The population of the planet is constantly increasing, and this growth can have many effects on the environment and the economy of the world. For example, as the world population rises, the pressure mounts on the agricultural sector to feed the millions of extra mouths. In predicting the rise of the world population, scientists use a number of variables.

Fertility Rate

The factor which affects the growth of the population in the biggest way is the fertility rate. The fertility rate is typically measured by the number of children per one woman of child-bearing age. If the fertility rate is larger than 2, the rule of thumb is that the population should rise, as there are more children than their parents. On the other hand, if this ratio is below 2, the population of the region may be destined for a decline.

Mortality Rate

A key factor affecting the growth of the population is the death, or mortality, rate. Just as the birth of new people increases the population size, deaths decrease it. The factors that affect the mortality rate include the availability and affordability of quality health care and lifestyle habits – for example, whether they smoke or do physical exercises regularly.

Immigration and Emigration

Cross-border migration is the act of people moving from one country to another. It affects the population size of both the host and destination countries. Emigration is caused by a number of factors, such as fleeing war, finding education, seeking new jobs or joining family members. When a person emigrates from a country, its population shrinks. When someone moves to a country from another place, it is known as immigration. Whether or not a person is allowed to immigrate is controlled by the country that will host this person.

Government Restrictions

There are some people in the world, including politicians, who believe that some countries need to have a birth rate restriction -- in fact, China already has its widely-known one-child policy. Such a restriction would prevent couples from being able to have more than the restricted amount of children. The argument goes that this type of restriction would cause fewer resources to be used and prevent overpopulation.