Global Climate Change and Population
Growth: Two Challenges in One

Around the world, people in many walks of life—scientists, government officials, business and political leaders, individual citizens—are increasingly focusing on halting global climate change and population growth. In fact, these twin challenges are in some important ways one and the same challenge.

Since 1950, the number of people in the world has surged from 2.5 billion to more than 6.2 billion. At the same time, carbon dioxide and other gases in the atmosphere have risen as people use more fossil fuel, produce more chemicals, and cut down more forests. As a result, average global temperature has climbed. The 1990s were the warmest decade in the 20th century; 1998, 2001 and 2005 were the hottest years on record. There is wide agreement that this will accelerate if current trends persist and that warming will continue for many years even after greenhouse gas concentrations peak.

Global warming’s projected impact on human beings is serious. Rising sea levels increase coastal flooding and erosion and pollute groundwater supplies. Higher average temperature reduces coastal cropland and living space. More destructive and more frequent hazardous weather is likely. A warming climate also threatens public health. It produces longer, more intense heat waves. Changing rain and snow patterns significantly increase the populations of regions under extreme water stress. Warming and population growth together can produce shortages that lead to the exploitation of sensitive areas like hillsides, flood plains, coastal areas, and wetlands. These conditions may also produce large numbers of international environmental refugees. Their migration in turn challenges existing social, economic, and political structures.

Human population growth and climate change are critically linked. First, the size of the population and its activities will be major factors in the extent of warming. Consider the big difference between the low projection of the United Nations for a population cresting at 7.9 billion in 2050 and its high projection of an increase to 10.9 billion in 2050 with continued rapid growth thereafter. How this actually turns out in the next 50 years—whether the population is bigger but level or even bigger and growing—depends on fertility and mortality trends and access to reproductive health services and education, particularly in the developing world. It will in any case have great impact on the extent of global warming and its consequences for society, the economy, and the environment. Second, population size will very much determine the effects on that population of climate change. Greater human numbers may limit the ways societies can respond or adapt to a rise in sea level, changes in precipitation patterns, and other products of warming.

If ratified, the 1997 Kyoto international agreement on climate change commits 38 industrialized countries to cut national emissions of greenhouse gases by an average 5.2 percent between 1990 and 2010. Developing nations would face no specific limits on emissions because developed countries have mostly caused the problem and are obliged under the agreement to take the first steps.

It’s important here to distinguish between per capita emissions and national emissions. On a per capita basis, global carbon dioxide emissions have been relatively flat in the last 30 years even though the total rise in carbon dioxide emissions around the world closely matched population growth. But global per capita figures mask huge gaps in per capita emissions country by country. That’s because the average person in the United States in 1998, for example, contributed five times the emissions of the average Mexican and 19 times as much as the average Indian. Put another way, the 20 percent of the world’s population living in countries with the highest per capita emissions in 1995 contributed 63 percent of the world’s fossil-fuel emissions.

By contrast, national emissions are those that take place within a country’s borders. They reflect the country’s size as much as the use of fossil fuels by each inhabitant. China thus appears as a major source of climate change, even though seven people in China contribute less carbon dioxide on average than one American. But this does not leave developing countries free to do nothing about their emissions until developed countries tackle their own. That would only perpetuate the disparities.

Though emissions in developing regions of the world are far lower on a per capita basis, the gap is narrowing. Any future global climate change agreement will clearly have to take account of population growth and decline, international migration, and changing levels of per capita emissions in developing and developed countries. Kyoto is an important first step.

International cooperation on population has meanwhile gone a long way to slow the growth of world population. But fertility rates in many countries remain high. A quarter century of research shows that those rates decline when voluntary family planning is universally available and educational opportunities for girls and economic opportunities for women increase. Indeed, long-range strategies to address the threat of climate change are unlikely to succeed without paying careful attention to demographic trends.

In the end, effective climate protection will require developing countries to study all these factors as the basis for their required participation in agreements to limit emissions.

Scientists across the globe agree that the influence of humans and their activities on the earth’s atmosphere and climate is an established fact. If population growth and climate change are closely linked, then they should be integrated into policy and challenged together. Long-term strategies to reduce global greenhouse gas emissions in an equitable manner will need to account for the current broad differences among nations in per capita emissions. Effective, voluntary family planning plus improved educational and economic opportunities for girls and women are a central part of good population policy as well as a key to greenhouse gas reduction.

Actions taken now will bring closer the day when population and atmospheric changes are neither rapid nor threatening. With sound population policies and new technologies of energy production and consumption, governments can make the reversal of world population and emissions growth by the middle of the next century more likely.