The Impact of U.S. Immigration on Global Climate Change

By Edwin S. Rubenstein
Published in The Social Contract
Volume 27, Number 1 (Fall 2016)
Issue theme: "When robots replace humans"

On the first Earth Day, April 22, 1970, the nation paused to consider the impact of human activity on the global environment. The greatest threat seen that day was the prospect that continued global population growth would produce shortages of food, fuel, and natural resources.

Among the catastrophic forecasts made around that time:

• Paul Ehrlich, author of The Population Bomb, predicted that between 1980 and 1989, 4 billion people, including 65 million Americans, would starve to death.

Life magazine wrote, ... by 1985 air pollution will have reduced the amount of sunlight reaching earth by one half.

• Ecologist Kenneth Watt stated: “By the year 2000, if present trends continue, we will be using up crude oil at such a rate…that there won’t be any more crude oil.”

None of these prophecies came to pass:

• Mass starvation was averted by the development of high-yielding crop varieties, new irrigation infrastructure, modern manage-ment techniques, synthetic fertilizers, and other advances in agricultural technology known collectively as the “Green Revolution.”

• Global dimming gave way to a “brightening” trend when pollutants thought to prevent sunlight from reaching Earth declined in the decades following passage of the Clean Air Act in 1970.

• Increased fuel efficiency standards for automobiles, appliances, and building codes have cut oil consumption by about 50 percent below what would have been the case under pre-1970 standards. The only “shortage” in 2016 oil market lies in the capacity of tanks available to store excess oil.

Global warming? It was not on the environmental radar that first Earth Day. On the contrary, Kenneth Watt warned that: “The world has been chilling sharply for about twenty years. If present trends continue, the world will be about four degrees colder for the global mean temperature in 1990, but eleven degrees colder in the year 2000. This is about twice what it would take to put us into anice age.”1 This, of course, was another false alarm, the result of a slight downward blip in temperatures from the 1940s to the early 1970s and the failure of the mainstream media to cover a rapidly growing body of scientific literature projecting global warming due to greenhouse gas emissions.

In retrospect, the 1970s was a Golden Age for conservation, a period when most Americans believed that changes in our consumption habits, along with new energy saving technology, could control, or even reverse, environmental degradation. Reducing U.S. population growth was not considered necessary, or even desirable, in achieving that goal.

January 1, 1970, was a watershed moment. On that day President Nixon signed the single most important environmental statute in American history: The National Environmental Policy Act (NEPA). The new law ordered federal agencies to conduct Environmental Impact Statements (EISs) for any future actions — e.g., construction projects, programs, permits — that might “significantly” affect environmental quality. Unfortunately, NEPA never ordered Congress to study the potential impact of its own actions, especially liberalized immigration policies that are driving most of U.S. population growth.

How humans change the climate

Anthropogenic global warming — warming caused by human activities — comes primarily from the carbon dioxide (CO2) emitted by burning carbon-based fuels, principallythe gasoline used to power vehicles and the coal,oil, andnatural gas used to generate power for heating, cooling, and manufacturing. CO2 is also produced in nature by respiration, decomposition, combustion, and volcanic eruptions. In fact, the amount of carbon dioxide generated by natural processes is more than 20 times greater than that produced by human activity. Naturally generated CO2, however, is removed from the atmosphere by plants and forest growth (photosynthesis) and by the oceans, where CO2is dissolved and converted to carbonic acid.

Not until humans started large-scale use of natural combustion engines did CO2 become a problem. Carbon dioxide levels remained steady for the 10,000 years between the end of the last ice age and the start of the industrial revolution (about 1750). Human economic activity upset that delicate balance: CO2 concentrations have increased by 40 percent since 1750, according to an article published in 2016. In fact, current CO2 concentrations are above anything experienced on Earth during the last 800,000 years, according to reliable data that has been extracted from ice cores.2

Energy saving technology has reduced per capita carbon dioxide emissions since the first Earth Day. Total emissions are higher, however, because of population growth. This could have been avoided had the 1970 environmental law ordered Congress to study the impact of its own actions, especially the immigration laws that increased U.S. population growth.

As brought out below, our liberal immigration policy has triggered a massive transfer of population from countries with comparatively low per capita CO2emissions to one of the highest per capita CO2 emitters in the world. A more rational immigration policy could have reduced, if not reversed, the impact of U.S. population growth on the global environment.

