PAI Logo Population Action International
1120 19th Street, N.W. Suite 550,
Washington, D.C. 20036 (202) 659-1833
PAI Logo

Stabilizing the Atmosphere:
Population, Consumption and Greenhouse Gases

By Robert Engelman

Population and Environment Program
Population Action International


Table of Contents
I. Atmospheric Overload

The Greenhouse Gases
Human Influence
Evidence of Change
Population, Deforestation and Greenhouse Gases

II. Considering Population’s Role

Past Analyses
Analytical Challenges
The Legacy of the Past
China and Carbon Dioxide Emissions

III. A Stabilization Model

A Model of Equitable Stabilization
Reducing Consumption, Sustaining Quality of Life
Global Versus National Population
The United States and Carbon Dioxide Emissions
Consumption and Overconsumption

IV. Strategies

Reducing Consumption
Population and Sustainability
Population and Human Development
Responding to the Challenge

Appendix 1: Data Sources and Methodology
Appendix 2: Countries’ Per Capita 1990 Carbon Dioxide Emissions
from Fossil Fuel and Cement Production
Appendix 3: People, Carbon Dioxide and a Stable Atmosphere: A Ranking of 126 Countries by 1990 Per Capita Emissions of CO2 (164 K)
List of Boxes

The Earth’s Atmosphere and Population
Population, Deforestation and Greenhouse Gases
China and Carbon Dioxide Emissions
The United States and Carbon Dioxide Emissions
Consumption and Overconsumption

List of Figures

Figure 1: The Greenhouse Effect
Figure 2:
Relative Contributions of Greenhouse Gas Emissions from Human Activities to the Greenhouse Effect During the 1980s
Figure 3:
The Growth of Carbon Dioxide Concentrations in the Atmosphere Since 1958
Figure 4:
World Population and Carbon Dioxide Emissions: 1860-1990
Figure 5:
Carbon Dioxide Emissions by Region, 1950 and 1990
Figure 6:
Global Per Capita Carbon Dioxide Emissions: 1860-1990
Figure 7:
World Population, 1990-2150: Three Projections


The Earth’s Atmosphere and Population

Range of atmospheric greenhouse gas concentrations from the dawn of the human species to 1750:

Carbon Dioxide (CO2): 180-295 parts per million
Methane (CH4):
0.3-0.8 parts per million
Nitrous Oxide (N2O):
275-295 parts per billion
(Compound not yet invented.)
(Compound not yet invented.)

Atmospheric greenhouse gas concentrations and rates of increase in 1990:

Carbon Dioxide (CO2): 353 parts per million (25 percent increase from preindustrial levels; annual growth rate is 0.5 percent)
Methane (CH4):
1.72 parts per million (115 percent increase from preindustrial levels; annual growth rate is 0.5-1 percent)
Nitrous Oxide (N2O):
310 parts per billion (9 percent increase from preindustrial levels; annual growth rate is 0.25 percent)
280 parts per trillion (annual growth rate is 4 percent)
484 parts per trillion (annual growth rate is 4 percent)

World population, 1750:
760 million people

World population, 1990:
5.3 billion people (annual growth rate is 1.6 percent)

World population, 2050 (projected):
Between 7.8 and 12.5 billion people




Humanity and climate are interconnected. A prehistoric climate shift that turned moist forests into dry savannas in Africa may have sparked the evolutionary shift to upright walking.2 Rainfall, temperature and sea level have always governed where people live, trade and grow their food. People also influence climate, defined as the prevailing or average pattern of weather. And as we approach a new millennium the growing scale of human activity threatens to raise global average temperatures through the emission of gases that amplify the greenhouse effect, which traps solar heat in the lower atmosphere.

The physical laws governing the greenhouse effect are well understood, and there is no question the atmosphere’s capacity for trapping heat is growing stronger as a result of human activities. Nonetheless, to consider how changes in human population could influence climate change is to bring together two of the most controversial environmental topics. The exact timing, magnitude and impacts of global warming remain uncertain and subject to intense debate—as does the role of population growth in any environmental problem. The word population is not even mentioned in the Framework Convention on Climate Change, an international treaty ratified by 57 countries that went into effect in March 1994.

This is perhaps not surprising. Any discussion of population’s role in greenhouse gas emissions faces an immediate challenge: How can climate change be attributed in any way to population when individual resource consumption occurs disproportionately in industrialized countries that account for only a very small portion of the world’s population growth? The average resident of the world’s wealthier nations, such as the United States, sends hundreds of times more heat-trapping carbon dioxide (CO2) into the atmosphere than the average resident of the least-developed countries, such as Nepal or Chad. What, then, is the case for acting to slow population growth to reduce the risk of climate change?

This report, the second in a series on population and critical natural resources that began with an examination of renewable fresh water, attempts to answer such questions. It argues that the atmosphere is a finite global resource, whose critical role in regulating global climate increasingly is influenced by humanity’s use of the air for disposing of a particular type of waste—greenhouse gases. International cooperation will be needed to allocate equitable disposal rights. If nations cannot agree, the risk will continue to accumulate, and the planet’s climate may simply keep getting hotter with no end point in sight. Consensus is more likely if nations acknowledge that human beings in principle have an equal right to use the atmosphere. If so, stabilizing world population size at a lower rather than a higher level increases the likelihood that tolerable levels of individual resource consumption will be compatible with equity and a stable climate, and thus sustainable.

