 4 or 40 or 140 flying in the plane? surely the weight of that 1 or 4 should make no difference to emissions. 40, maybe. 100, probably.

any info on that ready at your fingertips would be most appreciated.

thanks

Ah, but my husband is a mathematician, so all that math will make him happy.  Thanks for answering one of our random questions!

Natalie W. in North East

But!!!

there's always a but...

if the plane is flying anyway, a commercial flight on a regular schedule with an empty seat, then isn't it less carbon to hop on and not drive?

Hi, dave9778
While I certainly see what you're saying, this is basically a twist on the argument, "Well, the product has already been made and is in the store - I can't help the production impact, so I may as well buy it!"
If fewer people fly a given route, choosing instead to take alternate transport X, then the regularly scheduled commercial flight will stop being run, or will run less often.

Slightly ahead?  The cars come out almost half the CO2!

The answer is of course to take the train.

I'm with mohoshe, how come 1-4 people in a car makes no difference in carbon emissions, but each additional person in a plane raises the carbon footprint for the flight? I know my car uses more gas when I drive from Portland to Seattle with 4 people in it, albeit far less than 4 cars with one person would, and I am sure a full plane would require more fuel than an empty one, but it seems like the change between one additional plane passenger would be a negligible increase in the overall weight of the flight. Also, it seems like this is also a question of infrastructure as well, if everyone suddenly quit flying from any city within a 300 mile radius of Boston, the resulting traffic jams would considerably increase the caron footprint of the drive. So a few of us can feel better about our own carbon footprints but it doesn't seem to be a real solution. It would seem that the train is by far the best option overall.

I disapprove of the way this article, and many others, are written. Two things specifically annoy me, first is the confusion about the primitive unit of co2 production, and the second concerns using unrigorous, untransparent physics, with difficult to interpret numerical terms.

Concerning my first issue, consider the following:

"I can further tell you that the Boeing 737-300 that United flies on
its Philadelphia-Boston route holds around 128 passengers, so if the
plane were full (wedding crashers!), the total emissions would be a
bit higher."

Obviously the plane will emit only slightly more CO2 with another 28 people onboard - in fact it will emit far less CO2 per person. Why does the author take the per person carbon as the primitive, when obviously you can only get per person carbon by dividing out of a single total carbon emission - that of the entire plane. It is in no way true that the plane produces X kg of carbon because each person contributes their little amount. Rather, the plane produces X and because we like to calculate everything, we attribute X/N where N is the number of paying passengers on the plane KG to each passenger.

Concerning my second worry, what is 0.3442 kgCO2/mile? Certainly a number from some website somewhere, but how do I know it in any way connects with reality? I suppose if its about 2.3 kg from 1 liter,
that means they are calculating for 6.7 miles to the liter, which is
25 miles to the gallon. There are not very many "mid sized cars" built
today which get 25mpg on the highway. I'll give you five dollars if you can find one rated so poorly on fuel economy.gov which qualifies as "mid size". I turned that figure exactly on
the trip to portland, which was not all highway, and which had 6
people and luggage in a 20 year old, full size car.

Aside from these two issues, the conclusion is bonkers: "Per person, this journey
isn't dramatically different from a carbon angle, with the 100 cars
coming out slightly ahead."

Slightly ahead? 10 000kg versus 18 000kg? How is that slightly ahead?
Also, the cars were all packed with organic footons, try to get those
on  the plane!

Another thing, it's not the same to release co2 at ground level versus tens of
thousands of feet in the air. Also, for your not flying to make a
difference, you have to fly enough less that flights get canceled, and
that means people lose jobs (which for some reason upsets people). Also, planes put a lot of water in the air, which forms clouds, and might be responsible for global cooling.

It is, however, absurd to do these calculations at all - it relies on individual desire to save the world to, save the world. People cannot, and should not, be expected to do this. Put a price on carbon, and then people will be green by just trying to save money.

You should also calculate in the driveing you have to do when flying. Kind of hard to get an average but the extra transportation needed when flying can be considerable.