Not sure that I follow/agree with the logic...
A country's (or a particular lifestyle's) carbon footprint is calculated by multiplying its per-capita carbon footprint by the number in that particular population. That much they have understood.
But what they are saying is that because the Developing World has a smaller per capita carbon footprint, it is far less important that the Developing World makes the effort to control population growth. This logic only works if you assume that:-
1) The Developing World has no right to improve its lot and to aspire to a Western lifestyle, and therefore there should be a halt in all attempts to improve the plight of the desperately poor. Any improvement in their conditions (barring some as yet unknown leap forward in technology) will dramatically increase their per capita carbon footprint. Can't have that. Sorry, mate. You're poor. Better get used to it.
2) A complete halt to all migration from the Developing World to high carbon footprint countries. And, by implication, a halt in migration from countries with net population growth to those without. We've had to cut down on our babies, why haven't you?
Funnily enough, I didn't notice that being called for. Probably because they wouldn't have looked nearly as trendy.
Global warming may be a problem, but if a way was found tomorrow to suck the excess carbon dioxide out of the atmosphere, the planet would still be in trouble. As engineers we can all try to improve things on the per-capita front, but the most important message just doesn't seem to register.
IT'S THE OVER-POPULATION, STUPID.