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Dear Pablo: A website puts forth the proposition that riding a bike actually produces more carbon dioxide than driving a car because you are working hard riding a bike but essentially resting when driving. Can you look at their numbers?Wackos Grasping At Straws
In their attempts to make a case against the science of climate change, the far-right has seized on the argument that "humans are CO2 factories." In some cases this fact is used to portray those in favor of emission reductions as somehow anti-breathing. In this case though, the article's author, Ronnie Schreiber, is trying to make environmentalists on bikes into hypocrites while seemingly justifying the continued use of the single-occupant SUV. This is, of course, just the ammunition that the far-right is looking for.
The Argument Against Bikes
Schreiber claims that a cyclist exhales more CO2 while riding than a driver, who is essentially at rest. The author then compares the emissions from the cyclist's breathing to the annual emissions from a vehicle's fuel use. One of his conclusions is that "there are already four cars on the market that have lower CO2 emissions when carrying a single passenger."
The Argument Against The Argument
The assumption that a bicycle commuter will have a VO2 measure (the volume of oxygen you can get into your blood) that is 10 times higher than their resting VO2 (3 ml/kg/min) goes against the experiences of all the fellow cyclists that I talked to. One told me "I exercise at 2/3 of my maximum heart rate and know what that feels like. When I cycle for basic transportation I do not work harder than walking and am nowhere near the hard breathing of exercise."
The next assumption that I take issue with is the use of 15,000 miles per year for both the car and the cyclist. If a cyclist rides 15,000 miles to work over the course of a year this equals 58 miles per day. It is needless to say but this type of dedication is rare and most bike commuters travel only a few miles, or combine their trip with public transportation. And while they are sitting on the bus or train they are producing no more CO2 than their SUV-driving counterpart.
Finally, and most importantly, the exhalations of humans and animals are biogenic, meaning that they are essentially "carbon neutral" (unlike the emissions from burning gasoline). Since most of our caloric intake comes directly, or indirectly, from plants, and since those plants grow by converting atmospheric CO2 into oxygen, most of the CO2 that we exhale originally came from the atmosphere. I write "most" because there is some portion of caloric energy that can be attributed to synthetic fertilizers and the production of some foods results in emissions of methane (CH4) and nitrous oxide (N2O), which are both much more potent greenhouse gasses than carbon dioxide is (21 and 310 times as potent, respectively).
So Where Does That Leave Us?
So, clearly the conclusion that cycling creates more emissions than driving is based on false assumptions and those emissions are mostly biogenic anyway. A better argument can be made that, if all of your caloric intake comes from corn-fed factory-farmed beef, your net impact on the climate is worse than if you were to eat a vegan diet and drive. This was the conclusion of the very first Ask Pablo article back in September of 2006.
Pablo Päster is a weekly columnist for TreeHugger.com, an experienced greenhouse gas engineer and the Senior Environmental Program Manager at Hara Software. Send your questions to Pablo(at)TreeHugger.com or submit the via this form and connect to his RSS feed.
More Resource On Riding Your Bike:
Outraged Cyclists Re-Paint Removed Bike Lane, Guerilla Style (Video)
Woot! Bike There Feature Added to Google Maps! (Video)
The $350 Electric Commuter Bike