(March 2000) On January 13, the U.S. Census Bureau released its latest national projections on the size and composition of the United States. According to the middle series of these projections, which many feel represent the most likely scenario of future demographic trends, U.S. population, currently nearly 273 million, will approach 338 million in 2025, 404 million by 2050, and 571 million (more than double the current population) by 2100.

Of course, what actually happens with U.S. population in the 21st century will depend on future trends in fertility, mortality, and international migration. The projections released by the Census Bureau are based on differing assumptions on the levels of these three variables through 2100.

Take international migration. For the first time, the Census Bureau has made "dynamic assumptions" about migration. That is, the projections take into account current trends in migration and their likely future effects. This practice marks a break from the past, when Census Bureau demographers assumed that current levels would continue unchanged.

Current trends are a function of many factors, including the legalization and naturalization of many immigrants under the Immigration Reform and Control Act (IRCA) of 1986, which made these new citizens eligible to sponsor the immigration of their immediate family members; the decline in the flow of refugees (except for the former Yugoslavia); the rate of success of the United States in controlling its southwest border; and the emergence of South Asia, sub-Saharan Africa, and the Middle East as important sources of immigration.

The Census Bureau also has allowed the demographic characteristics of the projected total population — for instance, age structure — to influence the assumptions about immigration and immigration policy.

The result? A projected slight increase in immigration until 2003, as a result of the IRCA effect, followed by a decline — the influx from Yugoslavia having peaked that year or shortly thereafter — and then by a 40 percent increase between 2010 and 2030. The increase likely will raise immigration from 1 million to 1.4 million, where the number is projected to remain through the end of the century. The Bureau anticipates a new wave of migrants coming to fill jobs made vacant by the retirement of aging Americans. Because the overall population would still be increasing at that point, immigration's effect would diminish.

Despite these assumptions, the latest projections show only a slightly higher level of net immigration than the projections released in 1996. The reason is: Although the rate of emigration, particularly for the foreign-born, is projected to remain constant, the number of emigrants will increase as the foreign-born population increases.

One thing is certain: The Census Bureau cannot predict the future stability of foreign governments, the soundness of the global financial system, or sudden shifts in the availability of vital natural resources, all of which could affect immigration to the United States. The Census Bureau acknowledges that, unlike births and deaths, international migration has public policy as a major determinant.