Sorry, but how does this work?
They observe that "petrol tanks and stomachs were competing well before biofuels were proposed to tackle climate change," since transportation and industrial agriculture are both premised on cheap fossil fuel. One way to tackle the competition for a scarce resource is to change transport policy – a shift towards walking and cycling would reduce both the demand for fossil fuel, and secondarily mean that there were fewer overweight people, thus driving down the need for food. All well and good.
They estimate that a population of a billion people at a healthy body mass index would use a total of 10.5 MJ through the daily business of eating and living.
And then they throw in this grenade. It\’s worth quoting at length to see the damage that gets done subsequently.
"An obese population of 1 billion people with a stable mean BMI of 29.0 kg/m2 would require an average 7 MJ of food energy per person per day to maintain basal metabolic rate, and 5.4 MJ per person per day for activities of daily living (calculations available from the authors). Compared with the normal weight population, the obese population consumes 18% more food energy."
It\’s a straightforward comparison between a billion not-quite-overweight people and a billion obese people.
If those obese people become not-obese by exercising more then their food consumptions doesn\’t go down. Indeed, dependent upon how much exercise they do, their weight could come down while their food consumption goes up.
If they got slimmer not by exercise, but by eating less while using more fossil fuels for transport (instead of walking and cycling) then food demand might go down.
In fact, there\’s been one researcher who claims that using your car to go to the shop is "more efficient" than walking, as the calories you need for the walk take more emissions to create than the petrol gives off.
So I\’m a little confused here. My understanding is that farming plus the inefficiencies of human conversion of food into energy mean that exercising, that walking and cycling, will increase food demand, not reduce it. If that\’s correct, then what are these people talking about?