SilverBadge wrote:I went to a presentation recently about lowering car CO2 emissions - one of the early stats to show how difficult reductions would be was that cycling had a CO2 cost of 34g/km (walking was even higher) compared to a current car average of ~170. I e-mailed the speaker to challenge this, as my own calculations work out as below 10 - his explanation (the figure wasn't his) was that this included the carbon cost of producing and transporting the extra food required, assuming both that (1) for the average rider cycling isn't an activity burning off existing surplus calories and (2) that if one ate extra calories they would be of "typical" carbon cost rather than e.g substituting higher calorie foods for lower calorie ones. Also left out of the equation is the realisation that (3) if vehicle efficiency improves, so will the calculated carbon cost of cycling, and (4) if fuel taxes were higher, then less travel-intensive food production techniques would be favoured, again with a reduction in calculated CO2 cost for cycling. And of course (5) a fitter person moves more economically and thus with less CO2 cost for those many non-cycling hours of their life too.
I've seen something similar done, in reality you make lots of assumptions about what the cyclist eats. I seem to remember it was possible to show that a cyclist used more calories than the car, which is fundamentally ludicrous; you can't realistically compare the most efficient method of transport on the planet with dragging two tonnes of metal back and forth.
Wonder how much energy is required to produce 1kg of sugar? I reckon I do about 100 miles to the bag.