Bicycles and CO2

Papa Don commented a few posts back about the role of bicycling and reduction of CO2 emissions. He brought up an interesting idea: does riding a bike matter in reducing carbon dioxide?

To answer this question, first we need to discuss the Carbon cycle and the methods of carbon release. The thing is, there are two ‘branches’ of the carbon cycle. The Slow (ie, geological times scales) and Fast (ie, Physical/Biological time scales) Cycle. Like any of these cycles, we are assuming it is a closed system, where mass is conserved. Thus, the ‘cycle’ in the phrase Carbon Cycle, is simply the flux of mass between different elements within the system.

In the geologic time scale, carbon in the atmosphere reacts with seawater by means of a buffered equilibrium reaction (g=gas, aq=aqueous, l=liquid):

  1. CO2(g) <–> CO2(aq)
  2. CO2(aq) + H2O(l) <–> H2CO3(aq)
  3. H2CO3(aq) <–> H+(aq) + HCO3(aq)
  4. HCO3(aq) <–> H+(aq) + CO32-

where the available carbonate (end of step 4) likes to react with Mg2+ or Ca2+ producing Dolomite or Limestone over millions of years. This limestone precipitation (ie, carbon storage) occurs in temperate, non turbid waters like the Bahamas. During the geologic past, much greater portions of the worlds oceans were favorable for carbonate precipitation (eg, most of the mid North American continent during the Mesozoic). The massive amounts of carbonate platform are eventually buried by other basin sediments, and/or subducted under continental plates, creating huge stores of underground carbon in the form of fossil fuels and gases.

In addition to the geologic carbon cycle, there is also a physical/biological cycle that reacts much quicker (over 100s-1000s of years) in the form of plant and animal respiration and photosynthesis. During photosynthesis, plants take in CO2 and produce sugars as a form of energy for the plant cells to do work (metabolize). Also, animals respirate CO2 when we break down those sugars (carbohydrates) to make our energy. Generally, the Biological carbon cycle moves 1,000 times more carbon per year than the geological carbon cycle.

At this point, we have two branches of moving carbon, that are interacting, but on a basis which maintains an overall dynamic equilibrium over time.

Now, here is where anthropic impact plays a role. As we consume fossil fuels, we are bridging the gap between the two branches of the Carbon Cycle. By burning gasoline, coal, or natural gasses, which are products of carbon storage over millions of years, we quickly release this otherwise unavailable carbon into the biological/physical branch of the carbon cycle. Though the biological branch of the cycle has some storage capabilities, it is unable to process the extra CO2 flux from the geological cycle we are inputting through use of fossil fuels. It is explicitly for this reason that scientists are stating that we, as a species are increasing the concentration of atmospheric CO2 by our energy consuption practices.

So, coming back to riding a bike. When I ride my bike, I am using energy that has come from eating meats and veggies. All of these things are part of the biological/physical portion of the Carbon Cycle. Thus, any CO2 I contribute to the atmosphere was already part of the normal carbon flux due to photosynthesis/respiration. This is totally different than when I drive my car, cool my house, or use plastic grocery bags, where I am taking carbon that has been stored in the Earth’s crust for millions of years, and releasing it wholesale into the atmosphere. On this basis alone riding a bike is always better than driving a car. Period. Now, there are some important considerations to point out in Don’s favor here. My bike is made up of raw materials, including petroleum based products (ie, plastics, the grease I use for the chain, etc.), thus I do have a ‘carbon footprint’ which include some release of geologic carbon. However, compared to the amount of materials and CO2 used to produce a car, I am still doing better with the bike.

For completeness sake, I will lastly consider just how much more efficient my bike is verses my car.

