Since the 19th century, people had had the concern about global population issue and the development of technology , enhanced health and longevity. It made the explosive rate of population tend to slow down. .
Amber Fisher and Sergio Martinez, two PhD students at Department of Earth and Environmental Science of University of Texas at San Antonio, have done a research on the analysis of the global population. They pointed out that high rate of population growth usually occurs in developing countries and poor countries. By contrast, in developed countries, the population growth rate is low. In 2005, more than 60% of the world population is in Asia and Africa. More specifically, based on the data in the study, in the period 2000-2005, the rate of population growth in Africa is 1.4% per year, while the rate of population growth in Europe only 0.2% per year. Moreover, some developed countries have negative ratio such as Denmark with -0.04% per year. The main cause of this situation is the wealth gap between the regions. In poor countries, the level of awareness of people about family planning and education is limited. In addition, the standard of life in these countries is relatively low. "Seven billion will clearly be a serious challenge," Ban Ki-moon, the eighth and current Secretary-General of the United Nations, have told Time magazine (Bryan Walsh et al). According to United Nation, in October 2011, the world's seven billionth person was born. As estimated, the total population of the world will reach more than 10 billion by the end of 21th century. Scientists research that the earth can withstand the pressure of how many people, 10 billion, 20 billion or 30 billion. .
Despite the increase in population tends to decrease, it also has many negative impacts on human and natural system. The population explosion leads to expansion of residential areas. The biodiversity is declining because of the disappearance of many species of animals and plants.
