UNFPA - United Nations Population Fund

State of World Population 2009

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2  At the brink

The first order of business in dealing with human-induced climate change is to stop making it worse.

A hotel in Taiwan Province of China toppled into the sea after Typhoon Morakot lashed the shoreline in August 2009.
© Associated Press

Actions now to reduce greenhouse-gas emissions in the future will help humanity avert disaster in the long run.

There is no time for delay; we are already at the precipice. The Intergovernmental Panel on Climate Change concluded in 2007 that even current concentrations of greenhouse gases could send temperatures past a 2-degree cumulative increase above the earth's average temperature before the Industrial Revolution began.(1) Based on assessments by the Panel and others of the probable impacts of various increases in global temperatures, many Governments and non-governmental organizations have accepted this 2-degree mark as the upper limit that should be respected to avoid potentially catastrophic human-caused climate change.(2)

The large volume of greenhouse gases already put into the atmosphere by human activity since the Industrial Revolution—but especially in the past 40 years—has given climate change so much momentum that only a concerted, comprehensive push by all nations and people stands a chance of slowing down or reversing the warming of the earth's surface.

All nations and all human beings have contributed in varying amounts to the atmosphere's heat-trapping burden, not just through emissions of carbon-dioxide from burning fossil fuels, but also through carbon dioxide related to land-use changes, from methane (more than half of it rising from farm fields), from nitrous oxide (more than four-fifths of these emissions are from agriculture), and from every other gas whose molecules hold more than two atoms together.(3)

From 1850 to 2002, countries we now call developed accounted for an estimated 76 per cent of cumulative carbon-dioxide emissions from fossil-fuel combustion, while the countries we now call developing accounted for an estimated 24 per cent, according to the World Resources Institute. The Institute's analysis of cumulative emissions, however, does not take into account emissions related to land-use changes or recent deforestation, much of which occurred in developing countries. Boosted by growing populations and rising affluence, the sum total of all developing countries' emissions began exceeding the totals of all those of developed countries in 2005 and now make up 54 per cent of the total, according to the Intergovernmental Panel on Climate Change. In 2007, China is believed to have overtaken the United States in total carbon-dioxide emissions resulting from fossil-fuel combustion.(4)

While developed countries contributed the majority of the increment in fossil-fuel carbon dioxide that has accumulated in the atmosphere since the Industrial Revolution began, the International Energy Agency projects that developing countries will account for the majority of the growth in total volume of carbon-dioxide emissions related to fossil fuels from 2008 through 2030.(5) With some exceptions, per capita emissions remain generally higher—and in many cases significantly higher—in developed than in developing countries.(6)

Although its role is difficult to quantify amidst the many factors contributing to emissions growth, population growth is among the factors influencing total emissions in industrialized as well as developing countries. Each additional person in a population will consume food and require housing, and ideally most will take advantage of transportation, which consumes energy, and may use fuel to heat homes and have access to electricity. The influence of additional population on increasing emissions is logically greatest where average per capita energy and material consumption levels are highest—that is, in developed countries. And although correlation does not prove causation, the International Energy Agency projects emissions to be lower in 2030 than today only in Europe and Japan, where population is now approaching or already in decline.(7)

The harsh realities of high per capita emissions among industrialized countries and swiftly rising ones among developing countries highlight the urgency of mobilizing all of humanity to stop collectively at the brink of this possible climate disaster zone. Climate scientists such as James Hansen of NASA, the United States National Atmospheric and Space Administration, and researchers at the Potsdam Institute for Climate Impact Research have suggested that the world should aim to stabilize carbon-dioxide concentrations below current levels of more than 380 parts per million. In effect, these scientists are saying, we should retreat from the brink by returning the atmosphere to the same state it was in around 1990.(8) A critical question for climate negotiators, Governments and the people of all countries is how responsibility for achieving such a retreat will be equitably allocated in a world in which some populations have contributed disproportionately more to climate change.