Population is not the only factor, but…

Some environmentalists still argue that Americans need focus only on reducing pollution and consumption in order to curb environmental destruction. They are right to push for less consumption and increased energy efficiency, but wrong to assume such efforts can replace population control. A growing population can overwhelm improvements in energy efficiency and emissions abatement. Indeed, over most of our recent history reductions in energy use per capita and per dollar of GDP have failed to offset the increased numbers of “capitas.” Over the long run energy use and CO2emissions have risen steadily due to population growth.

Ecologists use a simple formula to illustrate impact of human activity on the environment:

I=P x A x T

In the so-called “IPAT” equation, I (the impact of human activity) is the product of three factors: P (total population), A (Affluence, as measured by GDP per capita), and T (the technology used to produce the goods and services measured in GDP.)

In the particular case of climate change, the following variation on the IPAT equation has been suggested:3

CO2 emissions= P x (GDP/population) x (energy/GDP) x (emissions/energy)

The CO2 equation tells us that while population is important, it is by no means the only factor driving emissions. Affluence, as measured by GDP per capita, also matters. The wealthier we become the more “stuff” we buy, and that stuff, whether cars, houses, vacations, etc., is produced by burning fossil fuels that emit CO2 into the atmosphere. Other things equal, a rapidly growing economy will generate more CO2 and other greenhouse gases than a slowing or shrinking economy.

But other things are never equal. Over the past four decades population has increased steadily, but the other three factors in the equation have either stumbled or are in long-term decline. Affluence, measured by GDP per capita, fell sharply in the Great Recession of 2008-09, and has not attained its pre-recession growth rates. The last two factors in the CO2 equation — energy usage per dollar of GDP and CO2 emissions per unit of energy usage — which together comprise the T, or technology, component — have also declined, reflecting the advances made in in energy saving technology:


From 1980 to 2014 total energy use increased from 78 quadrillion BTUs (quads) to 98 quads, an increase of 26 percent. Over the same period, however, real U.S. GDP increased by 149 percent.4 As a result the energy/GDP ratio — often called the “energy intensity” of the economy — declined by 49 percent from 1980 to 2014, and is projected to fall by another 42 percent by 2040.5


Reduced energy intensity is the result of many small and large efficiency gains since 1980, among them: a 25 percent improvement in fuel economy of passenger vehicles; a nearly 40 percent reduction in industrial energy use per unit of industrial output; a more than 25 percent reduction in energy lost in our electricity power grid; and a 70 percent reduction in energy used by new clothes washers. About 40 percent of the entire energy intensity decline is due to shifts in the U.S. economy away from energy intensive sectors (e.g., heavy manufacturing) towards services such as health care.6

By comparison, the fall in what we might call “emissions intensity” — CO2 emissions per unit of energy — has been fairly small: about 10 percent since 1980, projected to fall by another 6 percent from 2014 to 2040. The main factors influencing emissions intensity include substitution of natural gas for coal in electricity generation, the increased use of renewable energy, and improved emissions control systems in U.S. automobiles.

The upshot is that per capita CO2 emissions have been roughly flat or falling over the last four decades. If U.S. population had stabilized during that period CO2 emissions would have remained unchanged, or even declined. But that was not the case: U.S. population rose from 216 million in 1975 to 318 million in 2014, a gain of 102 million, or 47 percent.

Figure 2 (left column) depicts U.S. population growth and total CO2 emissions from 1975 to 2010.

Population and CO2 emissions moved more or less in tandem until the last several years when CO2 emissions fell as a result of the Great Recession of 2008 and its lingering aftereffects. This decline in the A, or Affluence, component of the IPAT equation is unlikely to continue. Eric Larsen, a research scientist at Princeton University’s Energy Systems Analysis Group, writes:

Recent declines in carbon emissions are the result of a combination of factors including the recession, increased natural gas production and the related decline in coal fired electricity generation, continuing improvements in efficiencies of energy use, and growth in renewables, particularly wind power. The recession, however, appears to be the most significant factor in the decline. Consequently, as the economy rebounds the fall in emissions is likely to be neutralized or overtaken by growing population and incomes…. In the face of such growth…modest improvements in energy efficiencies and expansions of lower carbon energy alternatives will not provide the level of change in the energy economy needed for carbon emissions to fall by 2050 to a level that most climate scientists believe is needed to avoid severe impacts of climate change.7

Bearing out Larsen’s prediction, emissions ticked up in 2013 and 2014, the latest years of available data:


Although emissions remain below pre-Great Rece-ssion levels, future population growth will inevitably reverse the CO2 downdraft. The latest Census Bureau projection — published in December 2014 — has U.S. population reaching 416.8 million in 2060. That is 98 million, or 31 percent, above the population reported for 2014. Immigration will account for about 65 percent of all population growth over this period. By the 2050s as much as 82 percent of annual population growth will be from this component.8

