Debating the link between emissions and population

Is population an important variable in carbon emissions? Sure. But it's far from the only variable and by no means does it determine carbon emissions.

Take China, a country where growth trends for population and emissions have diverged widely in recent decades. China's population growth has slowed markedly since the early 1980s, when Beijing began enforcing a strict one-child policy. Average annual population growth was 1.25 percent between 1987 and 2000, but between 2000 and 2014 it was only 0.56 percent—half as high in the later period as in the earlier period. But carbon emissions tell a different story. Between 1987 and 2000, annual growth in carbon dioxide emissions was 4.75 percent. Between 2000 and 2014, the annual rate of growth increased to 12.7 percent—well over twice as high in the later period as in the earlier one.

This is all consistent with an equation known as the Kaya identity, which states that carbon dioxide emissions are the product of four factors. Human population is one of these factors. The other three are gross domestic product per capita; energy intensity (the amount of energy used per unit of gross domestic product); and carbon intensity (the amount of carbon dioxide produced per unit of energy used). The "other three" factors can ultimately be summarized in one number—emissions per capita—a number that can decline when people's behavior changes and nations achieve social progress. Social progress and economic growth can, as demonstrated by experiences in East Asia, Western Europe, and North America, reduce population growth rates. So the best way to limit carbon dioxide emissions is through altering behavior—not through limiting population.

Management and governance. Carbon dioxide emissions are a kind of pollution, but people nonetheless have a right to emit carbon dioxide as they go about their lives. Unfortunately, individual people have strong incentives to produce more carbon pollution than is in everyone's collective interest—that is, the "tragedy of the commons" comes into play. Lowering carbon dioxide emissions per capita, then, requires good management of people's emissions behavior, which in turn requires that low-carbon infrastructure and good carbon governance be established.

Low-carbon infrastructure includes, in addition to public transportation systems such as subways and high-speed railways, low-carbon energy generation systems such as wind and solar farms and electricity grids that link customers with low-carbon energy. In recent years, much of this has been established in Sichuan province, the area in southwestern China where I was born. For many centuries the farming families in Sichuan had burned biomass for cooking—but in the early 1990s, Sichuanese people began purchasing coal to burn in their stoves. Sichuan's coal, unfortunately, is generally of lower quality than the coal produced in most other Chinese provinces—its sulfur content is higher and its heating value is lower. In March 2014, however, drilling began at the giant Longwangmiao natural gas field in southern Sichuan. A pipeline soon began to transport gas from the field to nearby cities, towns, and villages. Natural gas is more expensive than coal or biomass, but farmers enthusiastically embraced natural gas for cooking because natural gas is cleaner and gas stoves make it very easy to adjust the flame—a very important issue in Sichuanese cuisine. The gas pipeline and other infrastructure elements have helped bring about an energy revolution for Sichuan's farming families—a revolution that, because natural gas entails much lower carbon dioxide emissions than coal, reduces emissions per capita.

But for climate mitigation, establishing good governance is as important as improving infrastructure. Low-carbon infrastructure is of little value if consumers are unable or unwilling to use it. Inconvenience and high costs can undercut the attractiveness of low-carbon infrastructure—if subways and high-speed railway systems are too expensive, for example, customers will shy away from them. Certain entities might even intentionally make it inconvenient to use low-carbon infrastructure. For example, the electricity grids in China are monopolized by two state-owned enterprises—the State Grid Corporation of China and the China Southern Power Grid Company. These companies prefer the stability of coal-fired electricity and other types of thermal electricity to intermittent energy sources such as wind. In China's currently sluggish economic environment, thermal electricity can meet nearly all electricity demand, and the grid companies are intentionally making it difficult to connect wind power to the grid. Under such circumstances it becomes very difficult, if not impossible, for customers to consume green electricity. So even if low-carbon infrastructure is perfect, utilization rates will be low if governance and management are poor.

