SUMMARY: New Data on a Critical Linkage
Some years bring the highest temperatures the world has experienced in several centuries, and 1998 was one such year. But every year sets a record on at least two other fronts: The atmosphere has higher concentrations of carbon dioxide and other globe-warming greenhouse gases, and the planet has more human beings. This report highlights the neglected linkage of population and climate, and illustrates the contribution that sound population policies could make to international efforts to slow climate change.
A global effort to make energy use as efficient as possible and to effect a transition from carbon-based to carbon-free fuels is essential to slowing global climate change. Such an effort, the objective of current negotiations on climate change, is much more likely to have enduring success if world population grows more slowly and eventually stops growing. Today, the most rapid population growth tends to occur in countries where per capita greenhouse emissions are relatively low. Yet economic development is likely to boost these nations’ per capita emissions at a time when their total populations will be much higher than currently. Future rates of population growth, however, are anything but certain. They depend critically on decisions the world’s governments make today.
In the past few years, data sets have become available that track annual changes, country by country, in population and in atmospheric emissions of carbon dioxide (CO2) from the combustion of fossil fuels and the manufacture of cement. Combining these two data sets yields a third body of data: country profiles of per capita CO2 emissions from 1950 to 1995, which could prove useful in international negotiations on human-induced climate change. During these 45 years, the world’s population grew from 2.5 billion to 5.7 billion human beings. By 2040, after 45 more years, United Nations demographers project world population will have gained between 2.1 billion and 4.4 billion more people. Just as past population increase has influenced the composition of the earth’s atmosphere in the late 20th century, the rate of future increase will influence the earth’s climate for centuries to come.
This publication, an update to the 1994 Population Action International (PAI) report Stabilizing the Atmosphere: Population, Consumption and Greenhouse Gases,1 profiles per capita emissions of CO2 derived from fossil fuel combustion and cement production in 181 countries. It also includes a graphical ranking of countries with populations greater than one million by their 1995 per capita emissions, as well as information and charts on related population and emissions trends. The data highlight the significant global disparities in individual human use of the atmosphere for the disposal of CO2, the single most important driver of human-induced global warming.2
These disparities in global emissions complicate international efforts to address climate change, since responsibility for the problem varies so broadly. They also cloud the role of population growth in changing climate, since the greatest per capita contributions to climate change are made by populations, such as those of the United States and Europe, that are growing relatively slowly. Most rapidly growing populations, by contrast, have very low per capita greenhouse gas emissions. Per capita emissions and populations are nonetheless increasing rapidly and in tandem in much of the world. This growth of both population and per capita emissions occurred in industrialized countries many decades ago, and their combined population of roughly 1.2 billion today helps explain the disproportionate impacts of their high consumption on the atmosphere. An even greater multiplication of forces will complicate efforts to stabilize the atmosphere in the next century, as economic development proceeds and the population of developing nations approaches 6 billion or more.
Several conclusions emerge from a consideration of data on population with data on carbon dioxide emissions:
- No long-term approach to restraining greenhouse gas emissions is likely to succeed without addressing fairly the inequities of per capita emissions. The atmosphere is the common property of all human beings, and the impacts of human-induced climate change will ignore national borders. To win global support, future climate agreements will need to recognize that the limited capacity of the atmosphere and biosphere to absorb greenhouse gas emissions, without adding to the risk of climate change, must be shared fairly on a per capita basis. This need not require international convergence on very low individual emissions. A flexible system of emissions permits tradable among all nations would provide some latitude for those with higher emissions to compensate those with lower emissions, while still encouraging reductions in the global total.3
- The importance of population dynamics to climate change becomes clear if negotiators consider the long-term need to stabilize atmosphere and climate while allocating emissions rights equitably among all human beings. Negotiators and the legislators who ratify climate agreements will need somehow to bridge the gap between what is possible politically with what is necessary environmentally, and to do so in ways that are fair to the populations of all countries. World population will likely grow even as global greenhouse emissions decline. The more slowly population growth proceeds, the more rapidly global emissions are likely to decline, and this will be especially true if equity is a central component of strategies aimed at slowing climate change. For population size determines the levels of greenhouse gas emissions on a per capita basis that will sustain a stabilized atmosphere and thus a climate relatively unperturbed by human activities.
- The more ambitiously future climate agreements seek to restrain greenhouse gas emissions and the further one looks into the future, the more important slowing population growth will become. This is illustrated by a chart of the per capita emissions that would be needed to stabilize atmospheric CO2 concentrations at 450 parts per million by volume (ppmv), compared to approximately 360 ppmv today, under all three of the principle United Nations long-term population projections to 2150.
Achieving the United Nations low projection of population growth through the year 21504 would help make possible a global CO2 emissions trajectory that trades increased emissions in the near future for sharp declines after the year 2010. The atmosphere’s carbon dioxide concentrations would stabilize at something less than the often-projected doubling from pre-industrial times. Individuals could actually begin emitting increasing amounts of CO2 into the atmosphere by the end of the 21st century, commensurate with the modest decline of global population at that time, without contributing to the risk of additional climate change.
Beyond the numbers, climate negotiators and policymakers can take encouragement from the relatively clear path to slower population growth that other negotiators have already laid out. Making basic health services like family planning universally available, while improving access to education for girls and economic opportunities for women, could bring about the UN’s low population projection. The cost would be modest when compared to the spending that will be required to shift the global economy away from its current dependence on petroleum, coal and natural gas. That shift is essential no matter where world population heads. The point is simply that sound population and energy policies can and should work together to preserve a global climate in which humans and nature can thrive.
The earth’s atmosphere and biosphere can absorb moderate emissions of greenhouse gases without significantly altering the atmosphere and influencing climate. Only in historically recent times has humanity exceeded these “climate-safe” emissions levels. Now emissions must come down again to levels the atmosphere and biosphere can absorb. The size of the world’s population ultimately determines the size of per capita emissions of greenhouse gases that are compatible with a global climate unperturbed by human influences. Only a world population that never doubles again is likely to allow modest use of fossil fuels without continuous greenhouse gas buildup in the atmosphere. Future generations have an immense stake in decisions about population policy that are made today.
- Robert Engelman, Stabilizing the Atmosphere: Population, Consumption and Greenhouse Gases (Washington, DC: Population Action International, 1994).
- Per capita emissions only approximate the emissions for which each individual is responsible. Income disparities and other major differences within nations are reflected in comparable individual emissions disparities. Lacking significant data on differences in emissions within nations, however, per capita carbon dioxide data by nation affords the best available picture of global differences in emissions.
- Most current discussions of tradable emissions permits refer to trades only between industrialized countries. For a fuller discussion of the concept of tradable emissions permits, see Stabilizing the Atmosphere.
- United Nations Population Division, World Population Projections to 2150 (New York: The United Nations, 1998).