Immigration Drives CO2 Emissions

Progressives for Immigration Reform (PFIR), a Wasington, D.C.-based group devoted to immigration policy in the interest of American workers, has published an extensive study of the impact of immigration on U.S. population growth and the environment. The impact of U.S. CO2 emissions on global climate change is one of the issues explored in their report.9

The PFIR study is, in effect, an Environmental Impact Statement for U.S. immigration policy. As part of the their EIS, PFIR analysts developed three population projections corresponding to three reasonable immigration scenarios for the period 2010 to 2100:

• The No Action Alternative keeps immi-gration levels about where they are now, 1.25 million per year (legal and illegal immigration combined).

• The Expansion Alternative increases immigration by one million per year, to 2.25 million annually. This corresponds to the levels that would obtain under so-called “comprehensive immigration reform” cham-pioned by the Obama Administration and the Gang of Eight in the U.S. Senate. Population more than doubles, to 669 million in 2100, under this scenario.

• The Reduction Alternative reduces immigration by one million, to 0.25 million (250,000) per year. This is close to the levels prevailing before the 1965 Immigration Act triggered mass immigration into the U.S.

The No Action Alternative

The No Action Alternative would lead to a U.S. population of 524 million in 2100, an increase of 70 percent above the 309 million of 2010. Predicting CO2 emissions for the year 2100 under this — or any — immigration scenario is, of course, next to impossible. Accuracy depends on predicting how the three non-population variables in the CO2 equation on page 45 above will change over the 85-year projection period. The range of possibilities is daunting:


• GDP/population — The per capita income, or affluence, factor could range from a fraction of what it is today if the worst case scenarios envisioned by some ecologists and economists come to pass, to more than a four-fold increase if GDP per capita increases by a mere 2 percent over the next 85 years. This could easily imply a ten-fold variation between the best and worst economic growth scenarios, far greater than the roughly 2-fold difference between the low and high population projections evaluated in the PFIR’s EIS.

• Energy/GDP — This is more predictable than the other two non-population variables in the CO2 equation. As noted above, energy intensity fell 49 percent from 1980 to 2014, and EIA projects another 42 percent decline by 2040. It is reasonable to expect this downward trend to continue for the duration of the twenty-first century, although it will likely level off as technological breakthroughs become more costly and difficult to achieve.

• CO2 per unit of energy — This is the wildcard because it depends on the mix of energy sources rather than the aggregate amount of energy used. At present about 80 percent of our energy is derived by burning fossil fuels, which release CO2 into the atmosphere upon combustion. Less than 20 percent consists of nuclear energy and renewable sources such as hydropower, wind, solar, and biomass. It is inevitable that fossil fuels will increase in price as they become more difficult to find and extract, and, as a result, the share of energy generated by fossil fuels in 2100 will be far lower than at present.

Population is the only factor whose growth is “known” with certainty because it is fixed it in accordance with the immigration and demographic assumptions of the No Action Alternative scenario.

As stated above, U.S. population is projected to grow by 70 percent from 2010 to 2100 under this scenario. In other words, if there were no change in any of the three non-population factors, or if those changes cancelled each other out, CO2 emissions from the U.S. would be 70 percent higher in 2100. By comparison, climatologists claim that an 80 percent reduction in CO2 emissions by 2050, and their complete elimination by 2100, is needed to stabilize Earth’s temperature at, say, only two degrees above pre-industrial levels.10

At present about 25 percent of global CO2 emissions comes from the U.S. If the rest of the world embraced the No Action Alternative, the planet would face average warming of 4 degrees Celsius or more by 2100, according to the PFIR EIS.

What changes would occur in a 4 degree warmer world?

• A sea level rise of 20 to 39 inches by 2100 (this is in addition to a rise of several feet in coming centuries already locked in place by past warming).

• Existing water scarcity would worsen in many regions, particularly northern and east Africa, the Middle East, and South Asia. In Africa entire countries will face water shortages.

• Wildfires and species extinction on an unprecedented scale. The loss of biodiversity that would accompany a 4-degree warmer world would drive the Earth’s ecosystems to a condition “unknown in human experience.”11

• An increase of about 150 percent in the acidity of the ocean — “a rate of change unprecedented in the known history of the Earth.”

