It occurs to me that the level of American consumption has always been unsustainable in the long term given the contemporary technology at any given time. New York city was on the verge of uninhabitable because of all of the horses and their needs before Mr. Ford got his groove on.

The best that can be said is that the level of American consumption is unsustainable given the current level of technological development. What I think has made America such a singularity on the world stage is that the Americans have been able to use innovation to stay just a tiny bit ahead of "unsustainability" and do so with remarkable consistency.