Well, my dog food calculations went awry, as Richard Reiss pointed out in the comments. I slipped a digit.
To recall, there have been recent allegations that having a dog does as much damage as driving a large SUV, on account of the carnivorous habits of the dog. Now there's some question as to how much of the damage due to meat should be attributed to the dog, but even given a proportionate impact by weight, I found at a rough cut that supporting the dog was the equivalent of driving the SUV no more than 5 miles per day. It turns out that my particular calculation was wrong by an order of magnitude, and that it has to be corrected, but it needs to be corrected AWAY from the calculations of Vale & Vale, in favor of the dog. Even fed a diet of sirloin, it appears that the dog's daily impact is on the order of driving about a half mile.
But this leaves me in a quandary. My prior result was in the same ballpark as Eshel & Martin's famous result that personal transportation and personal food consumption in the US are of comparable scale insofar as greenhouse gas impact is concerned. Counting the human as triple the dog, and the vehicle thus as driven 15 miles per day, seemed consistent with that estimate. But now I'm left at a loss, since the meat impact is now coming out as tiny.
And now here comes a Worldwatch white paper claiming that meat dominates transportation!
This level of confusion is ridiculous. How the hell are we supposed to cap and trade stuff that we have such a fuzzy grasp of?
Let's revisit the fuzziest numbers in my calculation. I erred by a factor of 10 in the power consumption of the vehicle going at 40 mph, which I took to be 10KW but was listed at 100KW. The first number seemed more plausible to me, but it;s easy to check. Let's suppose the vehicle is getting 20 mpg. Then it is consuming two gallons of gasoline per hour. Googling "energy per gallon of gasoline" is immediately successful, yielding US gallon = 115000 Btu = 121 MJ along with another handy energy conversion reference page. So I get 33,700 W, neatly splitting the difference between the small number I expected and the large number I should have used!
OK, now it's an extra factor of 3 in favor of the dog (compared with prior calculations). A dog eating ribeye steaks is worth about two miles of SUV travel daily; a human about six.
The per capita mileage in Martin & Eshel was 200 per week, supposedly compatable to human impact, so I have only a factor of five to make up. Still a bit awkward. (Update: And half of that comes back because most people aren't riding SUVs. As Marcus points out in the comments, some of that comes from my neglect of methane and nitrous oxide in the dietary impact. So maybe we are still in the irght ballpark.)
This past weekend I saw a presentation at the Texas Book Fair (at the State Capitol, an innovation for which I have Laura Bush to thank, of all people) on the subject of Texas barbecue as a repository of authentic rural Texas culture. I love Texas barbecue; not the famous places like the Salt Lick, but the still-authentic ones like Black's in Lockhart. It would be a real pity to have to sacrifice this oddly satisfying and evocative bit of authenticity to sustainability. It's just not the same with barbecuing a chicken. Never mind a tofu.
To be sure, there are real ethical issues with even the smallest bit of meat. I don't deny that for a moment. But the environmental ones are new, and they need to be properly calibrated. I'm afraid the numbers are all over the map.
I'm totally unconvinced that the impact of a dog compares to that of an SUV, even lightly driven. My latest calculation moves things a factor of three in further favor of the dog, although to be sure the dog cannot carry as much cargo. But I'd really like to pin down just how guilty I should feel when I bite into a Texas brisket sandwich. Are these pleasures of the blessed or pleasures of the damned? The estimates have way too much variance. This question has a real answer, maybe not within a factor of two, but surely within a factor of fifty!
Let's get quantitative. How many miles in an SUV is a piece of brisket worth? Surely I should feel more guilty that I drove my Prius the thirty miles to Lockhart than that I stopped there for supper?
Oh, yeah, I parked the Prius around the block.
You cain't really pull into Black's in a Prius. It's hoard to expline. Sort of a Tixes thang.
Update 12/31/09: Similar calculations here.