Reducing emissions per capita depends among other things on supportive tax policy, pricing, and financing. For example, governments can "internalize" the otherwise externalized costs of high-carbon energy sources by levying carbon taxes on coal and oil. By implementing carbon taxes and providing subsidies for renewable energy, governments can support the development of low-carbon energy sources such as hydrogen-based power and wind and solar energy.

Getting educated. But is it possible to limit or reduce per capita emissions as societies get richer? Certainly, rich people are able to consume more of everything, including high-carbon energy. On the other hand, the recently concluded Paris climate agreement, in its requirement that developed countries provide developing countries with $100 billion a year for climate mitigation and adaptation, incorporates the idea that poor countries will be able to reduce their carbon emissions if they have more money on hand. But in today's China, a real threat exists that carbon dioxide emissions will increase because of poverty. China's economic growth is slowing. Many Chinese people are increasingly unable to pay extra for low-carbon energy and local governments are increasingly unable to subsidize such energy. Indeed, some government entities and poor consumers are returning to cheap, high-carbon energy sources such as coal. The weakening economy is harming air quality in China and also reducing ambitions for climate mitigation. The jury is still out on how economic fortunes will influence carbon emissions going forward.

Beyond building low-carbon infrastructure and establishing good governance, one more element is necessary for cutting carbon emissions—improving education, especially for girls. Good education allows people to understand the importance and urgency of reducing carbon emissions. In advanced societies with good education systems, consumption of high-carbon energy may eventually become taboo. Providing good education to girls in particular—again, as experiences in East Asia, Western Europe, and North America demonstrate—will allow women to pursue careers, delay childbearing, and give birth to fewer children. This process will naturally place limits on global human population and, albeit in an indirect way, help reduce carbon dioxide emissions.

There's no single solution for climate change, no magic bullet that can stabilize and eventually reduce the concentration of greenhouse gases in the atmosphere. But separating sex from childbearing represents an underappreciated opportunity to forestall climate disaster.

To be sure, addressing the climate challenge will require a wide range of approaches. Conservation policies must be implemented, and major investments are needed to develop and scale up renewable energy technologies. But another opportunity—often overlooked—is ensuring that every woman has both the information and the means to separate sex from childbearing. All over the world, whenever good family planning programs are put in place, couples choose to have fewer children. The family's health benefits, household resources per capita increase, and each couple's carbon footprint shrinks.

Perhaps the most important equation in the world is one made famous by John Holdren, currently a science and technology advisor to President Obama, and biologist Paul Ehrlich: I=PAT. "I" stands for impact on the environment, "P" for population, "A" for affluence, and "T" for technology. Technology can either ameliorate or intensify human beings' impact on the environment—but affluence and population have a straight multiplying effect. That is, affluence leads to increased consumption and pollution. Higher population means more carbon footprints on the biosphere. But there's a twist: Since per capita emissions in wealthy countries are much greater than in low-income countries, averting an unintended pregnancy in a high-emitting country will do more to help the climate than will averting a similar pregnancy in a low-emitting country.

Though many people acknowledge population's impact on the environment, few go on to mention that population growth is not a fait accompli. In industrialized countries, the average family in the middle of the 19th century had six or more children. Today, families in such countries produce on average about 2.4 children (near replacement level). More recently, in some developing countries, birth rates have fallen remarkably quickly, as in Iran, whose total fertility rate fell from more than five to less than three in just seven years. The fertility rate in Thailand, when voluntary family planning and safe abortion became widely available, fell from six children to 3.5 in 12 years—though it had taken the United States 58 years to make the same transition in the 19th century.

Coercive approaches to population, such as China's one-child policy and forced sterilization in India, should have no part in family planning. But when women are denied the information and means to separate sex from childbearing, pregnancy itself is coercive. So family planning services, from design to implementation, mustn't be about telling couples what to do; the point is giving couples what they want. The good news is that many family planning programs around the world do just that. In particular, they uphold a woman's right to determine how many children she has and when she has them.