I looked around a bit, but couldn’t find a stat for how much CO2 a bike puts out, but I did find out that typically an average human outputs about 1kg of CO2 per day. Hypothetically, let’s say I ride for 24 hours, and output 2kg of CO2. I averaged about 12 mph on my bike, so that would mean I would get 288 miles in 24 hours (I could only wish, but it will work for this example). Now my car, a 1997 Honda Accord produces ~8.0 tons of CO2 a year using the default mileage settings (45% highway, 55% city, 15,000 miles/yr) at fueleconomy.gov, which works out to 0.0219 tons/day, or approx. 22kg/day of CO2. Now, to be fair, it will not take all day to drive 288 miles. Assuming a speed of 55mph (as an average), it will take 5.24 hours to go 288 miles in my car, producing 4.8kg of CO2 for the trip plus the 0.22 kg of CO2 I breathed while driving. As a last attempt, I did the same calculation using a 2008 Toyota Prius rather than my faithful Accord. The Pruis would produce 2.45 kg of CO2 plus the 0.22kg from my breathing. This is still more CO2 contribution than for riding my bike, all using conservative figures meant to be in the car’s favor. Oh yeah, and this is all of course moot because I do not contribute to CO2 loading from breathing as discussed above.

So, it is beating a dead horse I know, but it is an important one. Riding a bike is significantly better for the environment than driving a car. End of story. If you hear otherwise, you are unfortunately being misled.

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7 responses to “Bicycles and CO2

  1. Okay, but what about all those cows producing methane?

  2. Mom, Those cows aren’t producing any more methane than the bison were before we killed them all off.

  3. Yesm, I knew that, but I can’t resist ribbing my boy a bit… and he knows it.. ha ha. Of course those bison were in the millions then, but they weren’t adding to a world full of auto emmisions and factory discourse either.. sad. 😦

  4. I didn’t mean for you to go to so much work over my statement about bikes v. autos. What I meant to say was that America is not set up for bikes. For most people, bikes are not practical. Our cities are too spread out, they are built on hills, the population is older. etc., etc.
    Let me give you an example; when we were in Germany we saw a lot of older people on bikes, and the area was a little hilly, but they only had to ride for three blocks at the most to get to the grocery store, or bakery. Every little neighborhood had a small grocery and bakery. We don’t have that. Also, they bought food on a daily basis, while we shop for at least a week at a time usually. Our neighborhood groceries were forced out by supermarkets. But don’t feel bad about that happening in America; it is happening there now also. Let’s not forget that Germany invented the freeway!! They call it the autobahn, and there is no speed limit. Talk about gas useage!! And they pay about $8 a gallon!! I didn’t see one old person on a bike last year. Although I was never to mainland China, I know that bikes were, and still are a big mode of transportation, but I also notice that they are now going to the auto, and that is why the price of gasoline is going up. China and India are now causing a demand on oil. Anyway, that is what I was trying to say about bikes v. autos. The next time yhou come to visit, I’ll let you ride a bike down for groceries, because I sure won’t do it. LOL For most of us, it just isn’t practical.

  5. I just had another thought about bikes v. autos. You work in an office/classroom atmosphere, and the only exercise you really get is on that bike going back and forth between home and the office. How far is it between your home and office?
    Now think of the poor guy who works hard physicly for 8 hours, and lives on the other side of town because he wants his kids to go to a good school? And if he wants to use mass trans will have to make three transfers to get home.
    I’m just trying to point out that for most people, riding a bike to work is not practical. If it is, than it would be nice if they would. If it isn’t, hey, we can’t all be lucky.

  6. Thanks for the comments! I didn’t write this to attack btw, I had been wanting to write something like it for a time, you just made it convenient πŸ˜‰

    You may be surprised, I’d ride down your mountain…maybe not up…but down πŸ™‚ You are right, it isn’t always practical, but it sure makes sense in many more situations than people give credit.

    Also, yes I do have a desk job some of the time, but lately I have been working as hard as anybody in the field (the last 2 1/2 months). More often than not (like today) I have ridden my bike to and from work despite the hard manual labor during the work itself…

  7. That’s good!! Setting an example is the best way to show others it can be done. By the way, there are more people riding up the mountain now. Of course they are teens, or in their 20’s at the oldest. They are the ones doing it for the exercise, or they are getting ready for the Seattle to Portland ride, or the Mt. St. Helens ride. The serious bikers like you.

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