• Coral reefs may stop growing and actually start to dissolve. “The regional extinction of entire coral reef ecosystems, which could happen well before 4°C is reached, would have profoundly negative consequences for their dependent species as well as for the millions of people who depend on them for protein, income, tourism, and protection from waves and storms.”12

Two points need to be made. First, the 4 degree rise in average global temperature would not be evenly distributed. The largest warming would occur over land areas and would range from 4 to 10 degrees C. Average summer temperatures are expected to rise 6 degrees C (11 degrees F) across vast areas of the world, including the contiguous United States. Extreme summer heat waves will become “the new normal.”

Second, the accuracy of these projections is only as good as the climate models used to project those changes. Disruptive large-scale changes to the Earth’s ecosystem are generally not included in the climate modeling exercises used to develop the models or in impact assessments. A 4 degree rise in global warming could alter Earth’s ecosystem in ways that climate models are incapable of analyzing. Examples include the disintegration of the West Antarctic ice sheet, leading to more rapid sea-level rise than projected, or a large-scale die-off of the Amazon rainforest, potentially adding substantially to twenty-first century global warming from the loss of this colossal CO2 removal mechanism.13

The cumulative impact of the No Action Alternative is summarized in terms required in Federal Environmental Impact Statements:

Duration of Impact : Long-term to per-manent. The duration of the impact on CO2 emissions and climate change associated with the projected population growth under the No Action Alternative would range from “would likely last for a decade or more” to “indefinite or everlasting and for all intents irreversible.”

Extent of Impact: Large. The extent of the impact on CO2 emissions and climate change associated with the projected population growth under the No Action Alternative “would affect a resource on a regional, national, or global scale.”

Magnitude of Impact: Major. The mag-nitude of the impact on CO2 emissions and climate change associated with the population growth under the No Action Alternative would be Major, representing a “substantial impact or change in a resource area that is easily defined, noticeable, and measurable, or exceeds a standard.”

Likelihood of Impact: Probable. The impacts on CO2 emissions and associated with the population growth under the No Action Alternative are “more likely than not to occur, i.e., approximately 50% likelihood or higher.” While these impacts may be ameliorated partially by the other factors….discussed above, it is unlikely that these factors (improved energy and carbon efficiency) would be able to completely offset the adverse, overall effects of population growth on CO2 emissions and climate change.

The bottom line: “Overall, the net effect of the No Action Alternative on CO2 emissions and global climate change would be adverse, significant, and long-term.”14

The same dire conclusions apply to the Expansion and Reduction scenarios in PFIR’s EIS. Eighty-five years of cumulative population growth, no matter how large or small, will have devastating effects on global climate. The brutal reality is that a prolonged period of zero or negative population growth, combined with the phase-out of fossil fuels with renewable energy sources, may be required to reduce CO2 emissions.


The Reduction alternative offers one ray of hope, however :

“…under the Reduction alternative, in contrast to the No Action and Expansion alternatives, it would be far more feasible for the United States to make a constructive contribution to the global partnership urgently needed to address the climate predicament.”15

The implicit message: Only by reducing its own population growth will the U.S. be able to persuade the rest of the world to do likewise. Otherwise, global warming will go on unchecked.

All immigrants are not CO2 Equal

Over the long run U.S. population growth is the most important factor in CO2 emissions emanating from this country. Whether a new immigrant or a baby born to a U.S.-born mother, the number of children the new arrival chooses to have is far more important to 2100 climate than whether he or she recycles, bicycles to work, drives a hybrid vehicle, or sets the thermostat high or low.

In this sense, the act of immigrating is no different from the act of giving birth: both add a new source of future CO2 emissions from this country. Of course, had immigrants remained in their home countries they would have still produced some CO2, but their output would have been far less. Immigration to the U.S. represents a large-scale transfer of population to from countries with comparatively low per capita CO2 emissions to one of the highest per capita CO2 emitters in the world (left column).

The table shows that most of the top countries of origin of U.S. immigrants have far lower per capita CO2 emissions. This is not surprising, since most immigrants come here to improve their standard of living — the A, or affluence, factor in the IPAT equation — and this generally entails a higher level of energy consumption and CO2 emissions than if they had stayed home. Per capita CO2 emissions in the U.S. in 2013 were 4.2 times the average for the rest of the world (17.1 versus 4.1 metric tons.) As a result, immigration to the U.S. has an immediate impact on global CO2 emissions.

This is not say that new immigrants immediately generate as much CO2 as the average American. Income matters. there is a strong positive correlation between income and emissions. High-income Americans consume more fossil fuel than low-income Americans. They are more likely to own a car, live in unattached houses that take more energy to heat and cool, commute from distant suburbs, travel by airplane, and purchase goods and services with substantial energy embodied in their manufacture, production, and delivery. Low-income Americans and immigrants are more likely to live in apartments or other group quarters, carpool or take public transportation, travel less, and buy fewer consumer goods.

