AskPablo: Planes, Trains, and Automobiles

ptauto.jpgThis week on AskPablo we will be looking at various transit modes and their relative ecological impact. I have received a few related questions on this matter so I will try to address them all. Please make sure that you submit questions for the next few weeks. Otherwise I will have to start making stuff up…
Let’s start by looking at a few transit modes. We already covered the “beef-powered cyclist” a few weeks ago so I would revisit the greenhouse gas impact of cycling. According to one source a single-occupant vehicle travelling at highway speeds emits about 0.101 kg of CO2 per passenger-kilometer, or about 1kg (2.2 lbs) per 10km (6.2 miles). We all know that there are many ways to improve this. You could drive a hybrid (But is that really better, given the batteries required? Maybe some other time…), carpool, keep your tires inflated to the proper pressure, keep your car maintained, etc.

A bus travelling at the same speeds emits around 0.041kg per passenger-mile, or 2/5ths as much as the car. Unfortunately there are some setbacks to this transit mode. Many of us don’t like sitting next to smelly people named Earl (no offense to any Earls that might be reading this) for 16 hours on a Greyhound bus from Bakersfield to Salinas. Travelling by train is even more efficient, at least as far as carbon emissions are concerned. Sadly, unless you are in Europe, it will probably take you about twice as long to get where you are going.
Assume that we are the jet-setting corporate type. What is our impact? Well, it’s somewhere around 0.214kg per passenger-kilometer, over twice the impact of driving. There are several factors with flying though. It was recently discovered that flying at night does more damage to our environment so no more red-eye flights, OK!? Also, the greatest amount of fuel is consumed during takeoff and landing when the wing flaps are extended to produce maximum lift at relatively low speeds. So, if you are flying across the country with multiple layovers mother earth will be angry with you. And you don’t want to upset your mother…
So, in summary: walk or ride your bike, take mass-transit or carpool, and fly during the day with as few stops as possible. When you can’t eliminate a trip, don’t feel guilty. It is very easy to offset your carbon contribution these days. Just last week I offset all of my 2007 carbon emissions of my vehicle for a mere $40 (Yes, I have a car, but I waited until I was 25 before I got my first car and rode my bike everywhere before then, OK?) using DriveNeutral . You can also offset other travel and lifestyle emissions through DriveNeutral, TerraPass, and others.
After you have offset your various carbon-related guilt please do me a favor and think of a cool question to AskPablo. See you next week!

17 responses

  1. Pablo Hi,
    At we plant trees for airline travellers who want to reduce their carbon footprint. Our project is based on the simple idea that as the tree grows it gradually re-absorbs the CO2 released by the flight. Because we all share the one atmosphere, people use the service from all over the world. A Beech tree planted up here in the mountains of Wales can fix 1.25 tonnes of CO2, roughly equivalent to a return economy flight, London – New York.
    It only takes 125 years.

  2. Pablo –
    When looking at my ecological footprint, I’m only able to view impacts from my own actions in terms of CO2 emissions. What about all the impacts of the manufacturing of the goods I buy? Can life cycle assessment (LCA) fill in the footprint picture more completely?
    I was playing with the EIOLCA website to get a sense for life-cycle impacts of production. This is a geeky thing to use for a typical consumer, but I thought it was very helpful.

  3. Hi Pablo,
    My question is about home air filters. First, do they work? What models are best based on effectiveness, energy efficiency, ease of use and cost? Most appliances can start off cheap but end up expensive with replacement filters. I’ve heard some are bad because of ozone technology is that true? What about air washing (uses water)? All too confusing. I live by a busy street so I know all sorts of particulates are in the air (you can see it accumulate on the windows)and would like to get a filter if a good one exists.

  4. There are a zillion impacts of single car ownership that go way beyond CO2 emissions… not that single car ownership is going away. We need a mixed bag of options for people.

  5. Offsetting carbon emissions using trees is a very interesting science. Recently some people have cast doubt upon it because some trees emit more methane than they sequester carbon but some trees are actually quite good at undoing our damage. According to the calculator on the site a 3000 mile flight emits 1,920 lbs of CO2 and they estimate that it would require 299 Sugar Maple trees per month to recapture that carbon. This is equivalent to a single tree that is allowed to grow for 25 years, probably the lifespan of a tree farm crop. The main difference between carbon sequestration with trees and with a carbon market such as the Chicago Climate Exchange is that the former works over a span of several years, while the market is essentially immediate. I don’t quite know if it matters either way and I would welcome discussion on that from our readers.

