premise: The worlds population is expected to increase to more than 10 billion by 2050. Having a child in the developed world has a greater environmental impact than having a child in the developing world. Likewise having a large family in the developed world has a far greater environmental impact than having a large family in the developing world. This is because a child born into the developed world is much more likely to go on to have a high carbon dioxide emission lifestyle given that they are more likely to take regular flights, drive cars, live in a large energy-hungry home and so on. This has led some campaigners to argue that families in the developed world should think far more seriously about the environmental consequences of having children and should elect or be encouraged to have fewer.
hypothesis: If it were the case that all of the worlds future population growth was projected to occur in the developing world and that the population of most developed countries would have fallen if it wasn't for immigration, then the case made for smaller families in the developed world would be weakened.