Wednesday, April 9, 2008

On Calculating Carbon Emissions

I hate to belabor this point, but I'm starting to wonder if we're all approaching carbon emissions for transportation the wrong way.

Yesterday, Will from Green Couple wrote a post entitled, "What's the Best Way to Get From Here to There." He had recently driven with some friends to Wisconsin, and he calculated the carbon emissions that the trip generated. Then he calculated what his emissions would have been had he taken a bus, train, or plane. The plane was the most emissions-heavy, followed by the train, the bus, and then the car. So, Will made the most emissions-efficient choice, correct? And we should all try and carpool when we are traveling long distances, right?

Except, hold on a second. As Will points out, "A plane, train, or bus isn’t going to produce that much less CO2 just because we’re not riding."

And therein lies the logical fallacy. It's all very well to try to calculate individual carbon emissions, but the truth is, carbon emissions don't really work like we're pretending they work.

In fact, had Will taken a train, or a bus, or even (quel horreur!) a plane, the total world carbon emissions would have decreased by the amount of carbon emissions caused by the car, and increased by the amount of carbon emissions caused by Will and his friend's weight. In other words, driving a car is only the most carbon efficient method IF the carbon emissions Will and his friends's weight cause on a plane, bus, or train is GREATER than the TOTAL emissions of the car. Which seems pretty unlikely.

To put it differently, let's consider this: because Will chose not to take the bus, the per passenger miles per gallon on the bus went down. So Will might think, oh hey, my individual carbon emissions were lower because I was in the car, but actually he caused the carbon emissions of every passenger on the bus to go up because he chose to ride in a car instead of a bus.

So what's the answer here? I hesitate to draw this out to airplanes and long distance trains, but in terms of city-wide public transport, the answer is pretty clear to me. In my opinion, a city's public transit belongs to every single citizen of the city, and NOT just the citizens who use it. So the true calculation of carbon emissions would be where we calculated the total carbon emissions caused by a city's public transport, and divided it up by every citizen in that city. Then an individual calculating her emissions would add that to her individual car emissions to get her actual total.

But that's not fair! I don't ride the bus!

True. But we pay for a lot of things we don't use. To me, the best analogy here is that even if you choose to send your child to a private school, you still have to pay for public schools. Similarly, even if you still drive to work, you should have to pay for the carbon emissions of public transit. That's the point of a "public" system. We may not all use it, but its there for everyone's benefit.

Ok, Arduous, but does this nerdy mathery really matter?

I think it does. Look, a lot of us are in uncharted waters. We are faced with decisions like "organic in plastic" or "conventional in glass" every day. And a lot of the time, we rely on things like what I'd call conventional green wisdom or carbon calculators to figure out what makes the most sense. But sometimes, conventional wisdom, even conventional green wisdom, is wrong. And that can lead us to make decisions that might not make the most sense. For example, if a bus I was taking only had three people in it, I might think, oh well then I might as well drive because that is the most carbon efficient. Or I might think it made more sense to drive across country to see my sister than to fly. But the reality is, those buses and planes ARE going to be in service no matter what I do. So, to me, the logical choice is to always err on the side of a communal form of transportation, be it a bus, a train, or yes, even a plane. Because while I believe that it is possible to eventually cause a decrease in bus paths or plane rides, we also have to deal with the here and now. Besides which, you have to ask yourself, do we really want all those people on buses, trains, and planes in cars and on the roads instead? Is that really the answer?

(By the way, Will, I hope you understand I just used you as a guinea pig. I thought your post was great, and incredibly thought provoking which is why I ended up writing this post in response. And, needless to say, I am certainly not casting aspersions on your choice to take a car to Wisconsin. I like road trips myself. And I'm currently hating on the bus. But that's another story for another day.)


Unknown said...

The only thing I wonder about the plane logic is that without filling certain amount of plane capacity, airlines would probably cancel a flight or combine flights, at least in the long run since it is no longer profitable to fly half empty planes.

