Trends | Theory | Facts | Food | Environment | Aging | Elderly | Immigration | Urbanization | Family | Women
The association between a rapidly increasing population and the increase in global warming is often made, and when it is presented, most arguments state that a growing population is indeed a threat to global warming. Nancy Birdsall, however, presents a study in which she finds that reducing population growth rates in developing nations will not significantly reduce global warming. Her study relates population growth with gas emissions in several different models, and then follows up with a cost analysis of reducing carbon dioxide emissions through programs aimed at lowering population growth rates. Birdsall’s findings, although they do not concur with more mainstream theories on population growth and global warming, are worthy of a much closer look.
Population growth can contribute to global warming, or greenhouse gas emissions, in several ways. A larger population means an increase in demand for energy for production in industry, for transportation, etc., which in turn mean an increase in fossil fuel emissions. These emissions amount to approximately eighty percent of total carbon emissions. Deforestation is another main cause of global warming. In this case, a larger population means an increased strain on resources (meaning more deforestation) and therefore, more carbon emissions are left in the atmosphere.
Regional differences for both causes of global warming are notable, with developed nations accounting for fifty-five percent of carbon emissions despite having only fifteen percent of the world’s population. In addition, because of their initial lower base, both per capita emissions and population growth are increasing more rapidly in developing nations than in developed nations. Other factors that help distinguish between emissions rates in developing and developed nations include the "emissions intensity" which is higher in developing nations. The emissions intensity refers to the energy increase for each unit of value, and because the shift from agriculture to industry in developing nations requires more drastic increases in energy use, the emissions intensity in these countries is greater. In developed nations, the emissions intensity is decreasing as these countries move from heavy industry to the services sector and the use of cleaner, more environmentally friendly energies. The data in this study shows that even though developing nations currently contribute fewer emissions to the atmosphere, they are a major source in the growth of fossil fuel use because per capita fossil fuel emissions are likely to rise with increasing income. As developing nations continue to have higher rates of population growth, the positive relationship between per capita carbon dioxide emissions from fossil fuels and per capita income will hold. The same is true with the effects of deforestation; however, this rate will not continue to climb indefinitely because of the gradual decrease in the forest base.
In order to study the effects of population growth on fossil fuel emissions, two models were developed to explain population change; the standard scenario and the rapid fertility decline scenario. In the standard scenario, the assumption is made that in countries where fertility is already declining, it will continue to decline at a rate of .6 per five years (the average rate of decline for developing countries in the past). Where fertility rates have not started to decline, it is supposed that the rate will decline to the replacement rate of just over two children per family as life expectancy reaches fifty. In the cases where life expectancy already exceeds fifty years of age, the belief is that a decline in fertility began about 1990. The standard scenario projects that population will grow from 4 billion to about 10.6 billion in the year 2100, despite the assumption that fertility will continue to decline in developing countries. In the rapid fertility decline scenario, life expectancy is not important. Instead, it is assumed that fertility decline began in 1990 and that all developing nations are capable of achieving a rate of decline as quickly as the rates achieved by other nations before them. Population projections are slightly lower, as it is estimated that the population will grow to approximately 8.4 billion by 2100.
How can these projections of population growth and a decline in fertility give us insight into the change in flows of carbon emissions in developing countries? Birdsall outlines a few different methods; the first is from the Intergovernmental Panel on Climate Change (IPCC), the second from the Environmental Protection Agency of the U.S. (EPA), and the third is the Birdsall’s own approach. The IPCC and EPA approaches are derived from the effects of projected future population and income on energy consumption patterns, while taking into account the global energy supply. The result of these studies projects that total emissions from fossil fuels will increase seven-fold. Birdsall’s approach is a projection of emissions based only on the assumption that in developing countries, per capita emissions will increase as a function of growth in per capita income. Her approach yields an estimated projection of a twenty-fold increase in fossil fuel emissions. None of the three projections takes into account the possibility of policy changes that would alter patterns in fuel emissions.
For the year 2050, the differences in projected total emissions from developing nations are between 1.3 billion and 5 billion metric tons. Although the differences are large, they represent only 15% (in the EPA model) and 9% (in the author’s model) of total emissions in developing countries. This data implies that even with lower population growth, emissions would have increased by almost six times their starting level. Birdsall gives three main reasons why policies to reduce population growth in developing countries would not contribute much in the way of reducing fossil fuel emissions. Her first explanation is that in most countries, even if the fertility rate were to suddenly decrease to the replacement rate, demographic momentum would still mean that populations doubled in size. This momentum is due to the high fertility and low mortality associated with the past few decades. Birdsall explains that even if the number of births per women were to decline, the number of women having children will be increasing more rapidly. She claims that even by using the rapid fertility decline model, if developed nations lowered their emissions rates to the current world average and developing nations had similar rates, total global emissions would still double. Secondly, developing countries have the most potential for affecting the size of the future population and they also have low per capita emissions. Population reduction in these countries is therefore less correlated to a reduction in emissions. Thirdly, smaller populations will substitute energy for labor in production, causing higher per capita emissions. As a consequence of this, rapid fertility decline may further exaggerate that difference.
