Friday Question Followup

On Friday I asked about relative environmental impact of buying a new, more efficient car versus driving the old one. I got some good comments and emails, so thought I’d respond to a few here.

• A couple of people commented that they didn’t believe the idea that a new car wouldn’t be built if someone opted not to buy one. In the case of single person, that may be true (although I’d disagree with that as well), but in the case of a more widespread change in behavior, its patently not true. If many people extended the life of their car by a year (i.e. waited a year longer than normal to buy a new one), it would have a huge impact on the auto industry and result in less cars being built.
• I wholeheartedly agree with the “drive less” comment. That’s more important than any purchase decision. How much you’re driving also factors into the answer to my question. If you only drive a few thousand miles a year, its very unlikely that a more efficient car is a net win. If you drive 50K miles per year, its much more likely that a more efficient car is a net win.
• I’m intrigued by the comment about the usable lifetime of the car. That hadn’t occurred to me at all, and it definitely should be a factor of some kind.
• One commenter questioned whether the energy to build a car was significant. Josh Simons sent me this website which includes this study, which says that it is. Now this may have been written by the Hummer Owners of America or it may be totally accurate, I don’t know. But its worth looking at how they calculate that an H3 has a lower total energy impact than a Prius (yes, you read that right - read the study).

A couple of reasons that this kind of intellectual experimentation is useful for me. First, its a good reminder that none of these seemingly simple questions is really as simple as they look. These energy issues are deep, and its good practice to understand where the subtleties are and get in the habit of looking beyond the initial answer. I’m getting better at thinking these through, but I’m still surprised by some of the points every time, like the comment about lifetime above. Seccond, we’re embarking on a similar study on the complete energy cycle of computers, so its interesting for me to look at another complex product. More to come on this over the next few quarters.