Birth rate is highest in poor countries, population growth is higher, iirc, in more advanced countries, due to immigration and the sudden increase in birth survival rates due to medicine.
Considering it's going to be decades before third world countries make any real kind of environmental impact, it is, surely, more important (at least from this particular point of view) to worry about the actual emmission creators than culling the environmental competition?
This just seems to be passing the buck, "We're creating tonnes of pollution, so quick, blame Africa!"