Originally a comment by AJ Milne on Stop all that reckless breathing!
I got thinking a bit about the carbon footprint of cycling a while ago; I do cycle to work now and then (at 28K, kinda a long haul, and annoyingly, I can’t fit the time in right now, due to other parental duty things, but I probably will be again in a week or two)…
What I was generally hearing (with the billion hedges/estimates you need to build in in our annoyingly complicated economies–and see one high-level estimate here): it’s almost always better to cycle (and I drive a Prius, which is pretty low impact, as cars go). But depends a bit on what you’re eating. Some foods, if you count transportation and the way they’re raised/grown, are pretty high impact, so probably, counting all that, you can wind up making more CO2 that way, but it would be an unusual meal…
… and, generally that would be because someone drove or flew the food to you, which you then ate, and when cycling, then burnt it to CO2. That last burn really wasn’t the problem (and note that that carbon, specifically, was pulled out of the atmosphere to make the food, at some point; it’s carbon effectively in a cycle). It was the stuff involved in moving the food, which, sadly, yes, generally isn’t in a cycle; that’s the stuff we’re pumping it out of the ground and burning. And, yes, some foods are otherwise a lot more carbon-intensive even to raise, since little of the carbon involved winds up even on your plate.
Also kinda amusingly, I guess: with gas prices where they are around here these days, I figure the calories probably usually wound up costing me about as much as the gas would have. But, of course, there are also a lot of other benefits to cycling. And I’m pretty sure none of this builds in the carbon impact of the healthcare system housing me years longer, if I don’t get some cardio somewhere, at least.