Image: Graphic by Jen Christiansen
Hybrid cars have become so eco-friendly they now trump at least one form of human locomotion. Alberto E. Minetti, professor of physiology at the University of Milan, along with his master’s student Gaspare Pavei, compared the CO2 emissions of four men walking, running and biking with the emissions of a hybrid vehicle carrying those same four men. The scientists found that four men would release more CO2 by jogging than if they boarded a hybrid car. (On average, four women jogging would release less CO2 than if they rode in a car because of their lower body mass.) The lesson: next time you and three male friends are late for the movies, don’t run. Hail a hybrid taxi.
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21 Comments
Add CommentDoes the carbon dioxide total with each vehicle used include the CO2 released by the four men sitting at rest within the vehicle? From the earth's point of view,it should, or the results are skewed by the omission.
Reply | Report Abuse | Link to thisGood point traredon. Nor does it likely count the CO₂ required to manufacture the vehicle in the first place factored in over the lifetime mileage of the vehicle. On the flip side, it probably beats the heck out of having four horses, which produce methane and CO₂ even if you aren't using them, not to mention other forms of pollution.
Reply | Report Abuse | Link to thisI agree with traredon's point. Also, I would like to know what the assumptions were for speed and distance traveled. Hybrid technology doesn't do much good for highway driving.
Reply | Report Abuse | Link to this@Soccerdad, I was wondering about speed as well. Already in the chart, they assume different speeds for walking and cycling. These results defy common sense. Not that that necessarily negates anything, but the omission of a link to the source research doesn't help with credibility.
Reply | Report Abuse | Link to thisOf course, the above comments ignore the fact that people and horses are exhaling carbon dioxide as a result of metabolism. Then they both defecate fertilizer and urinate nitrogen rich fluid that promotes plant growth. Plants then absorb the carbon dioxide during photosynthesis. The people and horses then eat the plants, metabolize the byproducts of digestion, and exhale, and so on.
Reply | Report Abuse | Link to thisThis, my friends, is what we call a balanced carbon budget or a closed loop carbon cycle.
Burning fossil fuels extracts carbon that was buried and puts extra carbon dioxide into the atmosphere. This is not a closed loop cycle and it is not sustainable even if the excess carbon dioxide caused no greenhouse effect. Sooner or later you run out of fossil fuels.
The month is not yet over...April fools.
The whole study is completely irrelevant because the CO2 the humans are exhaling is part of the short term carbon cycle and does not add to the total CO2 in the atmosphere. What is being released by the vehicle is long-term stored CO2 which IS adding to atmospheric CO2 levels.
Reply | Report Abuse | Link to thisThe problem with saying that people and the food they eat are part of a closed loop carbon cycle is that every step of food production is heavily dependent on fossil fuels. The machinery to plant and harvest the food runs on petroleum. The fertilizer that is applied to the fields is very energy intensive to produce. After harvest the food is processed and transported possibly thousands of miles before it finally arrives at your local supermarket.
Reply | Report Abuse | Link to thisReally though, this is getting off subject. It just shows that it is really a matter of how deep you want to look into it. The authors of this study were looking at the topic in the most simplistic way possible and they made an interesting finding. I'll take it at that.
Assuming that it's an hour walk to the movie house, I find it VERY hard to believe that jogging for 10 minutes and standing around for 50 minutes produces much more CO2, and that bicycling for 4 minutes and standing around for 56 minutes produces much less. I want a competent chemical engineer to audit the numbers, because I've seen too many wackos writing poorly considered articles in the popular press.
Reply | Report Abuse | Link to thisI might believe that riding an electric golf cart might produce less CO2, because the human body is not an especially efficient source of motive force. That's why the horse collar did so much to end slavery (not that slavery is completely gone yet....)
It is good to know!
Reply | Report Abuse | Link to thisBut when you drive a car for 100 miles is not so far and you go for it. When you have to ran 100 miles - not sure :)
Possibly, this is the main reason, why 10-20% fuel economy is good but not critical on the country scale.
Sci Am,
Reply | Report Abuse | Link to thisI always find myself on the same side as anti-environmentalists when journals publish such claptrap:Don't publish mistakes, or we lose credibility. The difference between fossil carbon and food carbon is the most damning to the premise of the article, which I assume is implied by the title.
Perhaps Pavei et al were confused in methodology by the difference between pollutants that are only locally significant, such as many smog-forming emissions, and those that are globally significant, in this case CO2. Concerning the former, a Hummer is "cleaner" than a lawnmower. Thus, if CO2 were some noxious gas, a hybrid might be cleaner than four people jogging. But it isn't.
Each article like this sets the cause back years by confusing the public.
This article does not say anything that is not already well known - that human energy results in far more CO2 than energy from gasoline powered internal combustion engines.
Reply | Report Abuse | Link to thisIn fact, this article minimizes the CO2 impact of human physical activity. It fails to take into account the CO2 generated to produce the excess food consumption required to fuel an active as opposed to sedentary human being.