No governmental energy data source disaggregates U.S. CO2 emissions into the parts generated by native-born and immigrants. However, a study by the Center for Immigration Studies (CIS) used income differences as a proxy for differences in per capita emissions of the two groups.16 Their conclusion: immigrants earn about 85 percent as much as the average person (native-born and immigrant) living in the U.S. Applying this percentage to the 17.09 metric tons of CO2 generated by the average American in 2013, and multiplying by the 41.3 million immigrants living in the country that year, we estimate that immigrants generate about 600 million metric tons of CO2 annually, or about 11.1 percent of the U.S. total of 5,402 million metric tons in 2013. This is somewhat below their share of the population due to their lower average income.

It is useful to put the immigrant CO2 number into context. Six hundred million metric tons is roughly equal to the combined 2013 emissions of Argentina, Venezuela, Colombia, Chile, Ecuador, and Bolivia. It also equals the CO2 emitted by the United Kingdom, Ireland, and Sweden together.

If the 41.3 million immigrants living in the U.S. were a separate country, they would rank ninth in CO2 emissions, behind China, the United States, India, Japan, Russia, Germany, South Korea, and Iran.

Had they remained in their country of origin, and emitted CO2 at the average rate for persons in those countries, we estimate their CO2 emissions in 2013 would have been only 167 million metric tons. This represents a reduction of 433 million, or 72 percent, below the 600 million tons they emit in this country.

The net impact of U.S. immigration on global CO2 emissions — 433 million metric tons in 2013 — represents 1.3 percent of that year’s global emissions, and 3 percent of the increase in global emissions since 1980. By contrast, the 41.3 million immigrants living here in 2013 represented only 0.6 percent of the Earth’s population.


When it comes to global warming, U.S. environ-mentalists have focused on policies aimed at curbing new sources of fossil fuels, increasing the efficiency with which fossil fuels are used, and encouraging the use of renewable fuels such as wind, solar, and battery power. They have studiously avoided the “demand” side of the energy equation, the role U.S. population growth plays in increasing the demand for goods and services requiring energy.

Per capita CO2 emissions are significantly higher in the U.S. than in most other countries in the world. A growing population can overwhelm improvements in energy efficiency and emissions abatement. Indeed, for most of our recent history reductions in energy use per capita and per dollar of GDP have failed to offset the increased demand for energy brought on by population growth.

Over the long run U.S. population growth is the most important factor in CO2 emissions emanating from this country, and immigration is likely to be the main determinant of how fast our population grows. 


1. Wikipedia, Earth Day

2. T.J. Blasing, Recent Greenhouse Gas Concentrations, Carbon Dioxide Information Analysis Center, April 2016.

3. Progressives for Immigration Reform (PFIR), United States Immigration Policy Environmental Impact Statement, October 2015. Page 3-201.

4. American Council for an Energy Efficient Economy, Energy Efficiency in the United States, 35 Years and Counting, June 2015.

5. EIA, Annual Energy Outlook 2015.

6. American Council for an Energy Efficient Economy, op. cit., p. iv.

7. Eric Larsen, Can U.S. Carbon Emissions Keep Falling? Climate Central, October 2012.

8. Edwin S. Rubenstein, Immigration Drives U.S. Population Growth, NPG Forum Paper, January 2016.

9. Progressives for Immigration Reform (PFIR), United States Immigration Policy Environmental Impact Statement, October 2015. Page 3-200.

10. PFIR, op. cit., page 3-209.

11. PFIR, op. cit., page 3-212.

12. World Bank, Turn Down the Heat: Why a 4 Degree Warmer World Must be Avoided. A Report for the World Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics, November 2012, page xv.

13. ibid., p. 60.

14. PFIR, op. cit., page 3-213.

15. PFIR, op. cit ., page 3-218.

16. Leon Kolankiewicz and Steven Camarota, Immigration to the U.S. and World-wide Greenhouse Emissions, Center for Immigration Studies, August 2008.

About the author

Edwin S. Rubenstein, a regular contributor to The Social Contract, is president of ESR Research, economic consultants. As a journalist, Mr. Rubenstein was a contributing editor at Forbes and economics editor at National Review, where his “Right Data”column was featured for more than a decade. He is the author of  The Earned Income Tax Credit and Illegal Immigration: A Study in Fraud, Abuse, and Liberal Activism.

Copyright 2007-2013 The Social Contract Press, 445 E Mitchell Street, Petoskey, MI 49770; ISSN 1055-145X
(Article copyrights extend to the first date the article was published in The Social Contract)