  6. Jules, that is a great question. The people at the Wuppertal Institute in Germany, where MIPS was developed, did a MIPS analysis for record Company EMI as part of the Digital Europe project. The analysis was very similar to your question. They compared buying a cd in a store, ordering a cd on-line for mail delivery, and downloading music. With DVD rental you have the same three options so the study is very relevant. Not surprisingly the result was, in order of increasing impact: downloading, buying on-line, and driving to a store.

  7. Pablo, The latest evidence suggests that the positive carbon sequestration effects of trees outweigh the negative methane production effects by a factor of ~100 times. See this link from CSIRO – Australias well respected National Science Academy.,,.html
    I know I’m biased in favour of the trees but since the worlds forests are currently re-absorbing 20-25% of all human CO2 emissions they are actually doing a pretty fantastic job of cleaning up after us.
    Last year we lost something like 17 million acres of the forest that is doing this planetary purification job.Every second of every day, every tree is patiently using solar energy to clean up our mess.
    Ru from Treeflights.

  8. Regarding your discussion on trees as a sequestration method, I think this is a common misunderstanding: True, when you plant a tree it will sequester CO2 for the duration of it’s life (asside from some emissions, depending on the type of tree). However, unless you are going to take the tree when it dies and seal it up or sink it to the bottom of the ocean, it will decompose, and release the carbon — much as methane. So where is the benefit? Climate change is a long-term game, not just for the lifetime of one tree.

  9. oh – one more note: of course the exception to what I said above is slash-and-burn tactics which are reducing forests big time. That is obviously an unreplenished source. It not only burns the vegetation releasing all the carbon but also permanently transforms the land use to one that will absorb nothing in the future.

  10. These are very valid points. It is hard to predict long into the future but our forward plan for the trees goes like this. Leave in the ground for as long as possible as standing living carbon sinks. (There is an oak in estonia that is 1500 years old.)
    Then harvest for construction timber(all the species we plant are types that can be used in this way), with the right preservation techniques this should ensure that the bulk of the CO2 is retained in situ for another few hundred years. After this we want to bury the timber(exactly as you say!) either in the sea or in the peat bog that they are growing on. In these anaerobic conditions we believe that flow back of CO2 to the atmosphere will again be minimised. (Think of how well preserved the timbers are, on those viking longships that were brought to the surface and are now in museums in Britain. Once dealt with in this way the original land that grew the trees will be replanted and the process begun again.
    We think that in the future there will have to be ‘sequestration farms’, like this covering vast areas of our planet to deal with the Co2 that we are so liberally releasing at the moment.
    This is a precis of a vision reaching far into the future and I’m not even sure what I’m doing tomorrow. We are going to need all our reserves of foolish optimism to get thru this problem.
    We are setting up the Treeflights Trust to oversee this process and hold ownership of the land on which these trees and their successors wiil grow.

  11. How will DriveNeutral account for the new, national Renewable Fuel Standards, which started in 2006, when estimating a participating driver’s CO2 emissions? I understand the law permits the content of ethanol to vary from state to state as long as the national standard is met/ The result is that some states may contain no ethanol and other states can have as much as possible. If not accounted for CO2 emissions in states with ethanol will be overstated.

  12. A question for you: Have you seen any data indicating what fraction of carbon is emitted for an average western person (o.k., maybe not average, say American) by category? The only data I’ve seen was patial, like travel by car, flight, heating, but doesn’t usually include indirect impacts like consumer goods (co2 per $ spent?).
    Thank you,
    H. Hammer

  13. Hi Pablo,
    I have to plan a trip and I want to choose the mode of transportation that would be most eco-friendly. I just calculated the effect of a plain ride and the effect of a bus ride to and from the same desination, using The result said that the bus ride would be slightly WORSE! I thought a plain trip would be worse.
    do you have any recommendations on what i should do? bus or plain? do you think the calculator might be wrong?

  14. Carbon trading is nonsense since its a forward oriented approach; in other words, whereas the climate change problem is, first and foremost, all about trying to do something about all the carbon already released, the credit system is oriented toward current and future, carbon emissions. Moreover, “carbon credits” are a kind of smoke and mirrors shell game, which involves nothing more than paying for the “right” to emit carbon that would otherwise not be emitted anyway: the credits are only up for sale because the holders of those credits do not need them, since they are not emitting carbon. In other words, we should be aiming toward having the carbon seller not emit carbon, as well as the person who would otherwise be buying their “credits”, using public transport, to get around, instead of giving them the idea that a car is ok, so long as they pay a “guilt tax”. Carbon trading is not the answer; rather its just another ploy by the irresponsible market forces which have led us into the current morass. Profiteering caused the problem, so there is no reason to believe that it offers the solution. Rather, the answer involves a fundamental shift toward a re-orientation of our priorities as people and as societies: less consumption, less selfishness, more simplicity, and more respect for earth, and for all the beings which inhabit it.

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