Friday, March 8, 2013

Riding a Bike Causes Climate Change


Thus saith state representative Ed Orcutt, who represents the Kalama area of Washington State and is the ranking Republican on the House Transportation Committee.  To quote:
...the act of riding a bike results in greater emissions of carbon dioxide from the rider.  Since CO2 is deemed to be a greenhouse gas and a pollutant, bicyclists are actually polluting when they ride.
Before you lose yourself in mirth, stop to think for a moment about where this idea comes from and how other versions of it might be more widespread than you think.  Behind Orcutt’s statement lies the notion that pollution is when a substance goes from one place, where it is relatively harmless, to another, where it causes damage.  So a farmer, for instance, applies nitrogen fertilizer which increases crop yields, but a lot of it gets washed into lakes and rivers and then into the ocean, where it helps create a dead zone.  Pollution is what we call this process of moving chemicals to places where they cause harm, and the farmer is guilty of it.  The same, says Orcutt, with bike riders and CO2.  The carbon doesn’t do any harm when it’s in your body, but it creates environmental havoc when you breathe it out.

The reason why Orcutt is wrong is that bike riders, and the rest of us, are essentially way stations in the carbon cycle that courses through all living things.  We eat plant and animal matter (carbon), incorporate it into our own tissue, and release it when we exhale, secrete or decay after our death.  The carbon goes round and round.

Now think of a logical corollary to the Orcutt bicycle hypothesis: the couch potato solution.  Maybe we could reduce the buildup of greenhouse gases by encouraging everyone to eat junk food, watch TV and put on as much weight as possible.  Think of all the carbon we could store that way!  It would be fixed in our fat rolls and no longer floating in the atmosphere where it alters the earth’s radiative heat balance.  The problem, alas, is the same as with the bike rider story: all that carbon is going to be released.  It is in our bodies only temporarily.  We can alter the global distribution of carbon only by the difference between the total body mass before and after fattening up—a one-time effect—and only to the extent that this increase in aggregate human tissue is permanent.

Note that this is analogous to the role of forestry.  Bulking up our forests removes carbon from the atmosphere in exactly the same way as fattening up ourselves.  Of course, more carbon can be stored in trees than in people: there are more of them than us, and they are way bigger.  Still, the logic is no different, and the problem is the same.  Addressing climate change through forestry is measured by the one-off increase in stored carbon, and it works only if this difference is permanent, for which we have no guarantees.  Future people may cut down the trees we grow today, or the trees may not survive in the future climate.  (Couch potatoes may not last too long either.)

The moral of this whole tale is that the carbon problem is not a pollution problem in the familiar sense, because there is massive ongoing carbon exchange throughout the biosphere.  Atmospheric carbon is incorporated into plant and animal tissue; plants and animals release the carbon into water, soils and air.  Released carbon finds its way back into the atmosphere.  You can’t build walls between the different elements of the system to keep carbon from moving around.

But there is a point of pollution all the same, which is when carbon that has been stored deep in the earth—where it doesn’t move around very much—is extracted and burned, so that it enlarges the carbon cycle in toto.  We are talking here about fossil fuels, of course.  Humans can tweak the carbon cycle at the margin, through activities like forestry, but the future of our climate depends almost entirely on how much fossil fuel we manage to leave in the ground.

So go ride your bike, and don’t feel guilty about it, even if it means you’ll lose some weight.

2 comments:

Bill said...

The virtue of exercise aside, the key, it seems to me, lies in the counterfactuals. Here is lamebrain's quote:

"If I am not mistaken, a cyclists [sic] has an increased heart rate and respiration. That means the act of riding a bike results in greater emissions of carbon dioxide from the rider."

By comparison with doing nothing except breathing.

The main comparison of interest is with the amount of CO2 emitted if the cyclist drove to where he is going. (Not to mention other pollutants in exhaust fumes.) The amount of combustion necessary, and thus the amount of CO2 produced, to move the cyclist plus a two ton car the same distance is much more than that required to move just the cyclist. So to keep CO2 pollution in check, we want to discourage driving and encourage cycling. Big duh!

What about the comparison with walking? It has been a while since I took physics, and I never took physiology, but, walk or ride, the energy required to move the cyclist or pedestrian should be about the same, heavy breathing or no. The bike weighs something, though, so walking should produce somewhat less CO2. :)

Sandwichman said...

It's probably not possible to calculate the difference between walking and cycling. On the one hand, cycling increases the work-efficiency of the human energy expended -- you can go further on a given quantity of breathing and calorie burning. But there are also equipment and infrastructure costs in the roads and bikes.

The differences between cars and bikes are orders of magnitude though.

It's fascinating that Peter takes the time and effort to respond substantively to Orcutt's blather but dismisses critiques of the "growth" paradigm with a facile "I've never seen..." remark. I'm sure Orcutt has "never seen a persuasive argument" that fossil fuel burning is the real greenhouse gas issue, not riding bicycles.