Something that’s been bugging me about cars

For a long time I’ve felt a background annoyance at the stupid “for environmental reasons you should buy a high-efficiency used car rather than a new prius or other higher-efficiency car” meme. And debunkings like this one didn’t satisfy me:

Is it more energy-efficient to buy a used car than a brand-new hybrid? – By Brendan I. Koerner – Slate Magazine

the Prius will consume 3,710 gallons of gas. Each gallon contains approximately 124,000 BTUs of energy, so that translates into 460 million BTUs’ worth of burned fuel. Add in the production energy, and the new Prius is responsible for a grand total of 573 million BTUs over its lifetime (not including disposal costs).

A Corolla with an automatic transmission, by contrast, averages 30.5 mpg—more than eight miles per gallon better than the average car on America’s roads. Over the vehicle’s lifetime, that translates into 5,656 gallons of gas containing more than 701 million BTUs of energy. Since the Corolla we’re considering is used, we won’t add to that total by factoring in production energy.

I realized that it’s because both the initial “contrarian” claim and this refutation are completely divorced from market economics. Or in philosophical terms, they’re Ayn Randian rather than Kantian. (or in physics terms, they hew to Galileo rather than Boehm… oh, nevermind)

In the world where the original claim and its refutation make sense, there’s an essentially infinite supply of high-efficiency used cars, and new higher-efficiency cars never enter the used market. Because if either of those assumptions is false (and both of them are) let’s see what happens:

If you buy a high-efficiency used car, that means someone else can’t buy it. They’re either going to have to buy a lower-efficiency used car or a new car, or no car at all. if demand for cars is unchanged by your decision, either you’re (by proxy) responsible for the BTUs spent manufacturing a new vehicle or for the BTUs spent by someone driving the less-efficient car they bought because you snagged the one they wanted. (And it gets worse: each decision to buy a particular car displaces some other potential buyer, so ultimately in the used-cars-only scenario you’re responsible for all the energy wasted by some gaz-guzzling battlewagon with blown piston rings that would have been junked had you not pushed every buyer down one notch by purchased a high-mileage used car.) In the new-vehicle case, the most you save is the difference in manufacturing energy between your original desire and the car that your displaced buyer decides on. But since all the people buying lightweight, higher-efficiency new cars are now buying used cars for ecological reasons, you might cause the saving of manufacturing any manufacturing energy at all. You might just have triggered the purchase of a Lincoln Navigator.

But what if demand for cars does change as a result of your decision? Can you now bask in the warmth of your ecological soundness? Well, sure, but the argument now boils down to “save the environment by not buying a car, or, preferable, arranging for someone poorer whom you don’t know or care about to not buy a car.” Contributing to someone else not having transportation to work or school or grocery store is an easy way to reduce carbon emissions, but it doesn’t have quite the self-righteous contrarian gloss.

Now look down the road five or ten years. All the original high-efficiency cars in the used market are clapped out. There aren’t a lot of newer high-efficiency cars entering the market because the people who were going to buy for ecological reasons them bought used cars instead. So what we have on the used market is a bunch of lower-efficiency cars. And what we have on the new market is a bunch of ditto, because manufacturers try (yes, try) not to build cars people don’t want to buy. It’s called responding to market signals.

Net result? More energy spent manufacturing (because the new-car manufacturers will be responding to the market of people who don’t care about manufacturing energy costs) and more energy spent driving (because the new-car market ultimately determines what’s available for used-car buyers). And this would be true even if today’s higher-efficiency new car had a higher lifetime energy cost than today’s high-efficiency used car. Because it’s not always going to be today.


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