So I think if some of us reduce our flying, there will be fewer planes in the sky. I am not saying that cars are more efficient though. I suspect the current CO2 calculation does not include the resources spent on infrastructure maintenance. It's all pretty murky. My interest will be which mode of transportation will improve its fuel efficiency first.

Unknown said...

I do agree with cindy that the logic in your post only works up to the capacity of the current planes, buses in service. You can't really divide those emissions by everyone in the city because I doubt that the LA metro for example could accommodate the entire population of LA everyday.

I think in a way by not using buses or planes we are sending a message that only becomes significant when enough people don't ride that they run one fewer flight, etc.

I was really pleased though to see somebody, ANYBODY challenging the whack logic which is carbon calculators. Those things make me crazy. They are about as accurate as shaking your butt and calling it the tango.

PS I thought your post was excellent as was Will's :-)

ruchi said...

Just to be clear, I am not saying that flying in planes is awesome. I'm just saying that I think its the better choice than driving. Obviously, taking the bus or train would be even better.

Yes, eventually airlines might cancel or combine flights. But I guess the question is, what are we trying to accomplish? Are we trying to accomplish potential carbon reduction later or actual carbon reduction now? For me personally, I think actual carbon reduction now makes the most sense for me. Everyone is different, and has differing opinions and goals, but for what it's worth, here's my rationale:

I think the environmentalist ideal of getting people to stop flying FOR ENVIRONMENTAL REASONS is a pipe dream. Airline travel has actually been regularly increasing, not decreasing. Combine that with the fact that I only know two environmentalists who have forsworn flying, and I think we have a problem. Again, this is just my opinion, but there it is.

I think that reduced airline travel MAY well happen, but if it does, it will be because airline travel becomes more expensive, not because people are choosing not to fly for environmental reasons. If that's the case, then reduced flying will happen on its own and my symbolic decision to drive instead of fly won't have impacted airline travel, PLUS I will have increased carbon emissions by driving.

But I just want to reiterate, I am strictly speaking in terms of deciding whether to drive or to fly. Obviously, the "best" answer from a carbon-emissions standpoint is to just not travel. The second best answer is to travel by train or bus. So really, I'm talking here about choosing between the lesser of two evils. (Though I know, that for myself, I do often have to make that "evil" choice.)

ruchi said...

SDG, you're right that the LA metro couldn't accomodate the entire population of LA every day. But, that wasn't really my point in having everyone equally share the carbon emissions of public transit. I meant it more in terms of the fact that I believe public systems should be paid (whether in money or carbon) by everyone, and not just by those who use them.

Yes, the LA metro could not accomodate the entire population of LA. Similarly, the fire dept could not put out a fire if all of LA caught on fire. And if every single private school in Los Angeles closed, the public school system could not accomodate every single student.

But that doesn't negate that they are public systems in everyone's best interest, and that they should be, in my opinion, treated as such.

Grad Green said...

I think this is a great post. I have been thinking about this calculation a lot lately -- is it better for me to drive cross-country to visit my family (probably 4500 miles total round trip) or to fly? It would be about equal in cost, after renting a car at my destination, so that's not really the deciding factor. I don't think I could survive a trip that long with 3 little kids in the backseat, so realistically flying is the only way for now. (Oh! I feel so guilty!)

But it's true that if enough people fly, they will add more flights. So, I have a solution! Wait until the last minute and fly standby (assuming of course that you have the money to fly at the last minute, which I don't). But if you fly standby, you know there are empty seats in a flight that is already taken off.. Then your C02 emissions are only from your extra weight.

Unknown said...

arduous, you hit the nail on the head "I think the environmentalist ideal of getting people to stop flying FOR ENVIRONMENTAL REASONS is a pipe dream." That's the reality. You know my thoughts on not traveling (and flying) - not gonna happen. Reduce maybe, but not eliminate.

