On the 30th of October, 2011 the world population reached 7 billion. This means a net increment of 1 billion over the past ten years. Based on this trend, the U.N. Population Fund predicts that, at the end of this century, world population will reach 10 or even 15 billion. This is a linear thinking that one deduces the future performance of a system from its past performance. The curves of population are full of non-linear changes in history. For example, for about one thousand years, from the Han-dynasty to the Song-dynasty, the population of China has been oscillating between 55 million and 15 million. When the country was united and society stabilized, population increased to 55 million, but when there was internal warring, famine and infectious disease, it reduced to 15 million.
In the 20th century, as the globalization of industry civilization continues, world population has been increasing, but on the other hand environment pollution, the greenhouse effect and resource shortness also continue; and if these negative factors are not kept in check, they will create wars for resources, natural calamities and famines. As a result the global population would be reduced to 5 or 6 billion.