For the climate, family planning's potential benefits are profound. A careful study of a voluntary family planning program in California demonstrates that family planning is the single most cost-effective way to abate carbon dioxide emissions. Spending $24 on wind energy averts 1 metric ton of carbon dioxide emissions. So does spending $51 on solar energy. But spending just $7 on family planning achieves the same result.

Lessons of the Sahel. Family planning as a means for mitigating climate change is a familiar enough idea, but family planning for adapting to climate change may sound far out. It is not. Because climate change negatively affects some staple crops, it worsens food insecurity in parts of the world. But according to a 2012 study that modeled climate change, food production, and population growth in Ethiopia, achieving low fertility by 2050 might fully make up for climate change's negative effects on Ethiopian agriculture. (A lower overall population means more calories are available per person.) Perhaps more tellingly, some rural women in Ethiopia say they are choosing smaller families to help them better deal with the negative effects of climate change. Women in Niger say that smaller families mean less competition for food during the lean season.

People concerned with humanity's fate in the face of climate change should pay sharp attention to the words and actions of these women. Niger and Ethiopia are countries of the Sahel, the semi-arid southern border of the Sahara desert. During the 1970s and 1980s, this region suffered massive drought and famine—making the Sahel among the first places on Earth to be ravaged by human-induced climate change. Today, unprecedented population growth and intensifying cycles of drought are undermining the region's food security and development. Yet for every woman in the region who currently uses contraception, three to four others want to space out or limit their childbearing but are not using contraception.

In the poorest countries, the net effect of slower population growth will likely be an increase in carbon emissions—economic conditions will improve and consumption will increase. And that's okay. Meeting women’s contraceptive needs in least-developed, highest-fertility nations is a precursor for development that could help lift nearly 1 billion people out of desperate poverty. On a global level, meanwhile, achieving the medium UN population projection for the end of the century—as opposed to the high projection—would keep more than 7 billion tons of carbon per year out of the atmosphere.

Where the link between population and environment is concerned, too many heads have been buried in the sand. Because of tragic, coercive population programs that have sometimes been enacted in the past, even people who appreciate population's impact on the environment can be afraid to attract criticism by expressing their views. National leaders need to escape this cloud of fear and clearly acknowledge that human beings have exceeded Earth’s carrying capacity. Influential people involved in development, natural resources, and of course climate must recognize that sustainable progress can't be achieved until population is stabilized. Equally important is ensuring international investment, on a level commensurate with the world’s need, in voluntary family planning and in quality education for adolescent girls.

In the wake of the Paris climate conference, many individuals may be wringing their hands—feeling powerless in the face of global climate change. But there is one highly important contribution to the climate that high-consuming couples can make: considering their carbon legacies when they plan their families.

There are those who perceive any effort to limit population growth as "population control." This is a term that chillingly evokes coercive state intervention to control individual reproductive behavior. Population control programs have rarely been implemented without exacting unacceptable ethical costs.

But there's a big difference between coercive state-led population control programs and efforts to slow rapid population growth. Population control programs target the actions of individuals. Efforts to slow the population growth rate, meanwhile, work within existing societal contexts and seek to produce voluntary change.

Population size and composition are among the key drivers of climate change. Whether there are 7 billion or 14 billion people on Earth matters on a fundamental level for the climate. But the relationship between population and planetary health is not straightforward. A child born in, say, North America will have a heavier carbon footprint than will her age-mate born in sub-Saharan Africa.

Regions with the heaviest carbon footprints are experiencing slower population growth than other regions. Many countries—including Japan and Russia, and most nations in Eastern Europe—are experiencing negative population growth. But this is not the case in sub-Saharan Africa. Between 1950 and 2000, the region’s population grew from fewer than 180 million to more than 642 million. Just since 2000, the region’s population has increased by half, to nearly 1 billion. By 2050, the population of sub-Saharan Africa is projected to more than double, to 2.1 billion—and 50 years after that, the region will be home to an estimated 4 billion people. Under that scenario, two out of every five human beings in 2100 will be sub-Saharan Africans.

