As many of the readers of this space undoubtedly will have come to realize; yours truly is a bit of a demographics wonk which probably goes a long way to characterize him except for the obvious fact that he is also, above all, an econ wonk.

As part of my upcoming master's thesis I am naturally trying to combine these traits and it should come as no surprise that the focus is on demographics and international capital flows. That will not be the topic of this entry however. Rather, I thought that I would plug a recent paper on global ageing (1) by Wolfgang Lutz Warren C. Sanderson, and Sergei Scherbov published in the brand new journal, Journal of Population Ageing, edited by the team of demographers, Sarah Harper and George Leeson, at the Oxford institute of Ageing (Oxford University). Also, this would naturally be a nice occasion to ever so slowly reveal what I am arguing in the context of my own research; research which is naturally heavily affected by the likes of Lutz, Malmberg, Lee, McDonald and other of our time's great (econ)-demographers. (Graphs are made by the author and not taken from Lutz et al.)

With respect to Lutz et al they set out to grapple with one of the most difficult issues in the context of demographics and ageing in the form of our ability to forecast the future trends of ageing in the context of the global economy and different regions. The main conclusions indicate a rapid and, in some cases, accelerating process of population ageing in a global context in the next decades as well as a the very likely outcome that global population growth will cease to exist as a lingering phenomenon in the century which follows. Here is their abstract;

Population ageing is, in the first instance, a demographic phenomenon; although its consequences go far beyond demography. But the future trends of ageing are not yet known and many of the consequences of ageing will depend on the future speed and extent of ageing. Here we summarize what is already known and what is not yet known about future ageing trends in different parts of the world. We do this through the means of new probabilistic population forecasts. The section ‘New Regional and Global Probabilistic Population Forecasts’ presents the results of those forecasts. They confirm the earlier finding (Lutz et al., Nature, 412(6846), 543–545, 2001a) that it is highly likely that the world’s population growth will come to the end during this century. The following four sections present results for proportions of populations 60+, old age dependency ratios, proportions 80+ and average ages. In the section ‘New Measures of Ageing’, we analyse a new measure of ageing that takes life expectancy changes into account.

The first question which immediately springs to mind (or at least it did to me) is first and foremost what kind of techniques the authors are using in their endeavors to actually make forecasts on a variable as complex as ageing and so far into the future. Well, this is also where water gets muddied since it is important to realize, a priori, the amount of uncertainty which are attached to the kind of exercise Lutz et al. embark on. As most of you will know ageing is driven by the joint process of declining fertility and increasing life expectancy (and to some extent migration) and once we use this break down to operationalize ageing it gets dreadfully difficult to forecast although there are tentative conclusions which can be drawn based on existing evidence. In this way, it is important to dwell at the main conclusion, namely that the world as a whole is set to age rapidly before heading off into more specific forecasts.

The formal technique used by Lutz et al. is probabilistic forecasting which is basically a technique of collecting random draws from existing data on fertility, mortality and migration in order to produce a series of potential distributions and paths which can ageing can take as we move forward. Lutz et al. center on five simulations. The first in the context of total population size, the second on the proportion of people aged 60+, the third focuses on dependency ratios, the fourth turns the attention to the proportion of people aged 80+ and the final simulation centers on average age.

In relation to the first simulation which focuses on population growth it appears certain that the global population will continue to grow up until 2030-2050 depending on the path you look at. Beyond that point the simulations become extremely insecure ranging from a continuation of population growth to a decline in population growth which will restore the global population level at its 2000 level in the year 2100. Needless to say that such exercises are largely pointless from the point of view of inference about e.g. economic effects. However, what seems to survive as a main conclusion is that it is very likely that the tendency of population growth will come to an end some time during the next century, something which is significant in its own right in a world where the discourse on global warming, in my opinion, risks to engender policy advice to emerging economies which are essentially ill informed.

With respect to the paper in general I take away the following points in random order.

• The potential importance of migration. In this regard, it is worthwhile to have a look at the simulated path for population growth (and thus in some sense the change in age structure) for Eastern Europe and Sub-Saharan Africa.