Every two years, the United Nations Population Division publishes updated data on the population structure and development in the countries of the world. The most recent update took place in 2004. This dataset contains estimates of the demographic parameters from 1950 to the present day, as well as projections until 2050 in various variants.

The UN estimate calculated by the medium variant is that the world's population will grow to 9.076 billion people by 2050. This corrects upwards the estimate of the previous 2002 Revision by about 160 million people. This correction is the result of life expectancy which is increasing worldwide, as well as of an average number of children which is higher than that estimated in 2002. In particular, the future decline in the average number of children in Africa was obviously overestimated in the 2002 Revision.

The world's population is being influenced by the following individual trends:

• The population shares will shift in the 100 years from 1950 to 2050, clearly favouring the less developed countries in Asia and Africa, whilst the share of the world population accounted for by developed countries is continually decreasing. The least developed countries, in particular those in sub-Saharan Africa, show the highest numbers of children and the most rapid population growth. The countries of eastern Europe and the successor states of the Soviet Union are subject to the most marked shrinking processes.
• The challenge with rapidly-growing or shrinking populations lies not only in rising or falling population sizes, but in particular in the change in the age structure which is associated with this trend. Rapidly-growing populations have a number of young people which grows from one birth cohort to the next who have to be fed, clothed, trained and provided with jobs; shrinking populations have a growing share of elderly people who have to be taken care of.
• The world population is ageing overall because fertility is falling in most countries in the world. The most rapid decline is in China, since China has pursued a rigorous one-child policy since the end of the seventies. The strict restriction of the average number of children there has led since then to a continuous fall in the sizes of birth cohorts. The share of children and young people among the total population will have fallen considerably in 2050, and China will face the problem of a considerable expansion in the older birth cohorts - demographic ageing. The population ages as a consequence of the political goal of slowing demographic growth.
• More children will be born to women in all age classes in the less and least developed countries than in the developed countries. The age class in which most children are born will change in line with the state of development, in parallel with the fall in the number of births per woman. In the less developed countries, most children will be born to women aged between 20 and 24; in the more developed countries, this applies to women aged 25 to 29. A fall in the average number of children per woman hence means above all that young women have fewer children.
• Life expectancy is higher the further socio-economic development is advanced. It is highest in the industrialised countries (the inhabitants of Japan currently have the highest life expectancy), and lowest in the least developed countries.
• The gap in the life expectancy of women and men also generally increases along with life expectancy, “biological factors accounting for roughly 1-2 years of the gap in life expectancy between the sexes”, favouring women (Luy 2002: 119). In the industrialised countries, women’s advantage over and above this is the result of social, economic and cultural factors. Men there are more affected by the consequences of violent crime, accidents and unhealthy conduct (such as smoking) than women. In the developing countries, a less pronounced advantage, or indeed a disadvantage, is the result of women’s poorer living conditions, for instance when it comes to food or medical care, and in particular the dangers posed by childbirth.
• The developed countries are the main destination regions of international migration. Their migration balance per 1,000 inhabitants increased between 1950 and the end of the last century. The least developed countries were migrants’ main regions of origin per 1,000 inhabitants in the past, although the balances fluctuated widely. In the future, the UN presumes that migration per 1,000 inhabitants from the least developed countries will be less overall than that of the developing countries. There is evidently no close link between the rate of natural population growth and net migration.