Sub-Saharan Africa's carbon footprint is light. But the region's rapidly growing population has an environmental impact that is already very evident. Ecosystems such as tropical rain forests are degrading rapidly. Inefficient agricultural practices are creating undesirable land use changes. Biodiversity is diminishing. All these effects can be expected to intensify if Africa's population grows as projected.

African policy makers do care about the region’s rapid rate of population growth—but climate change is by no means the top reason why. In Africa, increased demand for basic services—without increased resources to pay for them—can stretch infrastructures beyond capacity. This makes each successive government in the region appear less effective than the regime that preceded it. Education is a good example of increasing demand for public services. UNESCO estimates that sub-Saharan Africa, to achieve universal primary and lower secondary school coverage by 2030, will require an additional 2.1 million primary school teachers and 2.5 million additional lower secondary school teachers. At the same time, demand for jobs, housing, and other necessities will also increase. Clearly, political leaders in sub-Saharan Africa face enormous challenges due to rapid population growth.

Political leaders are also concerned about population growth because they fear insecurity and instability. Extremists can find adherents more easily in a larger pool—especially in a large pool of young people whose poor education, poor employment prospects, and lack of options can leave them disenchanted.

Leaders also take an interest in population because of the potential for a so-called "demographic dividend"—that is, an improvement in a nation's economic prospects when its ratio of working-age to non–working age people increases.

So it’s no surprise that when African policy makers consider population growth, climate change is not central in their thinking. But what should be the key concern regarding the 4 billion Africans who might exist in 2100?

The issue isn't whether Africa, a continent of more than 3 billion hectares, has enough space for so many people. Even an Africa with 4 billion inhabitants would have far fewer people per unit of habitable land than India has today. Really, the key question is this: What type of people will these 4 billion Africans be? Will they be poor, sick, uneducated Africans trampling over each other to escape? Or will they be healthy, educated, productive Africans delighted to live on the continent of their birth and contributing to regional (and global) progress and development? Most of all, how can sub-Saharan Africa transform its demographic future into something manageable, development-oriented, and economically viable—while fully respecting individual reproductive choices?

African nations can change their demographic and development trajectories for the better if they vigorously pursue three key policy actions. The first is to provide universal access to family planning services, which have been shown to significantly reduce the number of children born even in poor, uneducated, and rural populations. An increase of just 15 percentage points in contraceptive prevalence is associated with a one-child reduction in the number of children born to the average woman. In sub-Saharan Africa, increasing contraceptive prevalence by 45 percentage points could reduce the total fertility rate from 4.7 to 1.7, which would bring the region’s population growth rate to below replacement levels.

The second key policy initiative involves efforts to delay marriage and childbearing. All else being equal, a population in which women begin having children at age 15 will have 25 percent more people after 60 years than a population in which women bear their first child at age 20. The longer a girl's marriage is delayed, the more opportunity she has for personal development—and the better it is for the entire country.

A third important step is to expand girls' access to education beyond the primary-school level. Women, if they receive additional education as girls, have fewer children; this has been demonstrated consistently. Improved education also provides women better opportunities for earning an income—precisely what developing countries need in order to achieve economic development. Implementing these three policy initiatives would lead to more sustainable, more durable, and (most importantly) quicker reductions in the population growth rate than any coercive government action would achieve.

The prospect of 4 billion Africans by 2100 can be cause for concern—or it could inspire commitments to invest in educational opportunities for girls, greater access to family planning, and delayed marriage. These steps would be transformative for the continent. They would generate development and promote economic growth in addition to reducing the demographic burden that contributes to climate change. But while African efforts to slow population growth will contribute to planetary health, one mustn't forget that the greatest culprits in the race to destroy the planet are the countries with the heaviest carbon footprints. Global initiatives and investment are required to support African countries as they work to achieve a demographic dividend—but these must be matched by appropriate, complementary efforts to mitigate the environmental damage wrought by countries expecting zero or even negative population growth.