If you want to do a quick estimate on if we're over populated, a quick bit of maths will sort you out, and I did this recently.
Supposedly it takes 0.5 hectares of land to feed a single person for a whole year (cit. Google). The UK has 241,930 sq km of land, of which 71% is agricultural and a population of 64,430,428 (figures from CIA World Factbook).
If you bang these through a few equations you find that the UK can only physically feed 34,354,060, so about 46% of the current UK population would starve if International trade shut down.
If you apply the same formulas to the US or Canada, the US is capable of feeding about 800,million people, and Canada at about 120 million.
My maths don't take into account idle arrable land not currently being farmed, or the fishing industry.
These aren't perfect calculations. It's just a rough calculation done on a whim... I began applying the calculations to a number of countries and found some had healthy populations and others were dangerously overpopulated. I got bored after 30 mins of copy & pasting figures though, and I wasn't able to find good reliable sources of data.
Biting the hand that feeds IT
