[Ken Kifer's Bike Pages]
ARTICLE: How Much Do Bicycles Pollute?
The quite bogus claim has been made that bicycles actually pollute more than small efficient cars since the cyclist eats food which has to be shipped and then cooked.

Do bicycles pollute more than cars? Do cars' catalytic converters and more efficient engines make them less of a problem than the inefficient human body that runs off of food produced by wasteful agriculture? How many calories does it take for a car, a walker, and a cyclist to travel one mile? How much CO2 is produced by transportation and how much by farms? Do farms produce other products than foods? How has food production reduced its use of fossil fuels? How do the transportation costs for food compare with the transportation costs for people? Why do I believe the cooking costs for food are low? Should we count all 350 calories of energy for cycling? How does the production and distribution of food compare with the production and distribution of automobile fuel? How does the energy and carbon dioxide production of gasoline and rice compare? How do automobile and human efficiency vary? What is the CO2 production of cars and cyclists? What are other ways in which autos are far from clean?


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How Much Do Bicycles Pollute?

This seems like a silly question to me, but two people have actually made the claim that bicycles can pollute more than cars. The argument is that cars are more efficient now and have catalytic converters while the human body burns food very inefficiently and uses food which is produced by a wasteful agriculture, and that food must be shipped, refrigerated, and cooked before it can be used. In replying to this argument, I am considering CO2 alone, since there is more information about its production, and I can use calculation to determine some of the figures. Unfortunately, I don't have the resources to know exactly how much energy is used for every process, so it will be necessary to use logic in some cases rather than figures.

However, even guess work can get us into the ballpark, since the differences between the vehicles are so great.  The figure has been used on the web that a car uses 1,800 calories to travel one mile and a person uses 35 kCal when traveling on a bicycle (source: Marcia Lowe of the World Watch Instiute). This is a difference of over 50 times, so even if food production is wasteful, there's plenty of room for inefficiency.

And when we look at the issue of how much energy it takes to produce food, we find that the production of food is not the major producer of CO2 in the US.  Transportation is responsible for 31% of the CO2 produced in this country, and automobiles are responsible for two thirds of that.

Farms do contribute somewhat to CO2 production.  US farming is responsible for 5% of the greenhouse gases produced in this country (CO2, methane, and nitrous oxide). Of course, by farm, we are including all farm products, such as cloth, paint, plastics, beverages, ornamentals, tobacco, animal feed, ethanol for motor fuel, and other industrial raw materials, not just food.  Farm production can also help remove greenhouse gases, since growing plants absorb CO2.  By the way, the production of food now requires less fuel than a few decades ago due to the use of no-till farming which has spread from one farm to another. Previously, the ground between the rows was plowed every week or two to control weeds, now a cover crop is grown instead, a cover crop that is often a second cash crop.

It has also been suggested that large quantities of energy are used to move food from one place to another.  I don't know where I would find figures to solve this one.  However, a simple illustration can demonstrate that this is not a major energy concern compared with automobile driving.  An automobile has about one horsepower of power for every pound of person carried; a truck carries over 50 pounds per horsepower.  People travel back and forth over the same roads every day, but food makes a single if roundabout trip as it is transported from the field to the local grain elevators, stockyard, or other storage area, to the factory, to the warehouse, and finally to the consumer. To reduce transportation costs, most foods are pre-processed within a short distance of where they are grown. The fact that I can buy a pound of rice for less than 50¢ indicates that no enormous transportation fees went into its delivery, because that money must not only pay the fuel costs for transportation and production but must also pay the salaries of everyone involved and provide a profit for the farm, warehouse, trucking company, and supermarket.

Third, the storage and cooking of the food does not involve much energy  either, although I have no official figures.  However, a little math, can illustrate that it's not so much a problem.  To cook my dinner, I heat at most two liters of water to 100° Centigrade which cooks half a pound or 800 calories of rice plus about 200 calories of chicken plus some vegetables for flavoring (I eat most of my vegetable raw). When I made my first bicycle trip, I cooked a big meal every day and used a wasteful gas stove, and so I would use one pint of gasoline a week.  A pint of gas produces 4,125 calories of heat, enough to heat 41 liters (about the same size as a quart) from the freezing point to the boiling point, if nothing is wasted.  Since I only need about 14 liters to do my weekly cooking, that's more than enough fuel.

So, although I can't come up with any figures, they would be very small potatoes compared to the waste involved in driving an auto.  After all, we are comparing 35 calories per mile cycling to 1800 calories per mile motoring.  In addition, my additional food consumption because of cycling is only a small part of the total.  For example, if a cyclist rides 10 miles a day, he or she burns only 350 calories of energy, which is just 36 calories over the amount of daily exercise needed to keep the cyclist from gaining weight.  My 500 mile weeks during the summer probably do not cost anything near 17,500 additional calories except while I am building up. My body become efficient enough on a trip that after the first few weeks, I actually have to limit how much I eat to prevent gaining weight.