Population change and emissions

The climate-science community generally points to the changing size and the pace and structure of population growth as integral to understanding climate change. This view is reflected in the Intergovernmental Panel on Climate Change's 2007 Fourth Assessment Report, which states that "gross domestic product per capita and population growth were the main drivers of the increase in global emissions during the last three decades of the 20th century."(9)

Research published by the International Energy Agency in 2006 tracked four major factors contributing to greenhouse-gas emissions from 1970 through 2000 and projected how these same four factors might lead to more or fewer emissions between 2000 and 2030. The research showed that rising per capita incomes have been and will be responsible for the largest share of emissions. Improvements in "energy intensity"—the amount of energy needed to generate a given amount of economic product—is accounting for a larger reduction in greenhouse-gas emissions over time. Meanwhile, population growth has been a smaller but consistent contributor to growth in energy-related carbon-dioxide emissions.(10)

Climate negotiators are beginning to raise population issues as part of the process leading to a new climate agreement in Copenhagen in December 2009. No Government or United Nations entity is suggesting to "control" population. Indeed, fear of appearing supportive of population control has until recently held back any mention of "population" in the climate debate. Nonetheless, some participants in the debate are tentatively suggesting the need at least to consider the impacts of population growth. The European Union has tabled a proposal that population trends be among the factors that should be taken into consideration when setting greenhouse-gas mitigation targets. The other factors are gross domestic product per capita, the "greenhouse-gas intensity" of countries' gross domestic product and past emission trends.(11)

Greenhouse-gas intensity reflects how a specific amount of greenhouse gases, measured in a uniform way based on each gas' warming potential relative to carbon dioxide, is emitted with each currency unit (such as a dollar or euro) of economic activity. So if global greenhouse-gas intensity declines fast enough, the global economy can grow even while emissions shrink—the principal objective of climate policy, since most decision makers want economic growth but also want to reduce greenhouse-gas emissions. Some argue that patterns and levels of consumption are a more important influence on climate change than population growth. In the early 1990s, when a debate on this question was especially active among some researchers in both industrialized and developing countries, environment and development specialist Atiq Rahman of Bangladesh noted what he called the "extreme disparity" in per capita emissions and labelled consumption, rather than population, the "climate bomb." "Climate change is far more sensitive to consumption patterns than to demographic considerations," Rahman wrote, since "demographic dynamics are subject to greater inertial forces than consumption and production patterns.... [T]ackling consumption not only has sounder ethical foundations, but it also has greater scope for rapid action."(12)

The defense of consumption as the main arena for action on emissions reduction has faded little in the last two decades, perhaps in part because it shifts most of the blame for climate change to wealthier countries with patterns of higher consumption. "[T]he world's richest half-billion people—that's about 7 per cent of the global population—are responsible for 50 per cent of the world's carbon dioxide emissions," wrote environmental journalist Fred Pearce in 2009. "Meanwhile, the poorest 50 per cent are responsible for just 7 per cent of emissions."(13)

Still, calculations of the contribution of population growth to emissions growth globally produce a consistent finding that most of past population growth has been responsible for between 40 per cent and 60 per cent of emissions growth. Indian researchers Jyoti Parikh and J. P. Painuly noted during the early 1990s debate mentioned above that falling birthrates in the 1990s "could mean significant reductions in greenhouse-gas emissions [over what would otherwise occur] by 2100." Each birth results not only in the emissions attributable to that person in his or her lifetime, but also the emissions of all his or her descendents. Hence, the emissions savings from intended or planned births multiply with time. One reason for this assessment of population growth and greenhouse-gas emissions is the large influence of population increases on total emissions in some developed countries. In the United States, for example, per capita emissions of fossil fuel-generated carbon dioxide remained essentially unchanged even during the generally economically healthy years from 1990 to 2004. For the United States as a whole, the country's total emissions rose in parallel with its population, at 18 per cent a year. This relationship varied, however, across each of the country's 50 states. In some states, per capita emissions went down as populations rose, and vice versa.

Zimbabwean farmer Mabel Zevezanayi holds a dried corn cob in Bikita District, affected by drought.
© AFP/Getty Images

In 1991, physicist John P. Holdren, now chief science advisor to U.S. President Barack Obama, noted that "changes in settlement patterns necessitated by population growth result in more transport, per person, of resources, goods, and people," making a case that population growth directly stimulates consumption growth. Other increases in energy consumption, he suggested, might result in more use of air conditioning if densely populated urban areas create "heat islands" or "if population density and distribution create demands for energy-intensive services not required when population was smaller."(14)

The effect Holdren identified now challenges some efforts in the United States to shift to renewable energy. By one estimate, a given amount of renewable energy may require 300 times as much land as the same energy produced by fossil fuels. The reason for this is that the extraction of fossil fuels generally requires only a limited amount of land, where mines or drilling wells transfer them from the earth's crust to the surface. Solar power, by contrast, is based on large areas of photovoltaic cells or mirrors capturing and concentrating the power of sunlight over large land areas. Wind power generally requires large fields on which many giant turbines may be placed. Environmentalists and U.S. Government officials alike worry the land hunger of renewable energy projects will add to already stiff competition between human and ecosystem needs, especially in the western United States.(15)

