It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Friday, October 30, 2009

Dogs, SUV's, and Freaks

Ray's excellent takedown of Freakonomics in RealClimate has me shaking my head about people's abilities to discuss even the arithmetic, never mind the algebra or calculus or statistics, of global sustainability issues.

Of course, Ray is exactly right, not just in the substance, but in the fact that the substantial argument in question is elementary.

Now I am going to say something harsh, but I'm afraid it needs saying.

Anybody who writes on this stuff ought to be able to figure as much out on why the solar panel/albedo question is moot in a few minutes. I mean ANYBODY, not just economists, who writes on this stuff. To be clear that includes journalists. If you lack the skills to do the arithmetic, in my opinion you should not actually be writing on sustainability issues. Period. Also, if you missed the fact that any albedo effect is swamped by the greenhouse effect, if the question didn't instantly jump out at you on reading the claim, you should be asking yourself very seriously whether your grasp of climate change is sufficient to write about it.

The same holds for many other "consider a spherical cow" type questions. If you can't do math with large numbers you should find another beat. What you are doing is the opposite of helping. (That said, what am I to make of Joe Romm's "they are not black, they are blue!" response to the panel albedo issue?)

While I was pondering these matters, a tweet arrived from @Revkin way:
Your dog a bigger CO2 source than an SUV? http://j.mp/PetCarbon (Finally had chance to read; math seems to hold up?)


Well, at least there's that question mark, but as you can see, it generated a lot of retweets.



Best to nip this one in the bud. I found a very handy page for back-of-envelope energy calculations. Please let me know if you find errors on it, because I plan to refer to it a lot in future.

So, it claims that the energy of a human is about 100 watts (seems about right) and of a car going a sustained 40 mph is about 10000 watts (also seems believable; it's about 13.4 HP). So let's figure a dog is about a third of a human, consuming about 1/300 of the car. Roughly speaking, then, the energy of a dog day is equivalent to the energy of driving a car for about 5 minutes, or a big SUV for about two and a half.

So at first glance it appears that there's really no contest. Even though the referenced article presumed only 10,000 km per year (6300 miles) that's still about 20 miles per day which is a long way to drive in 2 and a half minutes, especially at 40 mph.

For this to come out in favor of the SUV, we need to get up to a half hour, (even leaving aside the manufacturing and ancillary costs which the original article claims). To do this, we have to make a very unfavorable comparison between food energy and petroleum energy, a factor of about 8.

Now, there are claims that the food we eat consumes about 400 gallons of gasoline per year. This is a few bucks a day, and sounds plausible to me. So about a gallon a day, or a third of a gallon for the dog, if the dog's consumption is equivalent. Which will get your SUV about 4 miles further. Still not enough to get the 20 miles though.

Then there's the fact that most of the meat your dog eats is by-product of meat production for humans, rather than independently produced. I'd argue that proportion is free, which greatly reduces the impact of the dog.

However, consider the cost of a meat-eating full grown adolescent child. You will find the child's food supply (or yours) is indeed comparable to the cost of a lightly driven SUV.

5 comments:

Hank Roberts said...

> by-product of meat production

It's not just free; it's material they'd otherwise have to pay money to dispose of properly at a rendering plant.

Richard Reiss said...

"..So, it claims that the energy of a human is about 100 watts (seems about right) and of a car going a sustained 40 mph is about 10000 watts (also seems believable; it's about 13.4 HP)."

I think on the chart, the claim for a car is 10 to the 5th, or 100,000 watts
(which would be 134 hp, by your conversion of watts to hp)

http://physics.syr.edu/courses/modules/ENERGY/ENERGY_POLICY/tables.html

Brian said...

I agree with Hank, but even more than that, creating value for meat byproducts increases the demand for animal production. A cow can fetch a higher price because you can sell the byproducts, so you get more cattle production.

ourchangingclimate said...

"Then there's the fact that most of the meat your dog eats is by-product of meat production for humans, rather than independently produced. I'd argue that proportion is free, which greatly reduces the impact of the dog."

I believe that in LCA, it's customary to assign impact to 'users' relative to their economic use of the product. I.e. if part of the meat is sold as pet food, it gets part of the impact assigned to it as well.

Likewise with train travel: If I hop on a train, net emissions do not go up (apart from an insignificant increase in weightbeing transported). But in an LCA type analysis, my traveling is reponsible for part of the train's emissions.

It has perhaps more to do with accounting than with reality though.

Bart

King of the Road said...

To Richard,

The table referenced does, in fact, show 10^5 watts for a car at 40 m.p.h. but this is not correct. Let's think about it for a minute:

10^5 watts is 10^5 joules/second. I'll assume about 20% overall efficiency for fuel conversion so that 5*10^5 joules of thermal energy per second would be coming from the burning of gasoline.

A gallon of gasoline, as Michael correctly points out in a later post, will release about 120*10^6 joules upon oxidation, so a gallon would be used every 240 seconds, or 15 gallons per hour. 15 gallons to go 40 miles is 2.7 miles per gallon. Clearly this is incorrect.