[microcolonel]

Don't need to bulldoze much of anything to do something though. The inefficiency of buildings is a tiny part of the problem, especially in temperate climates; more mixed use zoning, and the relaxing of single family dwelling zoning, will have a dramatic impact on excess travel.

Transport accounts for basically a third of U.S. energy use, though it has been hardly growing over the last few years, which is a good start.

The most efficient car, bus, or train, is the one that you didn't ride.

[KevinEldon]

I think we agree. I meant inefficiency in building density not energy use. I was thinking about row houses in San Francisco and brownstones in New York City. Old short and inefficient buildings could be torn down and replaced with tall, dense, efficient structures; but people who own row houses, or rent apartments with high rents, or like the way their neighborhood is now don't seem to want this kind of transformation.

[Udik]

And over what time period would you finally offset the excess co2 introduced in the environment by tearing down and rebuilding existing buildings? They're already medium-density buildings, with considerable historical and urbanistic value. Seems a crazy idea to me.