The approach to population dynamics endorsed in the Programme of Action of the International Conference on Population and Development (ICPD) for developing countries—respecting reproductive rights and providing universal access to sexual and reproductive health services, including voluntary family planning—is appropriate to developed countries as well. Rates of unintended pregnancies are actually higher in the industrialized countries than in the developing ones, according to the Guttmacher Institute, which studies the phenomenon in both blocs. In Europe, Australia, Canada, Japan, New Zealand and the United States, an average of 41 per cent of all pregnancies are unintended.(16) In the developing countries, an estimated 35 per cent of pregnancies are unintended. Preventing unintended pregnancies could contribute to population stabilization in the long run and may in turn contribute to a reduction in greenhouse-gas emissions in the future.(17)

[12] Population growth scenarios

The Population Division of the United Nations Department of Economic and Social Affairs has projected various scenarios for world population size in 2050, based on a variety of assumptions about fertility rates and other factors that influence growth. In the "low-variant" scenario, for example, nearly 8 billion people will inhabit the earth by 2050. This scenario assumes a fertility rate of 1.54, well under the 2.1 "replacement fertility" rate. Total fertility worldwide today is 2.56.

In its medium-variant scenario, the Population Division projects fertility in the less-developed regions as a whole to drop from 2.73 children per woman in 2005-2010 to 2.05 in 2045-2050. To achieve such reductions, the Population Division states, it is essential that access to voluntary family planning expands, particularly in the least developed countries. Around 2005, the use of modern contraceptive methods in the least developed countries was 24 per cent among women of reproductive age who were married or in a union. Another 23 per cent of such women were not using contraception, despite a wish not to become pregnant now or within the next two years—the definition of "unmet need."(18)  According to the United Nations Secretary-General, in a report on world population and the ICPD Programme of Action, there are an estimated 106 million married women in developing countries who have an unmet need for family planning.(19)

World population scenarios, 2050
Low Medium High
7.959 billion 9.150 billion 10.461 billion
World fertility rates, 2045 to 2050, by population growth scenario
Low Medium High
1.54 2.02 2.51

Population and climate change: a closer look

A report of the Secretary-General to the United Nations Commission on Population and Development's 42nd session in early 2009 takes a more nuanced view of the relationship between population, development, greenhouse-gas emissions and climate change. The report, prepared by the Population Division, linked the rapid growth of world population in the 20th century with even more rapid growth of urban population, production, land in cultivation, water use and energy consumption. "Together," the report suggested, these trends "are having unprecedented impacts on the environment, causing climate change, land degradation and loss of biodiversity."

The influence of population growth on emissions, however, is complicated by the other forces. According to the Population Division, "The relation between population growth and increasing greenhouse-gas emissions is not straightforward, and the scenarios of future emission trends do not permit assessing the effects of population dynamics net of economic and technological changes. Furthermore, changing population age structures, increasing urbanization and changes in household size interact in affecting emissions."(20)

Researchers began dissecting the impacts of population change on emissions only in the mid-1990s. Among the early findings was one in 1995 that reductions in household size, which often accompany lower fertility and higher economic growth, could significantly increase total greenhouse-gas emissions. These researchers found that homes are basic units of energy consumption and tend to be heated or cooled whether occupied by a family of seven or by a single person. Indeed, so strongly did the reduction in household size appear to boost emissions that demographers in the International Institute of Applied Systems Analysis' World Population Program stated, "A divorce may cause more carbon dioxide emissions than an additional birth."(21)

The importance of smaller households in elevating emissions, affirmed by a 2004 study quantifying such impacts, underlines the fact that population growth occurs in specific contexts that can enhance or dampen its influence on the environment.(22) Even the demographic unit—an individual or household, for example—might significantly alter the outcome of emissions models. The effect of smaller households on emissions led some researchers to speculate that population ageing, the increase in the average age of a population as life expectancy increases and fertility declines, might lead to rising emissions—at least partially offsetting emissions savings resulting from the slowdown in growth itself. Studies of ageing itself have, however, produced conflicting findings. A group of researchers associated with United States and European research institutions found ageing to reduce emissions significantly in the United States and somewhat less significantly in India and China.(23) Although older people are likely to live in smaller households than younger people, the researchers found, the impact will be more than offset by the slower economic growth and reduced consumption presumed to accompany an ageing population.

