I bought a bicycle yesterday. It is my intention to ride it to work as much as I can this summer/fall, mainly for health and fitness reasons (and to a limited extent savings on gasoline). Curious, though, what benefit to the environment will this provide? I’m interested in the final answer given the specifics of my commute - but of course welcome generalized comments/discussion.
The facts, ma’am:
[ul]
[li]My round trip commute is 43 km.[/li][li]The round trip takes 35 min by car.[/li][li]The round trip takes 127 min by bike.[/li][li]My car burns gasoline at the rate of 10.7L/100 km.[/li][li]My VO[sub]2[/sub] max is 51.5 mL/kg/min.[/li][li]My bike and I together have a mass of 102 kg.[/li][/ul]
(trivial note: I calculated the bike will have paid for itself in gasoline savings after 51 trips!)
Assumptions
[ul]
[li]The measurement of benefit to the environment is best expressed as how much less CO[sub]2[/sub] my bike and I exhaust compared to my car[/li][li]My oxygen consumption is roughly equal to the CO[sub]2[/sub] I exhaust (I do stand to be corrected)[/li][li]I apply the VO[sub]2[/sub] max rate to my biking, even though it was measured while I ran on a treadmill[/li][li]I’m sure I’m making more than a couple hidden assumptions…[/li][/ul]
So given the above, per round trip I exhale a maximum of (51.5 * 102 * 127) ÷ 1000 = 667.1 L of CO[sub]2[/sub].
(I just noted that the 127 minutes is based on a speed far less than required for me to reach my VO[sub]2[/sub] max, but I’ll fix that later - I want to send this so I can get back to work )
I don’t know how to measure (or estimate) what the car exhausts.
And what of the total impact? (rubber residue on the roads, other materials exhausted, the energy cost of refining the oil)? Any ways to express/estimate these?
You also have to consider the CO2 impact of the additional food you will consume, now that you are expending additional energy bicycling.
I glanced at an article a few weeks ago that suggested this would significantly offset the CO2 savings of commuting by bike. I was distracted by other things, and didn’t process the details. It seems a dubious claim to me, but I wish I could find it again.
Don’t forget that the exercise you get by riding your bike may cause you to live longer, which means more time spent consuming our planet’s precious natural resources.
I find it unlikely that the energy savings gained buy not taking your automobile to work are going to be greater than the difference between methods of taking your body back and forth.
I haven’t seen the article, but my WAG is that such calculations use fishy math . . . like including the CO2 produced in transporting food to your grocery store, but comparing it just to the amount of CO2 produced by your car (ignoring that gasoline also has to be transported).
There’s simply no conceivable way that riding a bike is as bad environmentally as riding a car, for the simple reason that in one case you have the extra cost of transporting a huge lump of metal (the car itself) around with you.
The /kg in the VO2 term is your body weight, and does not include your bike, if I understand correctly. Using the term like that doesn’t take into account added efficiencies of the gears, either.
No. You’re breathing more than you would if you weren’t biking. The carbon has got to come from somewhere.
It comes from food, which is either plants or meat made by animals eating plants. Either way, the carbon comes from plants, which means it came from the air, which means you’re just recycling it.
Burning gasoline, on the other hand, takes carbon that’s been stored deep underground for millions of years and adds it to the air.
I think this is right. The division by body weight is done to produce an index that’s more directly comparable among people of different sizes. I think it would be more appropriate to use your absolute VO[sub]2[/sub] max in this calculation.
Also, source of the carbon being exhaled aside for the moment, I don’t see any consideration being given to your resting rate of respiration. Unless I’m grossly misunderstanding what VO[sub]2[/sub] max represents, you need to take into account that you’re breathing during the 127 minutes, regardless of whether you’re biking or driving.
This is the mistake. All the CO2 your lungs exhaust comes from food, which takes exactly the same amount of CO2 out of the air when it’s grown. So overall, your lungs+farms are going to balance down to zero carbon emissions over the course of a year.
As opposed to the CO2 coming out of the tailpipe of your car. That comes from gasoline which comes from oil that’s been underground. So driving does overall add CO2 to the air.
On preview, since the point’s been made, let’s add some numbers.
Most estimates of the fossil fuel cost of food calories are for ethanol; about the highest I’ve seen is 4 fossil fuel calories used to grow 1 food calorie.
So if your car gets better than 90 km/liter[228 mpg] after including the fossil fuel used to extract, process and transport the gasoline, then you should start considering whether other factors than CO2 emissions would be important, otherwise, biking wins.
Another factor is that you’ll be saving wear and tear on your car. It takes a LOT of resources and energy to make and maintain a car, and disposing of the used-up car has an environmental impact as well. Prolonging the useful life of your car is good from a green standpoint.
Of course, this will be somewhat offset by the fact that you’ll be putting wear and tear on the bike.
I’m not sure if we can quantify these factors, and it is far from the most important factor here, but I thought I’d throw it out there.
It’s also worth noting that CO2 is not the only thing coming out of that car’s tailpipe. CO, carcinogens, particulates, etc… are all part of that stew.
Does this not assume that there is a direct relationship between the amount Nature’s Call eats and the amount of photosynthesis that occurs? Uneaten food is wasted, uncultivated land grows other plants which may act as carbon sinks (e.g. wood) and probably a load of other factors. It is NOT important where an individual kg of carbon came from, only the balance between rates of release and capture.
Not at all this is a basic flaw (and one that is oft’ repeated by people who show know better).
The CO[sub]2[/sub] that is released by me when I cycle to work (which thanks to a new job I now do ) WAS ALREADY IN THE ATMOSPHERE. Prior to being eaten by me, it was part of a plant (or animal), and, prior to being bound up by photosynthesis, it was in the atmosphere. This is the natural carbon cycle, carbon is in the atmosphere, it is then absorbed by plants (by photosynthesis), eaten by animals, then released back into the atmosphere via respiration. That very simple high-school biology.
The carbon my car releases back into the atmosphere was not bound up last month, or last year, it was bound up over billions of years, and deposited gradually into the earth’s crust. For all intents and purposes its NEW carbon.
There is an intrinsic difference between the two, that means that, yes, it is VERY MUCH GREENER TO CYCLE TO WORK.
As long as we till fields with diesel-powered tractors and ship food by truck and train, then increased caloric intake has a net effect on atmospheric carbon. Increased food production requires increased fossil fuel usage. In fact, I believe that there is a substantial multiplier, ie, that it takes, say 10 calories of fossil fuel to produce a single calorie of food. So, yes, the carbon you exhale isn’t directly impacting atmospheric levels, but the gas burned to produce the food you eat sure is.
However, I’m not at all convinced that the net result of cycling to work really will increase caloric intake. Sure, it will in the short term, since you’re burning more energy. But in the long term, you’ll probably be healthier, thinner, and eat less than you would have. So it’s only bad for the environment if you cycle for a while and then give up. How’s that for motivation?
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