This argument applies to industrialized countries, most of which still have growing populations, and to less developed ones. Only global population stabilization will preserve the portion of the atmosphere available to each individual. Ironically, to explore this concept is also to illuminate how much many of us exceed even our current fair share of the atmosphere’s absorptive capacity in consuming such resources as fossil fuels.

The atmosphere's capacity for tolerating carbon dioxide emissions without risk is something for which sustainability can be quantified.

Although a number of greenhouse gases are addressed, the study chiefly examines industrial carbon dioxide emissions—those from the combustion of fossil fuels and the manufacture of cement—for which there is country-by-country data going back four decades. (Cement production, responsible for two percent of the total, releases the gas as a byproduct of the processing of limestone.) The focus is on 1990 because it is the latest year for which there is authoritative data for both population and industrial CO2 emissions by country. Carbon dioxide is the dominant gas in human alteration of the atmosphere, and industrial emissions its major source.

Carbon dioxide emissions from deforestation, which are significant, are considered conceptually but not included in the calculations, chiefly because there are no comparable country data series. As a result the calculations necessarily overstate the current role of industrialized countries in altering the atmosphere, but the analysis of population’s role is not qualitatively affected. The historical emissions of industrialized countries, from both fossil fuel use and deforestation, also are not directly addressed.

Unless otherwise indicated, references to "climate change" in this report refer to human-induced climate change, which is currently pushing global climate toward progressively warmer conditions. The study assumes humanity will at some point attempt to stabilize atmospheric concentrations of greenhouse gases, thus stabilizing the long term human influence on climate. That may not happen for some time, but the study uses 1990 as a convenient reference year. While humanity may continue to load the atmosphere with CO2 and other greenhouse gases for many years, the practice is not sustainable, since neither humanity nor natural ecosystems will be able to tolerate forever a climate being pushed toward ever warmer temperatures. Nor is it equitable, since many of the countries least responsible for greenhouse gas emissions are also least capable of adapting to the likely consequences of human-induced climate change.

To explore relationships among population, consumption and greenhouse gas emissions, the study develops a model to illustrate how an international agreement might be designed to stabilize atmospheric CO2 levels based on the principle of equal access to the atmosphere, and how population and consumption dynamics would affect this effort in different ways. The equal right of all human beings to the seas—which, like the atmosphere, are a global "commons"—is enshrined in the Law of the Sea convention, effective in late 1994. Similarly, the two key principles recognized by hundreds of international agreements on fresh water are equitable access to the resource and a prohibition against one state harming another by its actions.3 Both of these principles are logically applicable to the atmosphere.

Stabilizing CO2 emissions, a near term goal of the Climate Convention, would not stabilize CO2 concentrations, which would still increase by nearly half between now and the year 2100.4 Central to the analysis presented here is the question: If everyone in the world had an equal right to emit carbon dioxide into the atmosphere, how generous could that right be if the sum total of all emissions had to keep CO2 concentrations stable—especially as world population continues growing?

The atmosphere’s capacity for tolerating carbon dioxide emissions without risking a substantial human alteration of climate is something for which sustainability can be quantified. The study’s centerpiece chart features a ranking of 126 countries with populations of over one million people, based on their 1990 per capita emissions of industrial carbon dioxide. These figures are compared with the global per capita average emission that would be required to stabilize CO2 concentrations at 1990 levels, given world population in that year. As the chart makes clear, this "atmosphere-stabilizing" average per capita emission is inversely related to world population: As population rises, the atmosphere-stabilizing emission falls, restricting further the sustainable use of fossil fuels on an individual basis. The data on which the ranking is based are presented more fully in Appendix 2 in a more comprehensive listing that includes 33 less populous nations.

The study begins with a brief overview of the human influence on climate change. It then considers recent examinations of population’s role in the growth of CO2 emissions before describing the model of atmospheric CO2 stabilization and exploring its implications. A final chapter examines how population policies can contribute to efforts to slow climate change, efforts which must also sharply curb per capita consumption of fossil fuel and other resources if they are to succeed. The methodology used in the study is outlined in Appendix 1.

The goal of stabilizing greenhouse gas concentrations may appear exceedingly ambitious given today’s gingerly efforts merely to stabilize emissions by the end of this decade. The analysis presented here, however, illustrates an important set of population-environment linkages. The issue of population growth is central, in a tight embrace with consumption of fossil fuels and other resources, to efforts to sustain human activities in an envelope of air that can neither be expanded nor replaced.


2. Elisabeth S. Vrba. 1993. "The Pulse that Produced Us." Natural History, May; "Climate and the Rise of Man." U.S. News & World Report. 1992. June 8.

3. Stephen C. McCaffrey. 1993. "Water, Politics and International Law," in Water in Crisis: A Guide to the World’s Fresh Water Resources. Peter H. Gleick, ed. Oxford: Oxford University Press.

4. J. T. Houghton, G. J. Jenkins, J. J. Ephraums. 1993. Climate Change: The IPCC Scientific Assessment. Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press.

Formatted for the web by:

Committee for the National Institute for the Environment
1725 K Street, NW, Suite 212, Washington, D.C. 20006-1401

Phone (202) 530- 5810 [email protected].org Fax (202) 628-4311