Immigration will be the key factor determining whether populations in the developed world increase or decrease over the coming century. Newly published policy-based population projections illustrate this for the United States.
by Philip Cafaro
Population size helps determine human societies’ environmental impacts. Given that immigration is a key factor influencing the size of human populations, environmentalists seeking to create sustainable societies have a prima facie stake in immigration policy. In many developed countries, decades of below-replacement fertility levels have not led to population stabilisation or decline. Instead, increased immigration has resulted in continued population growth in the United States, Canada, Australia, France, the United Kingdom, Sweden, the Netherlands and many other wealthy countries.
How important will immigration be in determining future U.S. population sizes? An article I recently published in the Journal of Population and Sustainability seeks to answer this question by developing population projections under alternative possible immigration scenarios. Using demographers’ standard “cohort-component” projection method and fertility and mortality settings from the most recent (2023) U.S. Census Bureau projections, I varied net migration between 2025 and 2100 to create new projections based on alternative policy scenarios.
Recent immigration policy
Recent variations in U.S. immigration levels have been due to policy changes. Legal immigration under Congressionally mandated programs has stayed relatively stable at around 1.2 million annually, not just during the Trump and Biden administrations but ever since the last major increases in legal immigration levels in the early 1990s. What changed dramatically during the past decade have been four things: decreased (Trump) and then increased (Biden) tolerance for illegal immigration; the Covid pandemic; an immense surge in political asylum applications by economic migrants; and new ‘temporary’ parole programs bringing in several million citizens from distressed states in Latin America.
In 2017, the Trump administration became the first Republican administration since the 1950s to seriously attempt to reduce illegal immigration. Efforts included the ‘Remain in Mexico’ policy, under which asylum applicants entering the U.S. illegally were returned to Mexico to await adjudication of their claims; increased enforcement of employer violations of worker visa programs; a temporary suspension of foreign aid to several Central American countries to compel them to cooperate with repatriation efforts; and more. These endeavours garnered mixed success, yet they did reinforce the ideas that limiting immigration is necessary and that immigration limits should be enforced. Illegal immigration into the U.S. decreased somewhat during Trump’s first term, while legal immigration levels remained steady. Covid-19 did more to reduce overall immigration levels, however, with 2020 recording some of the lowest numbers seen in decades.
In response, in 2020 the Biden team went further than any modern American administration in relaxing immigration enforcement. 850,000 visitors overstayed their visas and remained in the U.S. illegally in 2022. Nearly 1.4 million prima facie inadmissible migrants were released by federal officials into the country in fiscal year 2023, many after filing bogus political asylum claims. During the administration’s first three years, two million people from faltering and failed states were ‘paroled’ into the U.S. under special programs originally designed to accommodate a few hundred people. More recently, after public outcry and with an impending Presidential election, these numbers were brought down. But they represent an unprecedented increase in illegal and quasi-legal immigration which, added to stable levels of legal immigration, has led to the highest absolute net migration levels in US history.
New policy-based population projections
Clearly, Americans and America’s major political parties have sharply diverging views regarding proper immigration levels. We can compare three scenarios that begin to capture the range of immigration policy choices facing the United States (Figure 1 below).
Holding fertility and mortality rates steady across all three scenarios, we first graph a rough ‘status quo’ scenario of 1.5 million annual net migration, the average over the eight administrations of the past five U.S. presidents from 1992 to the present. Projected forward, this immigration level leads to substantial population growth throughout this century. We then compare this scenario to one based on the immigration levels recommended by the U.S. Commission on Immigration Reform (1997) (commonly known as the Jordan Commission) and endorsed by President Clinton (300,000 annual net) and to the highest annual net immigration level under the Biden administration (approximately 3 million). The Jordan Commission recommendations have been endorsed by numerous advocacy groups; they reduce immigration levels substantially, while leaving some room for bringing in exceptional workers, genuine political refugees, and spousal reunification. The Biden administration’s numbers for 2023 stand as the high-water mark for immigration permissiveness, providing an empirically-grounded high-migration comparison to the status quo scenario.
As you can see, these three policy scenarios put the United States on three very different population trajectories: rapid growth, gradual growth, or gradual decline. They differ in their 2100 population projections by 330 million – very close to the entire U.S. population today! Here we see that at a first approximation, immigration policy is population policy in the United States, as it is throughout most of the developed world. The environmental difference between a population of 615 million or 285 million in 2100 would be immense, impacting everything from carbon emissions to urban sprawl, air pollution to water withdrawals from our rivers and streams, habitat preservation for endangered species to housing costs and crowding for American citizens.
All else being equal, we can assume that 615 million Americans will make more than twice the economic demands and inflict more than twice as much ecological damage as 285 million Americans. Furthermore, these populations would continue increasing or decreasing after 2100, if their respective immigration, fertility, and mortality trends continued. This in turn would move Americans even further away from or further toward ecological sustainability.
Seven generations
Figure 2 below extends our three immigration policy scenarios out another hundred years to 2200. From where we sit now, this is looking out the ‘seven generations’ that far-seeing leaders of the Iroquois Confederacy traditionally were supposed to scan when making important public decisions (assuming 25 year-long generations). What do we see? Three radically different population futures.
Under the status quo scenario (1.5 million annual net migration), the U.S. population grows slowly during the rest of this century and stabilises over the course of the next one. But it stabilises at over one hundred million more Americans than today (445 million in 2200). Accepting hundreds of millions of immigrants over this period could incentivise continued population growth in sender countries, since large families are likely to derive more support from overseas remittances, a major economic factor in many developing countries. The status quo scenario does not appear sustainable.
Under the high-level immigration scenario (3 million net annually), the U.S. population continues to grow rapidly during the next two centuries, ballooning to nearly 800 million people with no end to growth in sight. Long before 2200, the American experiment may have come to an end, whether from ecological catastrophe or social unrest, amplified by growing ethnic divisions and an unravelling economic safety net. This choice seems even less likely to be sustainable.
Finally, under the low immigration scenario (300,000 annually), the U.S. population declines by half by 2200 to 168 million. Of course, by itself such population decline would not guarantee sustainability – U.S. citizens could try to use the ecological space freed up to engage in even greater per capita hoggishness. Even 168 million Americans still seems likely to remain unsustainable, given high levels of per capita resource use. But as part of comprehensive efforts to create a sustainable society, the potential benefits of halving the U.S. population would be immense. An America closing in on 150 million (rather than 800 million!) could use less water, generate less air and water pollution, and take less habitat from other species. In fact, it would be in prime position to restore degraded ecological lands, particularly agricultural lands no longer needed to feed so many human beings. This is the only potentially sustainable path of the three.
Conclusion
Physicist and population activist Al Bartlett used to regularly tell listeners that human beings’ biggest intellectual liability is our inability to appreciate the power of exponential growth. While a million more or less in annual immigration may seem unimportant for a continental nation with a total population of 340 million, its impact cumulates quickly. For additional projections and a deeper delve into US immigration policy, see the full paper, “The impact of immigration policy on future US population size.”
Of related interest:
- U.S. Census Bureau, “Net International Migration Drives Highest U.S. Population Growth in Decades,” December 19, 2024.
- New York Times, “Recent Immigration Surge Has Been Largest in U.S. History,” December 11, 2024.
- Philip Cafaro and Patricia Dérer, “Policy-based Population Projections for the European Union: A Complementary Approach.” Comparative Population Studies 44 (2019): 171-200.
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