The UN Population Division on Replacement Migration

The most salient demographic trend pictured by the influential set of population projections prepared by the Population Division of the United Nations (a unit in the UN's Department of Economic and Social Affairs) is the continuing substantial increase—albeit at a declining rate—of the global population during the coming decades. According to the “medium” variant of the most recent (1998) revision of these projections, between 2000 and 2050 the expected net addition to the size of the world population will be some 2.85 billion, a figure larger than that of the total world population as recently as the mid‐1950s.All of this increase will occur in the countries currently classified as less developed; in fact, as a result of their anticipated persistent below‐replacement levels of fertility, the more developed regions as a whole would experience declining population size beginning about 2020, and would register a net population loss of some 33 million between 2000 and 2050.A report prepared by the UN Population Division and released on 21 March 2000 addresses some of the implications of the changes in population size and age structure that low‐fertility countries will be likely to experience. The 143‐page report, issued under the eyecatching title Replacement Migration: Is It a Solution to Declining and Ageing Populations?, highlights the expected magnitude of these changes by the imaginative device of answering three hypothetical questions. The answer to each of these questions is predicated on the assumption that some specified demographic feature of various country or regional populations would be maintained at the highest level that feature would exhibit, in the absence of international migration, in the United Nations' medium population projections (as revised in 1998) during the period 1995–2050. The selected demographic features are total population size, the size of the working‐age population (15–64 years), and the so‐called potential support ratio: the ratio of the working‐age population to the old‐age population (65 years and older). The illustrative device chosen for accomplishing the specified feats of preserving the selected demographic parameters (i.e., keeping them unchanged up to 2050 once their highest value is attained) is international migration. Hence the term “replacement migration.”Given the low levels of fertility and mortality now prevailing in the more developed world (and specifically in the eight countries and the two overlapping regions for which the numerical answers to the above questions are presented in the report), and given the expected future evolution of fertility and mortality incorporated in the UN population projections, the results are predictably startling. The magnitudes of the requisite compensatory migration streams tend to be huge relative both to current net inmigration flows and to the size of the receiving populations; least so in the case of the migration needed to maintain total population size and most so in the case of migration needed to counterbalance population aging by maintaining the support ratio. Reflecting its relatively high fertility and its past and current record of receiving a large influx of international migrants, the United States is a partial exception to this rule. But even for the US to maintain the support ratio at its highest—year 1995—level of 5.21 would require increasing net inmigration more than tenfold. The country, the report states, would have to receive 593 million immigrants between 1995 and 2050, or a yearly average of 10.8 million. The extreme case is the Republic of Korea, where the exercise calls for maintaining a support ratio of 12.6. To satisfy this requirement, Korea, with a current population of some 47 million, would need 5.1 billion immigrants between 1995 and 2050, or an average of 94 million immigrants per year. (In the calculations, the age and sex distribution of migrants is assumed to be the same as that observed in the past in the main immigration countries. The fertility and mortality of immigrants are assumed to be identical with those of the receiving population.)The “Executive Summary” of the report is reproduced below, with the permission of the United Nations. Chapters of the full report set out the issues that prompted the exercise; provide a selective review of the literature; explain the methodology and the assumptions underlying the calculations; and present the detailed results for the eight countries and two regions selected for illustrative purposes. A brief discussion of the implications of the findings concludes the report. As is evident even from the figures just cited, immigration is shown to be at best a modest potential palliative to whatever problems declining population size and population aging are likely to pose to low‐fertility countries. The calculations, however, vividly illustrate that demographic changes will profoundly affect society and the economy, and will require adjustments that remain inadequately appreciated and assessed. The criteria specified in the UN calculations—maintenance of particular demographic parameters at a peak value—of course do not necessarily have special normative significance. Past demographic changes, with respect notably to the age distribution as well as population size, have been substantial, yet they have been successfully accommodated under circumstances of growing prosperity in many countries. But the past may be an imperfect guide in confronting the evolving dynamics of low‐fertility populations. As the report convincingly states, the new demographic challenges will require comprehensive reassessments of many established economic and social policies and programs.