Raj Patel

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?

8 comments on “Raj Patel

  1. For long distances, (more than a couple of miles?) driving is clearly less CO2 intensive than walking, and for very long distances, flying is less CO2 intensive than driving, obviously. But this is chicken-and-egg. If everybody walked to the shops, then we’d build more houses near the shops, so distance travelled would come down etc.

  2. “For long distances, (more than a couple of miles?) driving is clearly less CO2 intensive than walking”

    Cite?

    Anyway @ Tim – the point is that when you reach the level of obesity (BMI of 29), the calories required to maintain your base metabolic rate (i.e. to get through the day without taking any exercise at all) are /higher/ than the calories required by someone of normal BMI to not only get through the day but also take enough exercise to stay that way.

  3. “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.”

    Surely if one’s calculating a carbon footprint or whatever for the drive to the shop, then one has to include the energy used/emissions emitted in the refining and transport process to get the petrol to the pump?

  4. Are they using the best BMI as advocated by Puritans, or the substantially larger best BMI as inferred from mortality data?

  5. They did the calcs in a Telegraph op piece a while back. Driving does produce less CO2 than the respiration required for walking but…and here’s the point the author missed…driving releases carbon into the atmosphere that was previously tied up underground as oil, walking releases carbon into the atmosphere that was previously tied up as plants and animals. One is a net gain to the amount of carbon in the carbon cycle, one is neutral. Thus it is only the first that need concern us…or neither, as is your belief.

  6. Dr Cllr P Thomas is confusing the two halves of the equation.

    One is the ‘output’ side (I assume that climate is indifferent between CO2 derived from food or from fossil fuels) and t’other is the ‘input’ side (whether those emissions are derived from plants and animals consumed in the past few hours, or whether those emissions are derived from plants and animals that died millions of years ago).

  7. Ah, but when did you last drink petrol and walk, or put food in your car’s tank? What mode you choose to travel determines the input as much as the output.

    The biofuels debate is one of inputs, the car vs. planes is one of output. The answers in both cases can be surprising.

Leave a Reply

Name and email are required. Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.