A simple global food system model

World population has more than doubled during the past 50 years and it possibly will keep increasing up to 7.56 billions by 2020, 8.18 billions by 2030 and 9 billion by 2050 (FAO 2003) as shown in Figure 1. Not only the total amount but also the structure of population changed. In 1950, only 30% of the global population were urban dwellers, while in the recent years, this percentage has exceeded 50%, and more than 95% of the net increase in the global population