"People should make the effort to do their bit" said my wife. We were discussing Global Warming, and how The Sky Is Falling In, etc. This got me thinking. How I know what that means? I bet that most of the received wisdom is wrong. I thought I'd do a bit of research and look at the bicycle. I'm a keen cyclist (I've even been on a 2500km 3 month tour of New Zealand on my Airnimal folding bike). Cycling must be the answer, right? Hmmnn..
A typical car does about 35mpg, or 6.7 litres/100km. At 0.032 gigajoules/litre for gasoline, that works out at 2150 kJ/km.
Cycling burns about 20 calories per kilometer. Obviously a fat person on a 20kg mountain bike burns a lot more. But we can't just use the 20 calorie figure straight: those 20 calories come from food, which has to be grown, harvested, processed, transported, stored and cooked. Which takes energy. Lots of the energy is in transport, and a lot is in the fertilizer (which is made from natural gas). On average, it takes 7 calories of fossil fuel energy to make 1 calorie of food energy. That's an average. It's much worse than average if the food comes from an animal that has to be fed itself (as much as 70:1). And it's horrific if the animal is itself fed on meat (e.g. tiger penis soup). But let's go with the 7:1 average. That puts cycling at 586 kJ/km. That works out at a gasoline equivalent of 107mpg. Good, but not that great. Not compared to a scooter (80-100mpg), or a diesel train per passenger (182mpg). Even an airline seat isn't that bad (66mpg long-haul and 40mpg short-haul).
What this really means is: the situation is complex. The Devil is in the detail (no doubt there are points against my calculations). A blanket "flying is bad", "cycling is good" response is just not right. Which is why the Stern Report recommended a levy on CO2-equivalent emissions, with a trading scheme, and let the market work it out for itself. That means if A is cheaper than B it'll probably be better at slowing climate change, too. Then we just have to do what we've all got a lot of practice and skill at: choosing things based on their price. Simple, eh?
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3 comments:
So you calculate every last gram of CO2 used by the Cyclist, but forget all the extra CO2 used by the car in refining the fuel, transporting the fuel and even the manufacture of the car itself (and delivery to showroom) compared with manufacturing a bike!
The well-to-pump losses are less than 20%.
The other costs are capital costs, which is not something we're interested in (the question is "should I use the car or cycle?" not "should I buy a car or a bike?").
Still, the lifecycle costs are interesting: a Prius emits more than a Chelsea tractor, and we do want to answer the question "What car should I buy to reduce my carbon footprint?". But I'm sure the politicians know best in favouring the Prius with tax breaks, eh?
Having just bought a carbon framed bike - I DREAD to think what my carbon footprint will be now..
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