Dave is a critical consumer of information and notes that there is little given in this particular article (which appears in the “Media & Advertising” section) as far as numbers. As I’m not an agronomist, I don’t have all the relevant numbers at my finger tips, but I’m happy to set up some equations into which reliable numbers can be plugged once they are located.
First, there’s some unclarity in the sentence quoted above as far as what exactly is being compared when we’re weighing the relative importance of choices about driving and choices about eating. Is it a comparison of greenhouse gas (GHG) emissions? Petroleum consumption? The whole bundle of factors that have an effect on global warming?
Also, as Dave pointed out to me, which SUV and which Camry are we talking about? What animal sources of protein and what plant sources of protein? There are lots of specific details that could make a difference.
Your driving decision’s impact seems like it could be calculated as:
((Average miles/day)/(Average miles/gallon)) x (kg GHG emitted/gallon of gas consumed)
Of course, if you’re just tracking how much gas you’re burning, don’t multiply by the last term.
I don’t know whether there’s a uniform rate of GHG emitted per gallon of gas a car consumes — either for a single vehicle or vehicle type or across many vehicle types. In the absence of expert opinion on this, I’d probably assume it’s a constant. (If you have an expert opinion on this, please chime in!)
I drive neither an SUV nor a Camry. A pretty fuel efficient SUV gets maybe 20 miles per gallon. A Camry is probably not too far from a Corolla in average fuel efficiency, so we could estimate that at around 30 miles per gallon. For someone with a daily commute about the same distance as mine (a 50 mile round-trip), this hypothetical commuter would burn 2.5 gallons of gas with the SUV and 1.7 gallons of gas with the Camry. However much crud is being emitted from the burning of the gas (assuming a constant rate of crud per gallon of gas consumed), the SUV commute puts out 47% more of it than the Camry commute.
That was the easy calculation. Now for the food.
To simplify, I’m going to deal with only one macronutrient, protein, since that’s the one people seem to be most interested in getting from their meat. (The fat is like the prize at the bottom of the cereal box.) If we’re sticking to GHG as the thing we’re comparing, we’ll be looking at:
(kg protein consumed/day) x ((GHG emissions/kg to produce the protein source) + (GHG emissions/kg to transport the protein sources))
The USDA says that my daily protein intake should be around 80 g (or 0.080 kg), but it doesn’t tell me what particular source of protein to favor, or how to apportion those 80 g among different potential sources. And depending on the source, the balance sheet may come out quite differently.
For example, the GHG emissions involved in producing 1 kg of beef, pork, chicken, or (farmed) fish may all include GHG emissions related to shipping corn to feedlots. However, cows, pigs, chickens, and fish have different rates of conversion of grain input to flesh on their bones. Also, ruminant animals like cows also put out their own GHG emissions via farting; chickens don’t fart as much.
Note that you can’t even easily pin down GHG emissions in the production of 1 kg of a particular kind of meat. Corn fed beef will have GHG emissions from transport of the corn to the feedlot, while grass fed beef will presumably be grazing on the grass where they are, eliminating some of the GHG emissions. (Do they ship grass — or truck cattle that are fed grass considerable distances to the grass?)
For a plant source of protein, there’s less farting (by the plants, anyway), but there are still GHG emissions associated with shipping. In addition, to the extent that your plant based protein might be processed (like tofu), it’s quite conceivable that some part of the processing might involve GHG emissions.
Really, without specifics about what you’re eating, how it was fed or produced, and how much fuel was consumed getting it to you, it’s impossible to hold up a kilogram of protein from one source and a kilogram of protein from another and say anything very sensible about which contributes more to global warming. Locally grown whole soybeans probably contribute less GHG emissions than beef from gassy cows fed corn trucked in from 1000 miles away, and then itself put on a truck for hundreds of miles to get to the store. But it’s not obvious that soybeans that are shipped 1000 miles to make tofu and then shipped hundreds of miles to get to the store would lead to lower GHG emissions than an equivalent amount of beef protein from locally raised grass fed cows.
Of course, there are other inputs to meat and plant based proteins that are environmentally relevant — like how much water is required to produce 1 kg of protein of each sort. But if this is included, how can we ignore the other environmentally relevant inputs (and outputs) involved in the production of the Camry and the SUV? In a fair fight between changing what you drive and changing what you eat, you’d have to take this all into account.
None of this is to say that we shouldn’t bother thinking about how our choices impact our climate or environment. To me, the take-home message is really how alienated we are from where things come from, what’s involved in making them and getting them to us, and what the hidden tolls might be from the choices we make on autopilot.
Milton Friedman said the only thing we need to know about a product is its price. Maybe that’s true if we’re just interested in buying and selling stuff. But, seeing as how we live here on the planet we’re using to make and move around the products, we might be better served by the reminder (from a character in the movie Shallow Grave) that knowing how much money you paid for a product is not the same as knowing what it cost you.
Even if the complicated path our protein sources (and cars) take to come into being make straight comparisons hard, it probably wouldn’t hurt us to notice some of the costs that are incurred before we make our purchase.