Not to worry -
Population expansion and the rapid growth of that population over the past 150 years has been dependent on one commodity - petroleum, and those commodities that are dependent on petroleum for their production. Few people realize that 95% of today's food production is dependent on petroleum - and not primarily for energy.
In the last decade Asia has begun converting from a manure based agriculture production system to a western model based on NPK fertilizers. NPK fertilizers are totally dependent on petroleum - directly or indirectly. NPK (Nitrogen, Phosphorus, Potassium) largest constituent Nitrogen is produced from natural gas (currently very abundant in the US - but not world wide). NPK's phosphorus and potassium have to be mined using petroleum based fuels and petroleum dependent chemicals in their ore processing. While Potassium is the seventh most abundant element on earth, Phosphorus comes from increasingly scace phosphates which are now considered a peak commodity - like petroleum (get it - one peak commodity is dependent on another peak commodity).
A decade ago the US was the largest NPK exporter in the world. According the 2011 USDA Fertilizer Import Summary - the US imported over half of its fertilizer components in 2011 and has begun to import phosphates from Morocco (15% in 2011). Interesting to note that in 2002 China essentially stopped all export of phosphates from their country to assure their own supply. Another note - biofuel production usage of NPK could be four times our food production use.
So, don't worry about our unlimited population growth - it will be comparatively suddenly limited by the decrease in our food production ability as fertilizers become more and more expensive. Higher food costs will produce chaos (we've already seen some this in recent years) and the growing chaos will cause a drastic reduction in population through war and disease. Have a nice day.
