It is obvious that the recent trends, described in the previous section, have consequences on the future population growth. So, the demographic dynamics has a great inertia: a part from certain specific phenomena that could suddenly change the population volume, such as natural disasters, massive migrations, etc., the demographic evolution of a country or region is relatively slow and constant, thus, foreseeable.

Generally speaking, in order to make future population projections, the component method is used. It consists of adding the natural and the migration movement results to the original current pyramid; thus, a new population pyramid is being obtained.

As it can be deduced, the birth and death rates are the easiest variables to be calculated, as they are generally fixed by the sex and age start-up population structure itself. Oppositely, migrations are more time-variable phenomenon, as they not only depend on the demographic structure of the countries, both sending and receiving countries, but also on their socioeconomic situation.

For this reason, in most of the cases, more than one hypothesis is formulated from each one of these variables: births, deaths and migrations. Consequently, population projections usually have three scenarios: a middle one (also called tendential, since it is based on the extension of the recent observed trends) and two more scenarios, a low and a high one, in relation to the first one.

As it can be deduced from the previous paragraph, the obtained results from the population projections are strongly conditioned by the population juncture, since it actually determines the future dynamics. In addition, the projections usually have a strong ideological background, so they often help to anticipate the demographic dynamics. Due to all these reasons, the population projections are not intended to give an exact number of inhabitants or population structure; they should be seen as a theoretical exercise intended to predict the future evolution trends and not as a closed projection.

Hereafter, the 2008 projections of the United Nations Population Division are presented, as the latest so far, at global, continental, regional and country level, calculations. Three growth scenarios (low, middle and high) have been defined, taking into account the fecundity and death rates, the international migration movements and the HIV affectation.

Accordingly to this scenario, projected by the United Nations, there will be more than 9000 million inhabitants by year 2050, that is, a 35,47% increase over the year 2010. All the continents would increase their rates, except for Europe, that would have a 9,2% decrease. There would be a significant increase of 116,7% in Africa. Latin America would be the third on the list, ahead of Europe. There would be significant increases in North America, Oceania and Asia, where the 5000 million inhabitants rate would be exceeded.

The regional growth differences are also very noticeable at national level. Accordingly, the most significant growth would take place in the Sub Saharan African countries, which may double, triple or even quadruple their population between the 2010-2025: Uganda (383,27%), Niger (348,30%), Ethiopia (316,18%), Burkina Faso (292,02%), Zambia (285,07%) or Burundi (276,26%).

By contrast, most of the countries show more moderate and generally lower growth rates than those experimented so far. Thus, generally speaking, the world population growth rhythm has recently decreased, in comparison to the last decades. Therefore, there are nearly 100 countries that have a growth rate oscillating between 100% (i.e. a null growth) and 150% (a moderate growth): most of the North and South American countries, all North and Western Europe —except from Portugal— and some of the South-Eastern Asian countries, including India, the most populated country in the world by 2050, accordingly to the projections (some 1650 million inhabitants).

Lastly, a great number of countries (near 50) will lose population between 2010 and 2050: mainly the Central and Eastern European countries and most of the ex-Soviet republics. Japan is an outstanding case, as it can lose 30% of its current population in the next 40 years, if the predictions come true.

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