First up in a bunch of links I've been meaning to post: The Guardian had an article about a UN report that looks at the world's potential population over the next 300 years. Obviously, the paper's sub editor's mind was elsewhere when he/she came up with the unrepresentative headline "Population boom set to stabilise at 9bn by 2300":
The report, issued by the UN's population division, gives warning that even slight variations - "as little as one-quarter of a child" - below or above this two-child norm could produce dramatic swings, resulting in world totals ranging from as little as 2.3 billion up to 36.4 billion.
If fertility levels remained unchanged at today's levels, the current world population of 6.4 billion would rise to 44 billion in 2100, 244 billion in 2150 and 1.34 trillion in 2300, the UN says.
Fascinating to see people looking this far ahead for a change, and a reminder of what drastic differences a tiny change can make. None of the newspaper/website articles I found linked to the actual report, but you can get the PDF here (or read Google's HTML version).
Population growth is tied to energy resources. The projected future shortages of fossil energy will cause a massive die off.
Food, transportation and medical care are all highly energy intensive. Lack of energy will limit all of the above.