Besides, there are costs in producing gasoline as well.  Before fuel can be burned in a car, it has to be pumped out of the ground.  I know that these costs are not always cheap because I learned that some oil wells in Texas had to quit pumping when oil recently reached $14 a barrel; it costs $14 a barrel just to pump the oil out of the ground.  Then the oil has to be moved to a refinery, often halfway around the world.  There, it is cracked in the refinery, a process that is much like cooking food to make it more digestible, and which also takes energy.  Then it must be transported to a wholesaler and from there transported to the local gas station.  So, there are many energy costs there too.  It looks as if gasoline does use less energy to produce, since gasoline is cheaper per pound than rice, but we don't know what the labor costs are for the two products.

Let's suppose that a car and a bike are both going to be used to travel a thousand miles.  Most automobiles will burn between 20 and 100 gallons of gasoline in a thousand miles, depending on their size, age, and method of operation, and we will include a car that gets the fleet average for passenger vehicles, or 19.1 miles per gallon.  We can also assume that the cyclist will use a quart of gas to cook food in that distance, if it makes everything seem fairer.

Gasoline has a higher energy value than rice because it is a hydrocarbon while rice is a carbohydrate.  Hydrocarbons are composed entirely of hydrogen and carbon, while carbohydrates have carbon, hydrogen, and oxygen, in fact, always enough oxygen to balance the hydrogen to produce water, hence the name: hydrated carbon.  Gasoline has an energy value of 33,000 kCal per gallon, and it  produces 25 pounds of CO2 per gallon. To get the same amount of energy from rice (33,000 kCal) as is found in one gallon of gasoline, we need 20.6 pounds of rice which will produce 30 pounds of carbon dioxide.  Yes, burning carbohydrates actually produces more CO2 per calorie produced; however, the CO2 from food is recycled from the air and does not increase the total amount in the air, while the CO2 from  gasoline is new to the atmosphere, from fossil fuels, and does increase the level in our atmosphere.  But for the sake for this comparison, we'll ignore that distinction as well.

Now, some cars get less that 10 mpg, or over 3,300 calories per mile, and some get more than 50 mpg, or 660 calories per mile.  The fleet average would be 19.1 mpg, or 1,728 calories per mile.

We can also look at human efficiency again. Calories per mile for people is a bit of a fiction like miles per gallon for cars.  No two humans will burn the same number of calories to cover a mile due to different speeds, body sizes, and fitness. The 35 calories per mile figure is probably based on an inefficient cyclist traveling at a slow rate of speed. My own figures, based on output rather than on consumption, show 150 calories per hour at 10 miles an hour (15 calories per mile), 300 calories per hour at 15 mph (20 calories per mile), and 600 calories per hour at 20 mph (30 calories per mile). Generally, the faster cyclists will be producing more output and thus speed per calorie consumed, so -- lacking better figures -- I am going to use the 35 kCal per mile figure for all cyclists:

Carbon Dioxide Production of Cars and Bicycles on a 1,000 Mile Trip
Vehicle Mileage Fuel CO2
Gas guzzler 10 mpg 100 gal/gas 2,500 lbs.
Gas saver 50 mpg  20 gal/gas   500 lbs.
Average car 19.1 mpg  52 gal/gas 1,300 lbs.
Cyclist 35 kCal/mile  22 lb/rice     32 lbs.

Now, some final adjustments need to be made.  I didn't include the quart of gas for cooking the food into this. That quart would add 6.25 pounds of CO2 to the total.  We should also consider the fact that even a small car can carry four people (we will ignore the CO2 that they are breathing, which would be about 1/3 of the production of the cyclist each).  So, the final results with the most economical car are 125 pounds per person with the car and 38.4 pounds per person with the least efficient cyclist, which means that the car produces over three times as much CO2 per person.  However, put 13 people in that car without increasing the fuel consumption, and you've got a winner.  Or produce a single occupant vehicle that gets 650 miles per gallon.  Unfortunately, the fleet average is 19.1 miles per gallon with 1.4 people per car, or 929 pounds of CO2  per person for 1,000 miles, which is 24 times as much CO2 pollution per person per mile, all of which is unrecycled.

So, the argument that a bicycle pollutes more than a car is entirely without merit. I think an argument like this stems from a false understanding of automobile pollution. The automobile and oil companies want everyone to see automobile pollution as non-existant, and certainly, it is invisible. However, the addition of catalytic converters has not meant the end of pollution for several reasons: 1) the converters don't catch all kinds of pollution, 2) they don't work properly in all vehicles, 3) not all vehicles have them or are required to meet the same standards (SUV's, trucks, and vans have lower standards, and these vehicles are increasing), and 4) we are driving more than ever before. So, instead of eliminating the pollution problem, it's getting worse. About 60,000 people die each year from air pollution, and forests in the Smokey Mountains and elsewhere are stunted by it, and most of this pollution is still coming from automobiles. Even if we could eliminate 100% of the noxious chemicals produced by automobiles, we would still have pollution from gasoline before it goes into the vehicles, and we would still be facing a global warming disaster brought about by the overuse of fossil fuels.

The only sensible choice is to reduce our use of automobiles. There are several alternatives in addition to riding bicycles, such as, carpooling or using mass transit to get to work, using one family vehicle for everyone instead of a separate car for each individual, combining several errands together into one trip, and using nearby stores instead of traveling across town for everything. However, using bicycles for transportation reduces the pollution even more and also provides much-needed exercise.

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