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The Impact of Population Growth on Global Warming

By Ali Connolly

The burning of stored carbon and other fossil fuels, along with deforestation has led to increased carbon dioxide levels, which are creating drastic effects on the entire global climate. This global warming is an issue of concern for people of all nations because the effects are not localized, but rather global. Environmentalists, economists and politicians have become increasingly concerned with the potential effects of this climate change and the possible solutions. Although there is a great deal of debate on the issue, certain facts have been agreed upon. Human activity, most significantly the burning of fossil fuel, has resulted in extreme increases in the concentrations of greenhouse gases in our atmosphere. As these emissions continue to grow we can expect increases in the global temperature. Less concrete knowledge has been found about the future consequences of this global warming; however, some obvious results will be a rise in sea level, changes in weather patterns, and more temperate land conditions.

This paper will examine to what extend population growth is facilitating global warming. The investigation of three separate articles pertaining to the subject will provide a better understanding of the factors which effect global warming, along with the role of developed and less developed countries, and the importance of proper measurement and model specification.

When addressing a pertinent issue, such as global warming, accurate data and precise projections for the future are crucial. In "World Population, Economic Growth, and Energy Demand, 1990-2100: A Review of Projections", Bernard Gilland assesses the World Energy Council’s (WEC) projections for world population, energy consumption and several other factors. For all projections the WEC produced a high, medium and low estimate. In projecting population size the WEC assumed that the world fertility rate would be at the replacement level before the turn of the 21st century. The medium projection for population size in 2100 is about 12 billion people. The WEC is quick to remind readers that "population forecasting has long been a hazardous business" (Gilland 512).

The projections for economic growth are based on the assumption that economic growth will continue to exceed population growth rates throughout the 21st century. The WEC predicts that the growth rate of GDP will be 2.4% in the developed countries and 4.6% in the less developed countries.

Energy intensity is a measure of energy consumption per unit of GDP. This is a complicated measure for the WEC to predict because it involves estimates of two variables that are both highly variant themselves. The important issue is that all projections show increases in the energy consumption as we approach 2020. The WEC also explores the option of shifting from fossil fuel consumption to alternative energy sources such as nuclear, hydroelectricity and solar energy. Although the WEC’s projections may be scrutinized for their enormous uncertainty, there is no dispute that CO2 concentration in the atmosphere has increased at a high rate and will inevitability have consequences for our global environment. In order to slow this global warming it is essential to determine the factors which affect CO2 emission.

John Bongaarts investigates the effects of population on global climate change in his article entitled "Population Growth and Global Warming". Human activities, such as the burning of fossil fuels and deforestation, have led to an upsurge in the emission of greenhouse gases which have changed the structure of our climate resulting in global warming.

Bongaarts proposed that it is necessary to look at the conditions of global warming "in the absence of intervention" to serve as a benchmark for policies to reduce climate change (Bongaarts 301). Without intervention, CO2 emission rates are predicted to double by 2025, an increase four-fold by 2100. Predictions show that this would result in a temperature increase of 4 degrees Celsius by the year 2100.

Bongaarts then formulated a model that determined the factors that affect the emission of CO2 into the atmosphere. His findings show that five variables affect CO2 production; they are population size, gross domestic product per capita, energy intensity of GDP, tropical deforestation and carbon intensity of energy consumption. The energy intensity is a measure of the efficiency of energy use and varies drastically across countries. For example, the energy intensity in the former Soviet Union is much higher than it is in the United States because our industry is much more efficient. The carbon intensity is a measure of the percentage of energy production resulting from the burning of fossil fuel. Countries that put more of an emphasis on alternative energy sources, such as hydroelectric power, will have much lower carbon intensity measures than those countries which rely entirely on the burning of coal for energy.

After determining that CO2 emission is primarily affected by the aforementioned variables, it is important to view the projections for these factors to determine what CO2 emission will be in our future. Population size is expected to increase, but at varying rates across the world. Researchers predict 9 billion people will be living in more developed countries and 1.5 billion in the less developed countries by the year 2100.

The second variable, GDP per capita, is expected to reach $36,000 by 2100, as opposed to $3,000 in 1985. Growth rates of GDP per capita are predicted to increase at a decreasing rate. On the other hand, energy intensity is expected to rapidly decline. As less developed countries become more efficient in energy use this will spark the decline in energy intensity. Carbon intensity is predicted to remain unchanged. Developed countries will use less fossil burning energy sources, but this will be offset by the industrialization of developed countries. In the future a slow rise in deforestation is expected. Using all of these projections of the variables that influence CO2 emission Bongaarts was able to make predictions about the level of emissions in the year 2100. These finding show a 4.4 degree Celsius temperature rise, with CO2 concentrations reaching 940 parts per million in 2100 as opposed to 346 ppm in 1985.

Perhaps the most interesting conclusion is that "further population growth and economic development are expected to be the principal factors putting upward pressure on annual CO2 emission rates" (Bongaarts 307). The model predicts that population growth will be responsible for 35% of the increase in emissions.

