Everything good for you is bad for the environment

bicycle.gifIn a working paper entitled “The Environmental Paradox of Bicycling“, Karl Ulrich at the University of Pennslyvania reports that shifting people from their cars to bicycles offers almost no benefit to the environment.

We’ll dig into this paradox in just a second, but first a little background. Ulrich is the man behind TerraPass, the Wharton professor who challenged his students to bulid a viable business around consumer carbon offsets. Ulrich is also an avid cyclist himself and creator of a number of human-powered personal transportation products, including the Xootr Scooter and Xootr Swift folding bicycle.

Bicycles do have large first-order environmental benefits over cars as a means of transportation. Ulrich’s analysis considers the case in which a formerly sedentary person begins bicycling 10 km per day, 5 days per week. In this scenario, about one ton of CO2 is spared every year in the form of reduced fuel consumption.

This reduction in fuel use is partially offset by the increased food consumption of a cyclist. Although typically we think of food as carbon neutral — because the plants at the bottom of our food chain regrow after we harvest them — this view overlooks the fact that most of us don’t feed ourselves by hunting and gathering. The energy required to grow, harvest, process, package, and transport food to your nearest Whole Foods significantly outweighs the actual caloric content of your meal, by a factor of almost six. In other words, only about 15% of the energy we consume when we eat is actually in our food. The rest is contained in the fossil fuels used to bring our food to us.

But increased food consumption is a relatively minor effect when compared to the overall gas savings of cycling over driving. The real culprit in Ulrich’s analysis is the increased lifespan of people who ride bikes. Regular exercise helps you live longer, which points to an unsettling fact. One of the single best things you can do for the planet is to limit your time here.

Population is one of the primary drivers of energy consumption. And there are only two ways to increase the rate of global population growth: bump up the birth rate, or bump down the death rate. In effect, cycling does the latter. (If we look at the population of individual countries rather than the entire planet, immigration is a third way to affect population growth. We’ve previously discussed some of the energy implications of immigration.)

Ulrich estimates that every year of sustained bicycle use adds about 10.6 days to the average person’s lifespan, even accounting for the increased accident risk that cyclists face.

The result, in Ulrich’s analysis, is basically a wash. Each of us, simply by participating in the economy, uses a significant amount of energy. Bicycling rather than driving causes a large first-order decrease in the amount of energy a person uses, but the increased longevity of that person almost entirely negates the savings.

Interesting. But how well does theory map to reality? Personally, I have strong doubts about the practical implications of this analysis. The first issue is that most people who opt to cycle rather than drive cars are likely to be fairly fit already. These cyclists will see less health benefits on the margin than the hypothetical sedentary person, and therefore the first order CO2 reductions will dominate.

The second issue is subtler but possibly far more important. In Ulrich’s analysis, the population effects of cycling occur immediately (which is mathematically accurate in his hypothetical example). But I strongly suspect that the actual demographics of bicycle usage mean that the population bump from improved fitness won’t be seen for a number of years. In effect, riding a bicycle shifts energy consumption from today to an unspecified point in the future.

In private communication, Ulrich ballparks the delay in the population bump as maybe ten years, which he points out is an insignificant amount of time when compared to the climactic changes that are already underway. True enough, but ten years could be long enough for highly significant changes to occur in the energy intensity of our lifestyles. If, for example, in ten years all of our electricity is produced by wind (yea!) or coal (boo!), shifting our consumption into the future will have real consequences for our rate of carbon emissions.

My advice: keep cycling, certainly for your health, and for the environment too.

Update: Ulrich’s paper got picked up in Andrew Leonard’s How the World Works column in Salon. Fun read, although Leonard’s main complaint seems to be that he doesn’t really like the conclusion of the paper.

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  1. Jen - July 18, 2006

    Was there any accounting for pollution if current consumption trends continue? I woke up to a smog alert and opted not to ride my bike to work. It seems to me that if I had, the physical benefits of riding would have been offset by the detrimental effects of pollution on my lungs.

  2. Adam Stein - July 18, 2006

    Nope, effects from smog are definitely out of the scope of the article, which just looks at the generalized health benefits from physical activity.

  3. disdaniel - July 18, 2006

    So according to this theory, wars may be good for the environment?
    I hope no suicide pacts are formed based on these findings.

  4. Adam Stein - July 18, 2006

    It’s important not to overplay this tension between human well-being and the environment, but it’s probably not news that such a tension exists. It kind of goes without saying that humans aren’t generally all that great for the environment, at least in their present numbers. No people, no problem. It also goes without saying that there’s a lot of moral good in having a happy, healthy human population on the planet. The trick is having both a happy, healthy population of humans and a healthy environment. In other words, war fails the test as an effective greenhouse gas abatement mechanism.