Far from what is claimed in some of the comments, there is no closed loop. Agricultural production sufficient to feed 7 billion people requires large amounts of energy, for farm equipment, fertilizer production and delivery.
I left out other major contributors to the CO2 cost of exercise - food preparation and cooking serve to further boost the CO2 cost of human energy far over that of internal combustion energy.
Reply | Report Abuse | Link to thisTotally think the manufacturing cost of the vehicle has to be considered too.
Reply | Report Abuse | Link to thisBut what about the carbon dioxide required to make the people? :-)
Or is the existence of human life an end in itself? I think so.
"human energy results in far more CO2 than energy from gasoline powered internal combustion engines"
Reply | Report Abuse | Link to thisNo, it shows that it takes about four humans to match the CO2 output of even an efficient gasoline engine, on a per mile basis.
So, if you drove 30 miles round trip to work and back, and then run 3 miles for exercise, then your car produced about 120 times as much CO2 as your breath did. If you drove an SUV that got only 15 miles per gallon, then it is more like about 240 times as much.
That does not include the CO2 that was produced making and delivering the gasoline, or the CO2 produced providing you with food.
In Mad Max Beyond Thunder Dome, the question arises from where does menthane come from? Methane cometh from pig ***t. We also know the amount of gasses cometh from dung beetles, now we know that four guys jogging will create more co2 than a hybrid car. So, if four guys will produce more co2 than a hybrid car, what about the New York or Boston manathan? Are marathons responsible for the rise in co2 levels and the global warming of the earth? If the runners become couch potatoes then there would be less co2 in the world. But! On the other hand, women joggers produce less co2 than jogging men, so it is safe for women to jogg, because jogging women produce less co2 than jogging men do. What about other sports like basketball, baseball, football, or hockey? The bigger the man the bigger the toot?
Reply | Report Abuse | Link to thisScientific American is definitely dumbing down science by allowing this kind of facile, snappy, idiotic "sidebar" article without mentioning the enormous footprint that the manufacturing and the infrastructure of cars (no matter what fuel is involved!) has on earth's ecosystems. I have a print subscription to Sci Am which I am considering cancelling because of this kind of rubbish, not to mention the sell-out, massive, double spread advertising for cars and financially crooked companies like Goldman Sachs, now so common in this magazine.
Reply | Report Abuse | Link to thisIt all really comes down to the basic fact that the best way to cut down on over all consumption is to reduce population. Anything else is just a shell game.
Reply | Report Abuse | Link to thisexcellent point...
Reply | Report Abuse | Link to thisUnless this is a hybrid diesel, the fuel used is non-renewable whereas the food eaten by the men is renewable. As others have stated, it does not take into account the CO2 taken to produce the vehicle or the fact that the men are also breathing while sitting in the car.
Reply | Report Abuse | Link to thisIt would be interesting to know how much CO2 is taken to produce a hybrid and, if the car were a bio-diesel hybrid, how far you'd have to drive it for the 8gm CO2/km savings to net out.
The trap here is that the author of the article implies that there is something bad in CO2 emissions per se.
Reply | Report Abuse | Link to thisAccording to the author, "eco-friendliness" seems to be related to lower CO2 emissions, without any regard for who generates those emissions. It seems to be the same if the emissions are made by a man, or by a machine made by mining minerals, using fossil energy for building this machine, and more fossil energy for powering it, and polluting all the way through the process.
Comparing CO2 emissions from such dissimilar sources, and pretending to draw conclusions from it, makes no sense at all.
By a similar line of reasoning, the unmanned traveling of the hybrid vehicle senselessly around, would be much more eco-friendly than when 4 CO2 emitting passengers are sitting on-board. The lesson: next time you and three male friends are late for the movies, hold your breath, stay at home, and let the hybrid vehicle enjoy the movie for you.
Dear All, I hesitated to reply to all your message about Anna Kuchment's short on our work, because the original paper was not out yet. Now the magazine can be found at :
Reply | Report Abuse | Link to thishttp://www.physoc.org/site/cms/contentChapterView.asp?chapter=151
and the full article at:
http://www.physoc.org/uploadedfiles/documentlibrary/824.pdf
On specific matters, I want to claim that the whole study has been done to ascertain that modern technology of transport build vehicles that consume less energy (and emit less CO2) than the 4 transported persons. It was far from my intention to state that we don't have to run because CO2 is higher than using a (hybrid) car in town.
As far as renewable energies vs. fossil ones are concerned, only grabbing an apple from a tree is a green process, but most of the food processing chain relies on petrol, thus on fossil fuels. We conducted a simple experiment where we measured that almost 600 Kcal of methane are necessary to cook pasta that will provide less than 300 kcal to our body. Is this a green, renewable process?
Alberto MInetti - aminetti@me.com