Bongaarts goes on to address possible policy implications to slow the climate change problem. These findings suggest that efforts to decrease population growth will aid in the reduction of future concentration of greenhouse gases in the atmosphere. A second policy approach would involve emission controls, which would attempt to stabilize the level of CO₂ in the environment. Unfortunately, even if stabilization were reached today global warming would continue for several decades. This phenomenon is called "unrealized warming". The effectiveness of a policy of this type would hinge on the three following factors: the determined level, the timing of reaching this level, and the degree of participation of countries. Obviously, the sooner stabilization policies are implemented the more effective they will be in controlling global warming. However, participation rates will play a large role in the effectiveness of any stabilization policy. The developed countries are currently responsible for eighty percent of global warming, yet projections show that the growth rate of CO2 emission is expected to be much higher in the less developed countries. Countries will have an incentive to ‘free-ride’: avoid action to slow global warming, because they will experience the benefits of other countries pursuing such action. Since less developed countries have large growing populations they will play an increasing role in the production rates of greenhouse gases in the future. Despite this knowledge, it is improbable to assume that less developed countries are willing to allocate funds for the improvement of environmental issues, when so many other problems persist. Control efforts which target only developed countries will become less efficient over time as developing countries increasingly contribute to global warming.

Bonbaards proposes a last policy solution of reducing the carbon intensity of energy production. This would involve shifts from fossil fuel burning energy sources to alternative sources of energy. These alternative sources include hydroelectric power, solar energy, and other nonfossil fuel energy sources.

Bonbaards suggests that the most effective solution for slowing global warming is to change all of the determinants which increase the emission of CO2 gases. Many of these policies, including control measures, are costly and may interfere with economic growth. Although many factors play a role, population growth "is a key determinant of greenhouse gas emission, and efforts to slow population growth in both the developed and developing world should be an essential element of a comprehensive policy to reduce global warming" (Bonbaards 316).

Similar to Bonbaards, MacKellar, Lutz, Prinz, and Goujon address the factors which influence environmental impacts in their article entitled, "Population, Households, and CO2 Emissions". They focus their attention on the choice of the demographic unit, and question whether it is accurate to use the individual as the consuming unit. Instead, they propose that the household should be used as the demographic unit. This is an important issue because this change would shift the focus from the rate of growth and size of the population to the rate of growth and the number of households. MacKellar et al illustrate that this change results in very different conclusions.

Their argument is that economies of scale exist in energy consumption. Many decisions about energy consumption are made at the household level as opposed to the individual level. For instance, automobile and electricity use decisions depend more on the household than the individual. For example, a doubling of family members will not result in a doubling of the amount of electricity used. Data demonstrate that from 1950 to 1990 family household size declined in the more developed regions due to changes in the age structure of the population. Along with these changes came an increase in the number of households, because children left the home earlier and the growing trend of the elderly to live on their own. This reduction in extended family is a result of ‘modernization’. As the standard of living increases average household size declines. This is due in part to changes in attitudes regarding family formation and the ability of each individual to attain separate living arrangements.

This data led MacKellar et al to call for a change in the presently excepted model used for distinguishing the relationship between global environmental impacts and population growth. The current model, referred to as the I=PAT, lists population (P), affluence measured by GDP per capita (A), and technological efficiency (T) as the determinants of the level of environmental impact (I). Their suggestion calls for a shift to an I=HAT model where H stands for households and affluence is measured as GDP per household. This small change has large implications for interpretation of data. When applied to an example of energy consumption they found that using the I=HAT identity about seventy-five percent of the rate of growth was due to growth in the number of families, as opposed to one-third accounted for by the I=PAT identity. Thus, the conclusion follows that a shift to a more ‘modernized’ family formation has been a large factor in the rise in energy consumption.

These findings raise an important issue about the effects of population growth on environmental factors, such as global warming. At first declines in fertility rates will result in a reduction in population growth which will alleviate some of the pressure placed on the environment. As the age structure changes and the population becomes older, more households will be formed increasing the pressure on the environment. This means that the effect of declining fertility on environmental problems is somewhat unclear.

As we continue into the 21st century we will continue to see age-structure changes in population which will result in a higher percentage of people over the age of sixty. This means "the number of households will grow more rapidly than the number of people" (MacKellar et al, 862). In their research, MacKellar et al direct their attention to the importance of the unit of demographic measure. They looked at the difference between using individuals versus households, however they did not conclude that this is necessarily the correct measure. Maybe the community is in fact an appropriate starting point. Regardless, they point to the importance of identifying the demographic unit before making decisive conclusions about the effects of population on the environment.

Global warming is an environmental issue which affects everyone on the planet. It will continue to affect our climate for many decades even if reductions to sustainable levels of greenhouse gas emission were achieved today. Global warming has triggered a policy debate that has caused researchers to further investigate the factors contributing to its growth. One such factor is population growth. From the research presented in the three aforementioned articles it appears that although population growth may lead to further environmental impacts, it is not the solitary component. The high uncertainty of forecasting, coupled with the debate over current models which include the individual as the unit of consumption make it difficult to reach conclusive results. Although slowing of population growth will most likely facilitate the slowing of global warming it is by no means the end all; we must conduct "further research before attempting to draw firm conclusions or take drastic action" (Bongaarts 299).

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