He who refuses to do arithmetic is doomed to talk nonsense.Recently I have heard, both from a genuine climate denialist (the only one I have met in person, she was charming and infuriating) and from left wing bloggers that the negative manufacturing impact of a Prius outweighs its environmental positives.
Here's a peculiar video (it meanders back and forth into and out of sarcasm in a way that I find exasperating) wherein numbers are bandied about to intimidate, but no serious comparisons are made. Nevertheless, Jerry Mander, who among leftwing kvetches is one whom I admire more than most, is in there arguing against buying Priuses. He suggests that buying a used car has a smaller impact.
Before starting to think about this, that if you are more worried about peak oil than about climate change, let's stipulate that the Prius is a clear winner. If we switch to lower fuel consumption vehicles, the liquid fuel will last longer and the transition to alternatives will be smoother.
What about climate change? My initial response was that Mander's position is ridiculous. I decided to do a back of the envelope calculation to prove it, and I failed.
I did my calculation in dollars. Suppose I fill the tank of my Prius a thousand times over its lifetime (a reasonable number.) Suppose, generously, that an alternative car would have had half the mileage. So we have saved twenty or thirty thousand dollars worth of gasoline on a twenty-five thousand dollar car. Case proved, right? There is no way thirty thosand dollars worth of energy went into the manufacture of a twenty-five thousand dollar car.
But wait. Manufacturing typically uses coal, not petroleum. Petroleum has not been competitive with coal in stationary manufacturing for a long time, as liquid fuel is much more in demand for portable engines. Also, there are huge distribution costs and consumer taxes associated with gasoline that don't apply to coal. So let's backtrack to the historical pump cost of gasoline before the shortage started to bite, about a dollar a gallon, and assume only half of that is energy cost, the rest being tax and distribution. Now we have cut the actual energy savings to the equivalent of $5000 worth of fuel. Can the energy component of manufacture and delivery of a Prius exceed $5000? Hmmm, that starts looking plausible.
OK, but we aren't talking costs, we are talking impacts. Of course most stationary large scale manufacture is coal-fired, and coal has roughly double the climate impact of petroleum. This means the break-even point on climate change is on the order of $2500 worth of coal.
All very crude estimates, but a bit shocking.
So I not only failed miserably to prove that the Prius is a net gain on the climate front, I find in the end that the contrary is quite plausible. I haven't proven Mander's position, but it seems well within the range of possibility.
However, I missed a point that goes the other way. We are talking about the *saved* fuel so we should be talking about the *excess* manufacturing energy. Does it take that much more energy to manufacture a Prius than a comparable non-hybrid? That's the number we should really be thinking about.
I imagine the bulk of the extra energy cost if there is some is in the manufacture of the battery. Replacing the battery costs, what do you know, about $3000. Hmmm.
As the video points out, there is also a direct environmental cost in terms of the mining and refining that goes into the battery, but I would think this would be tiny in comparison to global climate change, no matter
So the back of the envelope analysis is inconclusive, but so far leans in favor of the Prius as a net positive in climate change, compared to a conventional vehicle, although much less obviously so than you might suspect.
The people claiming that it is a net negative really ought to come up with better numbers than these and make a quantitative case, though.
Remarkably, great minds thinking alike, Climate Progress has something to say about this peculiar meme; Joe apparently worked harder at this one than I did.
Of course, whatever we choose to drive or fly, we should drive or fly less.
Does it make environmental impact sense, as Mander argues, to preserve nasty old equipment in rather than purchasing less nasty new equipment which has manufacture costs. I guess the answer is, that depends on the new equipment and the old equipment as well as how you cost things out. You'll have to do your own arithmetic, and the information you want won't be all that easy to find.
But hey, I bought my Prius used. :-)
So I am off the hook, right?
Update 7/29/09: This silliness is still hanging around, as silliness does. There now is a more substantive response on The Energy Collective.