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immigration were halved, to 410,000 per year, growth would be slower, but the population would still rise to 349 million by the middle of the next century. If, on the other hand, net immigration were to increase by half, to 1,230,000 a year, the population would rise to 426 million by 2050. In either policy scenario, the population will be different from that under the medium immigration assumption—and by more than the simple addition or subtraction of immigrants, since the descendants of these immigrants will also be part of the future nation.
Although, in light of the current debate, very high immigration is not a realistic policy option, Table 3.3 also illustrates population growth under that scenario. The outcome is a steady increase to 463 million in 2050.22
Components of Change
What underlies the effects the various immigration scenarios have on population? Although the five immigration scenarios in the population projections assume a constant annual number of net immigrants, the annual net immigration rate23 will change as the population grows. That rate is one of the two elements in the rate of population growth; the other is the rate of natural increase—that is, the crude birth rate minus the crude death rate. Table 3.4 lists crude birth and death rates as well as the rate of natural increase under our five alternative immigration scenarios. We first examine the contribution of net immigration to annual population growth.
Besides simply adding people to the population, immigration has other repercussions for population change. By shifting the age-sex composition of the population, immigrants alter the likelihood of all residents of dying or having children. Immigrants may have a different age distribution from other residents, or they may have different childbearing rates, and thus they may affect the number of deaths and births.
In the absence of net immigration, the crude birth rate would decrease between 1995 and 2050, the crude death rate would increase, and the rate of natural increase would decline to zero (see Table 3.4). These results would occur because the population would slowly become older, with a smaller proportion in the childbearing ages (15 to 44) and a greater proportion in the higher mortality ages (65 and over).
After rising a bit through the end of this century, the rate of increase will ease back to levels not much above the current rate.
The net immigration rate is sensitive to assumptions about the annual number of net immigrants. That rate varies in the years 1995-2000 between 0 and 6 per 1,000. Over time, however, as the population increases, the rate falls for all the assumptions about immigration. Under the medium assumption, for example, it decreases from 3 per 1,000 in 1995-2000 to 2 per 1,000 in 2045-50. Even very high immigration yields a net immigration rate of less than 4 per 1,000 by 2045-50.