  5. Anonymous - July 19, 2006

    1. were i to switch to bike riding as opposed to driving my car (which i am considering, trying to factor in my small children), i would likely stop going to the gym, thereby transferring my fitness level from gym-based to bicycle-based. hence, my longevity might not be increased substantially, nor would my caloric intake.
    2. since many americans (myself included) tend to overeat over the course of their lifetimes, it would seem likely that anyone who begins biking in an unfit state would not need to increase their caloric intake. they might have more impact by living longer, but not necessarily by eating more.

  6. Adam Stein - July 19, 2006

    Yep, correct on both counts. In fact, the paper does address the fact that switching people from other forms of exercise to bicycle commuting is a clear net positive for the environment. And there is another academic paper that has been published suggesting that drawing down the energy stored in fat on Americans’ bodies might be a good greenhouse gas mitigation mechanism.

  7. Bill Becker - July 19, 2006

    Ulrich to World: Fight climate change. Die young.

  8. Kamal - July 19, 2006

    It would seem that, in my opinion, living longer in an environmentally conscious manner would be much more beneficial to the planet than living a shorter life under our current environmentally destructive practices.

  9. jessie - July 19, 2006

    What about bicycle riders being mentally and physically healthier therefore not needing as much healthcare (ie: medications for depression, diabetes heart conditions, etc). How much energy is required to produce pharmaceuticals?

  10. Windowdog - July 19, 2006

    That is simply the most awesome thing I have read in weeks…. hahahahahahahahahahaha, its like it came right from the pages of a Douglas Adams book.
    We need to eat more ice cream for the sake of the planet. Ben and Jerries is really far more eviromentally friendly then I even thought. Oh god I have a prediliction for nihilism since college, so maybe its just me, but this going to have me chuckleing for weeks on end.
    Maybe Agent Smith in the Matrix, or the bad guys in Rainbow Six weren’t so far off…
    My cubicle mate, who has no interest in anything but his hummer and the stock market, just chimed in that someone is going to start popping off nukes in the next 80 years anyways, so we all need to chill out a bit.
    God that is just simply simply brilliant. Gluttony for a better tomorrow. I could be President with a platform like that.

  11. Terry - July 19, 2006

    Well as any economist worth his salt can tell you, anything can be proved by numbers. The air we breath in contains about 0.04% of CO2. The air we exhale contains about 5% CO2. According to some numbers I found by Jerry Hannan, each person puts out 445 liters of CO2 per day or 704 pounds per year. The human population of the earth is around 6.4 billion. So we personally put 4.5 trillion pounds of CO2 in the air each year. If we assume 10,000lbs CO2 per car then we put out the equivalent of 450 million cars worth of CO2. There are 600 or so million cars on earth. So we could offset 75% of the CO2 pollution of cars if we simply stopped breathing. A fallacious argument of course since we all, (except for MacDonalds customers), eat food from renewable resources. It is interesting in that is puts us in perspective and agrees completely with what is implicit in Ulrichs detailed numerical analysis. We can solve the carbon dioxide issue simply by dying.

  12. Erin MacDonald - July 19, 2006

    In the immortal words of South Park
    We have to think about THE CHILDREN!
    Riding a bike a lot is correlated with a low sperm count. http://www.nym.org/healthinfo/docs/067/doc67causes.html
    And longer life spans correlated with having less children, as briefly mentioned here: http://www.bioethics.gov/background/agingresearch.html
    For these two reasons, riding a bike can be correlated to a decrease in population growth, which would surely be good for the planet.

  13. Anonymous - July 19, 2006

    The article fails to account for the high likelyhood of cyclists getting hit and killed by cars, especially if they are not wearing a helmet.
    So, for the sake of the environment, do bike to work, but don’t wear a helmet,

  14. Alex Censor, M.S. - July 19, 2006

    I believe some responders have already alluded to this, but there is one flawed assumption in his analysis: His scenario involves all the sedentary people getting off their office chairs and out of their cars and starting cycling to work and the local shops. In reality, if by the most utopian projections of the most avid cycling promoters we somehow got 25% of the US population replacing half their car miles with bicycle miles in that group we would find that those who are already physically active and have the best life-span projections far out representing the sendentary folks. As one fellow suggested — if he were cycyling more he’d be spending less time and resources in the gym. And he’s already among those with the long lifespan projections.
    As to the implied question “what would you do to mitigate the enviromental effects of having the entire USA sedentary sub population halfing their driving by by cycling where ever possible?” my reply would be “That’s a problem I’d LOVE to have to deal with!”

