I think the parent comment is referencing the huge economies of scale you get on shipping things in bulk with respect to CO2 emissions. If you have 1,000 legs of lamb in a shipping container, the per-leg CO2 cost is low in comparison to one leg of lamb in a car, even if the distances are very different. A heavy truck gets maybe 6mpg compared to your car getting 25, but if the truck is carrying 1000x more items, the truck would have to go ~250 times farther to break even.

I'm not sure how it breaks out for air cargo (probably not great), but ocean and rail are both more efficient than trucks.

The problem is that's only amortizing on side of the equation. If you were to pick up that leg of lamb and a dozen other things on the way home from work then the additional CO2 cost from the lamb itself is negligible.

It's like saying cars produce less emissions than bikes by including the manufacturing costs of the bike but not the car.

Sure, it also depends what kind of car you're driving, how much traffic there is, how far you are from the grocery store, etc. etc. The original parent point I was trying to clarify is that transportation impact on the environment for most food products is low on the list of things we should be worrying about.

> It also costs less in CO2 costs to ship that lamb from NZ to a supermarket than to truck it in from a local farm to your fancy organic farmer's market.

How does the lamb get from the port to the grocery store? Is the port not roughly equidistant from the point of sale as the local farm? How is the “fancy organic farmers market” less efficient to ship to in the last mile before the point of sale?

Well that all depends on the exact numbers, doesn't it? But someone going to the farmers market twice as often as they'd need to go to the supermarket (because that produce doesn't last as long, although that mostly because of less efficient processing methods in small farms) is already almost surely polluting more than the person going to the supermarket.

That's not even mentioning the savings that can be had from home delivery. Although I had a local organic pig farmer deliver meat at home just yesterday, so that's not an advantage exclusive to large players (provided he has enough customers to do multiple drops on one tour - I should've asked him, come to think of it).

Meat (aside from fresh fish) is rarely flown.

That’s not really the point. Unless you go grocery shopping at the (air)port something else brings the goods to your store.