I was just posing a theoretical calculation. I guess it sort of illustrates the frustration people have about carbon calculators.

To me, taking train and buses are no brainers (compared with cars), because they consumer a lot less energy thus emit less GHG. Flights are often brought up separately because the intensive fuel consumption.

But what if we can paste solar thin films on the surface of the airplane and partly use solar energy when flying? Science fiction? Maybe for now. But it'd be cool though...

hgg said...

Very good post and the dilemma hits me every time I have to travel for work or to see family. Driving is out of the question, takes too long time and too expensive (yeah, we don't have as cheap fuel as you do). If I were to go by train I would probably spend 24 hours and change trains 5-7 times. And I wouldn't be able to afford it because train tickets are so expensive. Did you know that the train ticket between Paris and London is about twice as high as the cheapest flights you can get? It sucks. The cheapest flight from Paris to the Goose would be about 70 euros. By train that would maybe take me to Brussels.

Sam said...

Although I calculate my rioting numbers faithfully every month, I must admit that I'm not sure what the numbers really mean. I am not that brilliant, so the entire issue with reducing carbon emissions don't really make any sense to me. I'm guessing its a good thing because so many say its so. But how do I know that? This must sound really silly.

I look at my actions on a very practical level: I ride a bus because my transit pass is 100% free. I ride a bike and walk because its expensive to own an auto and its not practical to own a car and deal with the related problems in an urban environment. I'm reducing plastic because plastic bags hanging on trees is an eyesore and I don't like to see a seagull's guts full of plastic bottle caps.

I don't know how to articulate all my feelings, but the Skeptical Environmentalist (a book I read) did bring up some good points. Much of the larger picture and real point of these calculations isn't really brought forth because of its complexity. But I'd like to see it anyway.

Sam said...


Q for arduous: Do you have any favorite neighborhoods in LA? I've been "exploring" the city via google maps' Street View feature. I wandered around Compton a few days back and it didn't look too shabby.

Cath@VWXYNot? said...

Excellent brain-straining post. I've heard the whole "the plane would fly with or without you on it so it doesn't make a difference" argument before, and while I do see the point, I tend to agree with previous commenters who've said that fewer passengers = less demand = fewer flights in future.

I buy carbon offsets for my flights, but I've no idea if it's doing any good. I usually choose to fund sustainable energy projects in developing countries, which I've heard is better than the "plant a tree" option.

Maybe one day Virgin will fly from Vancouver and I can feel less guilty knowing that the profits are going towards sustainable fuels research... Richard Branson rocks!

ruchi said...

Grad Green, I was actually thinking about this last night about the stand-by thing. If we want to calculate whether or car or plane would be better, we'd actually have to do it after the fact unfortunately. So, pick out the flight you would take. Then drive. Then see if your flight still took off. It it did, then flying was the better option. If it didn't, then driving was the better option. Unfortunately, it dosn't help in making your decision, but if we got enough data from people who did that, we could maybe make a reasonable guess as to which made the most sense.

Cindy, I believe technological innovations are coming in air flight. While the cost of fuel with cars is borne by the consumer, airlines operate in a very tight market. I wouldn't be surprised if some of the stuff we see as "science fiction" really is reality in 20 years or so. At least, that's what I'm dreaming of.

Hypoglycemiagirl, THANK YOU for bringing up this point which was missing from my post. The cost factor! Yes a train is the most environmental option much of the time, but it is also very, very expensive. If we want to make trains actual viable options for most people, we MUST bring the cost down.

Beany, thanks for the book rec. I'll email you a list of neighborhoods I like.

Cae, I think you're right about sustainable development projects being the better buy. I will look into those the next time I fly. What carbon offset company do you use?

Cath@VWXYNot? said...

It's been a while and I can't see the developing country projects listed, but I'm pretty sure it was this one.

I tried to claim my offset on my travel expenses once (I had to fly to a conference in Washington DC), but the company wouldn't let me, the cheapskates.