  15. Jack Bergstrom - July 19, 2006

    To think that converting from cars to bicycles is a good option for many of us is simply not practical. However doing things as I have already done is. I know that most people think I have lost my mind. I drive a Ford ranger with a 4 cylinder engine I don’t exceed 55 mph and I removed the stock bed and put a flatbed on it that is made of a much lighter material this raised my miles per gallon from 24 to 31 miles per gallon. I am also working to develop a commuter vehicle that will be powered by a 35 horsepower engine that should get over 45 miles per gallon and the engine that I have chose is capable of operating on diesel or biofuels. I am challenging all people out there that are concerned about the earth to stop talking and start doing something you don’t need SUV’s or big cars and it is past time that people started to use some common sense 95% of the cars I see on the road have one person in them a motorcycle or a two seater car would not only be more practical but would make sense. So quit complaining and start taking action!!!!

  16. Alex Stange - July 19, 2006

    There’s another subtle component to more people bycycling: lower birth rate. My cycling friends tell me that there’s a common problem for men who ride a lot, in that their hard seat pressed against the blood flow to their groin day after day can sometimes cause impotence. I guess they have a pill for that now, but I’m just saying, it’s another factor.

  17. McKay - July 20, 2006

    I applaud Jessie’s point, and was thinking the same thing prior to reading her perspective. How does one begin to account for the energy use and CO2 production for higher health care costs for unhealthy people?
    Comment by jessie @ Jul 19, 2006 8 AM
    What about bicycle riders being mentally and physically healthier therefore not needing as much healthcare (ie: medications for depression, diabetes heart conditions, etc). How much energy is required to produce pharmaceuticals?

  18. veektor - July 20, 2006

    — Adam (6) and Kamal (8) have good points — cyclists and other fit people are likely to be happier and generally more environmentally aware than those who don’t (although if you need to drive a car to get to your cycling areas, as many mountain bikers do, this cancels things out). As an avid hiker, I have to confess to feeling guilty about driving to distant areas to enjoy the woods.
    –The article is a good tongue-in-cheek example of being able to prove almost anything you want by making the right (or wrong) assumptions. Things aren’t always as obvious as they seem and there is practically no such thing as a closed system or a simple problem. On the other hand, some solutions surely seem better than others.

  19. Ulrich Nehls - July 21, 2006

    An uncle of mine used to make a similar point about the environmental benefits of cycling.

    He said that when he’d bike his usual five-miles trip to the next town, a higher number of car drivers might be forced to slow down and accelerate again, since they would have to wait before overtaking him due to oncoming traffic.

    So, he said “I do doubt whether there is an overall benefit from my bike use.”

  20. Claire - July 22, 2006

    This is a very good paper for one reason. The author takes the time to think about the complex relationships inherent in any issue. I am so very tired of hearing problems and solutions discussed in such simplistic ways and welcome someone who presents an issue in a “systemic” way. I’m not saying the paper has covered everything or even that it is correct in its assumptions, but that it is an excellent example.

  21. Anonymous - July 22, 2006

    he overlooked the reasearch that cycling may increase impotence in men…so therefore the lower death rate maybe offset by a decreased birth rate.

  22. Scott Rodamaker - July 26, 2006

    First down with the Ulrich myth. Some fatty gets off the couch and rides 6 miles a day, unfortunately for them they will remain fat. The added caloric intake would be around 150 calories. What if they drive a Prius or electric car, compared to the average 21mpg vehicle? Opps, contradicting my own argument.

    Put some real numbers out here like 20-30 miles a day which is a common bicycle commute. About once a week I rummage around the fridge and find old rotten food, which if I had ridden 200 miles that week may have gotten eaten rather than tossed away so zero impact, and dont forget a gargage truck has to come pick up my trash, those get great mileage right? Debating from one side of an debate is lame, get out there and ride your bike, sell your SUV, and vote for someone who doesn’t lie to us constantly.

  23. Anonymous - July 26, 2006

    Other side effects of bike commuting (some alluded to above):
    a slight decrease in traffic volume which may affect congestion, thereby increasing the communitie’s average fuel economy.
    an increase in the participant’s active life, while not such an increase in their total lifespan would decrease medical care requirements which are energy comsumptive.
    time spent cycle commuting is time not spent on more energy consumptive activities
    some percentage of people drive to the gym to workout, and drive to work. Combining you commute with your exercise is a net time savings, plus is more beneficial to the environment.
    These may have been covered in the study. I didn’t read it, so what do I know? Cheers!

  24. grewal - September 6, 2006

    population growth create much types of problems

  25. Anonymous - March 9, 2007

    The Swift Folder was created by Peter Reich and Jan VanderTuin. Xootr is just manufacturing them.

  26. michael - April 30, 2007

    [Ed. — Comment deleted. And it was so close to making it in. Why end with the childish ad hominem attack?]

  27. Mike Jones - February 1, 2008

    yo mane… who cares about the enviornment.. all of you nerds need to quit trippin.

  28. brooke - May 11, 2009

    “One of the single best things you can do for the planet is to limit your time here.”
    Do you actually believe this? Seriously? Don’t you think your existence could benefit humanity and the planet? This line of thinking–people are bad and need to go–seems over-simplistic and is total eugenics. I do not like it.