There is a viral meme in the blogosphere and mass media suggesting that a single dog has the same impact as an SUV.  We blogged about it here.  Well, this advice and comparison turns out to have been based on some really dodgy calculations and is officially debunked.  Hopefully nobody took our advice seriously.  (I smell lawsuit).

First, let’s look at that SUV.  The calculations behind the internet meme say that it’s driven about 6,200 miles per year (10,000 km).  And yet, according to the US Department of Energy, a real SUV in the US is driven an average of 13,700 miles annually.  Already, the internet meme is off by a factor of roughly 2.2.  … their mileage assumptions certainly skews the numbers in favor of SUVs, and against dogs.

And then there’s the total energy estimates.  The pet-pessimists estimate that an SUV (in their calculations, a 4.6 liter Toyota Land Cruiser driven about 6,200 miles) consumes 55.1 gigajoules of energy in both fuel and amortized manufacturing energy every year.  That, too, is low.  A Land Cruiser gets about 15.25 mpg in combined city/highway driving — meaning that if it’s driven 10,000 km, it consumes about 407 gallons of gas, or 53.6 gigajoules worth of energy.  …  Yet again, they’ve low-balled the impacts of the SUV in a way that makes dogs look worse by comparison.  (Here, I’m drawing from the data collection and calculations I did for our CO2-by-transportation-mode charts. And I’m looking only at energy, not at the additional climate and pollution impacts of emissions from tailpipes and smokestacks.)

So even before you start to look at dogs, the authors have underestimated the environmental impacts of SUVs by a factor of at least 3.  And that’s not including the indirect impacts of SUVs — the parking spaces we build for them; the roads and bridges they drive on; the impacts of insurance and licensing operations; etc., etc., ad nauseum.

Then there’s flip side:  the authors’ claims about the impact of feeding pets.  The anti-doggists estimate it takes .84 hectares — or about 2.1 acres of cropland — to meet a a pooch’s food needs for a year.  There are a little over 70 million dogs in the US (the Humane Society says 74.8 million, the veterinarians say 72.1 million, and the pet food industry says 66.3 million, for an average of 71.1 dogs).  So by the authors’ estimates it must take about 150 million acres of US farmland to feed our dogs.  In all, there are 440 million acres of cropland in the US — suggesting that the equivalent of one-third of all US cropland is devoted to producing dog food.

We use the equivalent of a third of all US cropland to feed dogs?  That’s barking mad!

To see why it’s wrong, you can look from the bottom up, at the foods that dogs eat.  Or you can look from the top down, at the aggregate sales of dog food vs. the entire agricultural economy.  I’ll do both.

First from the bottom up:  what, exactly, do dogs eat?  The anti-pet-ites seem do a good job of calculating dogs’ calorie requirements.  Canines wolf down a lot of food:  a mid-sized dog consumes roughly 30 calories per pound of body weight per day.  (Smaller dogs eat as many as 40 calories per pound of body weight, while larger dogs eat as few as 20 calories per pound.  Call it the yapping-to-napping spread.)  I couldn’t find the average weight of dogs in the US, but the median dog breed listed here has an adult weight of 47 pounds.  If that’s representative of US dogs, then the average dog will eat 1,410 calories today, give or take — which, as I read it, is roughly what the authors’ figures imply.

It always does seem to come back to facts and numbers.

My reactions when I first read about the original meme were: 1) Yeah, dogs have a negative impact (but so does lots of stuff, e.g., washing your clothes-although I hear Jez has sworn off this too), 2) but this seems really exaggerated, dog food is made from the scraps people wont eat after all, 3) this argument was surely dreamed up by a diabolical denier-I can’t think of a better formulated argument to turn people away from measures to reduce AGW.

As a rabid animal rights believer, I just don’t see the moral logic of arguing that humans have any more right to life than a dog or cat.  So if we are going to get this extreme about it, the answer isn’t eat your dog; it is eat yourself (or jump off a bridge).

As David Horton commented on the original post:

I’m searching for a phrase … oh yes, “lies, damned lies, and statistics”. This is reminiscent of the nonsense proposition that because solar panels are black we shouldn’t use them because they absorb and radiate energy and so warm the planet.

I also think we run the strong risk of telling people that nothing they do in daily life can continue. And this is the kind of misconception that denialists prey on (back to the stone age etc). Telling people to kill and eat their pets because they are a major contributor to global warming is going to at best invite (quite rightly) derision and at worst have people say “oh stuff it, I’m not going to do anything if that’s what they are going to try to make me do”.

But I really like the overall idea Jez mentions, of calculating your own footprint, so that you can make your own decisions about how to change your lifestyle.  I do this exercise with  my marine ecology class, and the big surprises are always how big an impact air travel has and the importance of how much and fast you drive, not just the average mph of your car.

Anyway, for full disclosure, we have two dogs, two cats, two horses and three kids.  These things just happen.  My wife is a vet, so stray pets seem to find their way into our home.  I like dogs and cats, but have been lobbying for years to cleanse our family of them.  In part because of their environmental impact.  But really because I want to free us up to travel more, internationally, which will really do wonders for the planet…