Urbanization works in the opposite direction, some of these same researchers found. A shift of population from rural areas to cities appears likely to boost emissions substantially. This is not necessarily because people who live in cities contribute more on a per capita basis to greenhouse-gas emissions than those who live in rural areas. Other researchers, however, have argued that this is a myth and that urban areas now contribute much less than half the world's greenhouse-gas emissions despite being home to more than half the world's people.(24) The economic growth stimulated in cities tends to have a ripple effect throughout a country, helping boost economic growth in rural areas as well. In turn, greater economic growth may therefore boost greenhouse-gas emissions throughout a whole country.(25) In general, economic change continually reveals itself as the more immediate influence on greenhouse-gas emissions than population change.

[13] Women, men and greenhouse-gas emissions

If greenhouse-gas emissions begin with individual human activities, might those of women somehow be different from those of men? There is little research that aims to answer this question, particularly in developing countries. And in the developed countries, there have been only a handful of public opinion surveys on climate change or other environmental issues that disaggregate results by sex.

According to research published by the Organization for Economic Cooperation and Development in 2008, women in industrialized countries are more likely to be "sustainable consumers," meaning, for example, that they tend to buy ecologically friendly and organic foods, are more likely to recycle and are more interested in efficient energy use. Women in these countries account for as much as 80 per cent of consumer decisions, the research shows.(26)

It is unclear, however, whether consumption patterns that contribute less to the warming of the atmosphere are the result of women's environmentally conscious decisions at the household level or the result of chronic economic and social inequalities that prevent women from benefiting from and contributing to their countries' and communities' development. Several gender-specific studies of attitudes about the environment or climate change in the United States generally support the view that women are more likely than men to buy "green" products, which are advertised as less detrimental to the environment. Women were also generally less likely than men to trust Governments and corporations to solve environmental problems and somewhat more likely to want to take action personally on them. These gender-based differences were more pronounced at higher incomes.(27) In one study conducted in 22 countries, researchers found women were somewhat more likely to care about environmental problems such as climate change and to change their behaviour as a result.(28)

In Sydney, Australia, a 2008 survey of suburban residents about environmental sustainability found women and girls easier to attract to cooperative initiatives, more socially focused, and more concerned about the impacts of climate change. Men and boys were less likely to get involved in sustainability and more drawn to technology, governance issues and business in discussing environmental issues.(29)

Nordic researchers have probed the implications of differences in emissions and found women in developed—and developing—countries to have less impact on the atmosphere overall. The chief reason seems to be that the two sexes move differently from place to place, with men more likely than women to drive a car (75 per cent more likely in Sweden(30)) and to fly in airplanes. This difference, however, appears to stem more from unequal access to economic resources and less influence over decision-making than from behaviour or attitudes regarding the environment or transportation generally. The study also quantified another differential in greenhouse-gas-related consumption: men in developed countries eat more meat—139 grams daily in Denmark on average, compared to 81 grams for Danish women. Not only do women eat less in proportion to their body size, but at least in some countries they consume a more vegetable-oriented and less meat-based diet.

Population and future emissions

No human is genuinely "carbon neutral," especially when all greenhouse gases are figured into the equation. Therefore, everyone is part of the problem, so everyone must be part of the solution in some way. The world's Governments and peoples will need to work together on every aspect of the factors that increase greenhouse-gas emissions. One such factor is the earth's growing population.

A woman works in her cornfield near a coking factory in Changzhi, Shanxi Province, China.
© Reuters

If the United Nations Population Division's low population growth scenario—about 8 billion people by the year 2050—materializes, it might result in 1 billion to 2 billion fewer tons of carbon emissions than if the medium-growth scenario—a little more than 9 billion people by 2050—materializes, according to climate scientist Brian O'Neill of the National Center for Atmospheric Research.(31) Others have estimated comparable emissions savings by 2050 through the application of known energy-efficiency techniques in all new buildings worldwide or by erecting 2 million 1-megawatt wind turbines to displace coal-fired power plants currently in use.(32) Moreover, the annual emissions savings would continue to grow substantially after the middle of the century as world population peaked and began declining, compared to continued population growth assumed in the medium-growth projection. This means that the net emissions savings achieved through a low population growth scenario would be equivalent to the net emissions savings achieved through major investments in energy technologies in a medium population growth scenario.

