There's a lot of discussion these days around the world's population reaching 7 billion. The chart below is from A tale of Three Islands, an excellent Economist article on the topic.
The UN is projecting the world's population will hit 10 billion in 2100. But a growing number of demographers are starting to think the world's population will peak around 9 billion and then start to decline.
If Africa's economy improves as many expect, it seems likely their fertility rate will drop just as it has done in other developing economies (India and Indonesia are good examples).
If this happens, the world's population will likely start to level off in the 2050-2060 time frame and potentially even decline from there.
Can the earth support 10 billion people? We think so. But we're also in the camp that says we won't find out because the population will peak around 9 billion - and do so without a Malthusian crisis.
Here at Small Business Labs we find demographics more interesting than most people do. The reason is demographic trends are often highly inter-related with other trends.