The effect of slower population growth on deforestation is, Birdsall shows, also less significant than one might think. Although deforestation and population growth are correlated, other factors need to be mentioned. The major causes of deforestation are the clearing of forests for agricultural land and the use of wood for fuel; both of which increase as growing populations increase the pressure on the land and energy resources available to them. Analyses of these relationships project that a 50% difference in the rate of population growth would reduce the deforestation rate by 25%. However, it is estimated that 90% of increases in agricultural production do not involve clearing forest land for farming; rather, the increases are due to higher yields on existing production sites. Similarly, the use of wood as fuel declines as household income and city sizes increase, implying that the pressure on forests will be reduced as income growth and urban areas expand. The reductions predicted are also only projected until the year 2025. Beyond 2025, a decline in population growth will have less of an effect on deforestation because the forest base will be lower and because the difference in population projections drops off quickly after this. What all of these projections mean is that a decline in population growth will yield at best a short-term decline in deforestation rates.
Since Birdsall has shown that decreasing the rate of population growth will not significantly change the rate of emissions in the long-term, she studies what the costs of programs to reduce fertility rates would be and whether or not their value in terms of emissions reductions is worthwhile. The three methods she explores are a carbon tax, family planning, and the education of girls. The carbon tax is derived from behavioral models of supply and demand where assumptions are made about technological change, fuel substitution, and the elasticity of the energy supply. By finding the marginal cost of reducing emissions, it is possible to determine the required tax for the reduction. The cost reduction shows that the marginal cost of reducing carbon emissions by 10% would be about $20 per ton, while a 20% reduction would require a tax of over $50 per ton. The costs of further reductions are projected to rise rapidly.
In the family planning model, Birdsall explores a study by Cochrane and Sai (1991), which calculated the costs of contraceptives in a year for different countries. They then translated these costs into the costs of averted births. The results showed three different costs per birth averted for three different kinds of countries; in high-mortality countries where 20% of women reported not wanting more children, the cost was $259 per birth; in high–mortality countries where 30% of women did not want more children, the cost was $213; and in low-mortality countries where 45% of women did not want more children, the cost was $144. When combined with data concerning the cost of reducing emissions, the study found that family planning meant spending between $4 and $11 per ton to reduce carbon emissions. They noted that in countries such as Thailand, where family planning services are already well in place, marginal costs could increase unless improvements in contraceptive technology drive down those costs. The average of $220 per birth averted for the three different kinds of countries means that more than 27million births could be averted per year and that potentially emissions could be reduced by anywhere between 540 million and 1.6 billion tons if $6 billion dollars were spent on family planning programs. A $6 billion expenditure with the carbon tax was less cost effective, as it only reduced emissions by 10%. The main challenge in family planning programs is that while costs are immediate, the results and benefits from the spending take longer to take effect.
Birdsall’s final cost analysis is of adding one additional year of schooling to girls’ education in developing countries. In a study by Summers (1992), it was shown that one additional year of schooling reduces fertility by about 10%. Summers also estimates that in order to raise female enrollment to the level of developed nations, the program would cost about $6 billion. One year of primary schooling, according to World Bank reports, averages about $36 per student in developing countries. With $6 billion, 112 million more years of school could be gained and eventually there would be an annual reduction of births of about 34 million. From Birdsall’s findings, it seems that the most cost effective ways to reduce population growth and reduce emissions are through female schooling initiatives and family planning, as the carbon tax did much less to reduce emissions with a $6 billion investment.
Birdsall has shown that, although a decline in population growth does not always mean a reduction in emissions and a solution to the problem of global warming, there are in fact ways for countries to invest in programs such as family planning and female education efforts that will address emissions reductions in conjunction with reducing the rate of fertility. If the resources are available to support these efforts, feasible reductions in population growth will help reduce the carbon emissions that cause global warming and will yield positive results.
Honor Code:
I have neither given nor received aid on this paper.
Sarah Day
References:
Nancy Birdsall. "Another Look at Population and Global Warming" Population and Development, United Nations, New York, 1994.