British economist Nicholas Stern estimated that in order to keep global temperatures from crossing into a potentially catastrophic zone, "global average per capita [greenhouse-gas] emissions...will—as a matter of basic arithmetic—need to be around two tons by 2050," assuming a world population of 9 billion people and speaking in terms of carbon dioxide equivalents. "This figure is so low that there is little scope for any large group to depart significantly above or below it."(33)

If the world followed the trajectory of the United Nations Population Division's low-variant projection of 8 billion people, the earth's atmosphere would be able to tolerate higher per-capita emissions, since fewer people would be emitting greenhouse gases.(34) The low-variant projection assumes lower fertility rates that might result from increased access to reproductive-health services, including family planning, and other actions to increase opportunities and freedoms for women and girls. One study of the cost of averting a fixed amount of fossil-fuel carbon-dioxide emissions found that dollar-for-dollar, investments in voluntary family planning and girls' education would also in the long run reduce greenhouse-gas emissions at least as much as the same investments in nuclear or wind energy.(35)

© Amanda Koster/Corbis

According to a 1992 report by a committee of the United States National Academy of Sciences, "family planning impacts on greenhouse-gas emissions are important at all levels of development." The committee concluded, "The reduced population growth associated with higher income growth...offsets in large part the higher greenhouse-gas emissions associated with faster economic growth. The family planning effects indicate that, as of 2020, carbon emissions will be about 15 per cent lower for the lower-, middle- and upper-middle-income countries than they would be without family planning. Strong family planning programmes are in the interests of all countries for greenhouse-gas concerns as well as for broader welfare concerns."(36)

Investing in women and girls in ways that improve their health, well-being and status in their societies leads to reductions in fertility rates and will thus contribute to a reduction in greenhouse-gas emissions in the long run.

Women and emissions reduction

There may be opportunities to tailor efforts to reduce emissions and to pull carbon out of the atmosphere more effectively by considering gender differences in any discussion about consumption.

Women produce roughly half the world's food, according to the Food and Agriculture Organization of the United Nations, and anywhere from 60 per cent to 80 per cent of food in most developing countries.(37) Natural land-based carbon sequestration—the potential of farm and forest soils, trees, perennial crops and other plants to absorb carbon and keep it out of the atmosphere for decades—is attracting increasing interest as every possibility for holding down greenhouse-gas concentrations is pursued. If financial instruments could be devised to encourage such practices—as seems likely to occur as climate change impacts become more obvious and damaging—women farmers could be at the forefront of mitigation efforts.(38) This could have a substantial impact on women's livelihoods as well, assuming laws are restructured and cultural norms shift as needed in some countries so that women can own the land they farm and control the income they earn.

Already, the world has witnessed the power of women to take actions that contribute to lower levels of atmospheric carbon dioxide. Wangari Maathai won the Nobel Peace Prize for a lifetime of environmental activism that began by mobilizing women to plant tens of thousands of trees in deforested and degraded soils of Kenya. In India, the Chipko movement drew women, the original "tree huggers," as early as the 1970s to protect forests and their own forestry rights by linking hands and arms around trees to dissuade the loggers assigned to fell them. The movement led to major reforms in Indian forestry laws that resulted in greater forest cover today (and hence more carbon in trees and less in the atmosphere) than would otherwise be the case. One study of deforestation, an activity performed overwhelmingly by men and responsible for a substantial proportion of all carbon-dioxide  emissions, found that a high presence of women's non-governmental organizations in low-income countries may help protect forests against destruction.(39)

[14] Women and reforestation

The relative dearth of research on gender aspects of deforestation is surprising, given the strong connection between fuelwood and activities such as cooking and the firing of ceramics. Research shows that in many developing countries, women must walk farther and farther to gather fuel. In one rural community in Sudan, for example, the time required quadrupled over a single decade. Moreover, the livelihoods of women in rural areas often depend on forest resources. Loss of forests may therefore undermine income-earning opportunities. Finally, loss of forests often affects women's health: carrying heavy loads of fuelwood over long distances can result in spinal damage, complicate pregnancies and increase the risk of maternal mortality.

In recent decades, however, such women-focused non-governmental organizations as the Green Belt Movement in Kenya and the Women's Environment and Development Organization in the United States have mobilized to protect and even expand forested lands. Many such groups also advocate for or help ensure compliance with environmental treaties.

Sociologists at three United States universities—the State University of New York at Stony Brook, Brown, and Clark—recently examined deforestation in 61 nations between 1990 and 2005 and found that countries with large or numerous women's and environmental non-governmental organizations showed significantly lower levels of forest loss. The researchers suggested that women's non-governmental organizations achieved what theory might predict: they advocated successfully for forest protection and mobilized activity that had a net positive effect on forest conservation.(40)

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