Demographic developments have played an important role in the structure and functioning of the Earth's system. The exponential population growth of the last century has led to high pressures on the environmental system, with the issue of hunger as representative of harmful effects. Despite the fact that the population growth is currently negative in some of the world's regions, the world population is expected to increase, at least in the next couple of decades.
Looking at the three basis components of the demographic changes, fertility, mortality and migration, one can better understand the dynamics and changes in size and structure of future populations. De simultaneous developments of these components are known as the demographic transition theory. There are several institutions involved in developing and publishing population projections. The Population Division of the United Nations is possibly the best known institution, responsible for population projections up to 2050 for the majority of countries in the world. In addition to the UN projections, other projections are made on the national (e.g. the Netherlands) and regional scales (e.g. European).
However, with different institutions developing projections at different aggregation levels, inconsistencies over the various geographical scales are almost inevitable. Furthermore, rock-solid sets of assumptions are often lacking, and uncertainties are only included by the definition of high, medium and low variants. One of the ways to deal with uncertainties may be application of a scenario. Instead of covering up uncertainties with rather meaningless variants, a scenario methodology allows one or more consistent images of the future to be created. The IPCC has applied this methodology to gain better insights into future emission paths, resulting in an advanced and useful set of scenarios.
In this approach, the two most relevant trends to cover most of the future uncertainties have been distinguished. These trends are globalization versus regionalization, and individualism/market orientation versus collectivity. Their combination will result in four scenarios.The scenario approach has been applied to three aggregation levels, the Netherlands, Europe and the 17 major world regions. In these applications the assumptions on fertility, mortality and migration are, to the furthest extent, based on the underlying socio-economic and environmental determinants. By using the same methodology in all applications, a set of scenarios is created that is consistent for the various geographical scales. The associated simulation results show an assorted set of images of the future population.