Two extra Earths

Sometime ago I came across an analysis that stated that it would require two extra earths to provide the resources for all the world to consume at the North American/European/Japanese level. This has become my favorite example for enlightening people around me at why people would want to protest things like free trade. The thing is I don't remember where I saw this, and being the responsible pretensious scholar that I am, I want to be able to source the quote. Can anyone help me track this down? I seem to recall reading this on the WSN list but I am not sure.