To be fair, the calories in question are those that are expended walking to the store. They perhaps should have subtracted the calories expended driving the car (>0) to get the net calorie opportunity cost of walking.
There is no 'perhaps' about it. This 'study' is frightfully stupid and lame. The author Chris Goodall is an idiot, and the editor of The Times should be horsewhipped for publishing it.
Suppose it takes 5 minutes to drive 3 miles, and an hour to walk it. Goodall compares the CO2 added to the atmosphere by the 5-minute drive, to the energy expended by the 1-hour walk
if he replaces the calories by eating beef. I'm not going to argue with his particular figures, they don't seem out of line to me.
However the equation should include what the driver is doing for the other 55 minutes, so they are both on the same calorie-expenditure clock. Even if he is sitting on his ass picking his nose, he will expend close to 100 calories.
The main issue though is the
eating beef part. Meat requires much more fossil fuel to produce than veggies and grains. This site claims 145!! times as much for beef as potatoes.
http://bicycleuniverse.info/transpo/beef.html
If the walker eats a potato or two, or anything that isn't meat, the equation hugely favours the walker. This is crap science at its worst.